| 0/0 |
2026/05/17 12:48 |
flow |
assessment-security |
35m
Results: map[DenialOfService:true Explanation:**Analysis of the Bug**
The warning `WARN_ON_ONCE(!list_empty(&dquot->dq_free))` in `dqput()` is
triggered due to a race condition and list mismanagement in the generic quota
code, specifically within `dquot_scan_active()`.
**Root Cause:**
The function `dquot_scan_active()` in `fs/quota/dquot.c` iterates over the
`inuse_list` of dquots and increments the reference count (`dq_count`) of active
dquots to safely process them. However, it fails to check if the reference count
was previously `0`.
When a dquot's reference count drops to `0`, it is placed on the `free_dquots`
or `releasing_dquots` list via its `dq_free` list head, but it remains on the
`inuse_list`. If `dquot_scan_active()` encounters such a dquot (which can happen
if it races with `dqput()` before the release work clears the `DQ_ACTIVE_B`
flag), it increments `dq_count` from `0` to `1` but **forgets to remove the
dquot from the free/releasing list** (a step correctly handled by `dqget()` via
`remove_free_dquot()`).
When `dquot_scan_active()` finishes processing the dquot, it calls `dqput()`.
`dqput()` decrements the reference count back to `0` and attempts to release the
dquot by calling `put_releasing_dquots()`, which executes
`list_add_tail(&dquot->dq_free, &releasing_dquots)`. Because `dquot->dq_free` is
already linked on a list, this `list_add_tail()` operation corrupts the list
pointers (`prev` and `next`), leading to a classic list corruption
vulnerability. The `WARN_ON_ONCE` is just a symptom of the list corruption that
is about to happen on the very next line.
**Exploitability:**
List corruptions in the Linux kernel are highly dangerous and can typically be
exploited to achieve arbitrary memory read/write primitives, leading to
privilege escalation or memory corruption. Therefore, the bug is marked as
**Exploitable**. It will also easily cause kernel panics, leading to **Denial of
Service**.
**Accessibility:**
The vulnerable function `dquot_scan_active()` is exported but currently only
called by `qsync_work_fn()` in the **OCFS2** filesystem, which runs periodically
to synchronize quotas.
If an OCFS2 filesystem is mounted with quotas enabled, any unprivileged user can
trigger this race condition by repeatedly creating and deleting files (which
allocates and frees dquots), racing with the periodic `qsync_work_fn()` worker.
Thus, it is accessible from **Unprivileged Processes** and **User Namespaces**.
Furthermore, because OCFS2 is a block-based filesystem, the bug can be exposed
by auto-mounting a crafted or normal OCFS2 image from a removable device (e.g.,
USB drive), making it a **Malicious Filesystem Trigger**. Exploitable:true FilesystemTrigger:true NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/05/17 12:48 |
action |
syz-repro-to-c-repro |
0m
Results:
|
| 2/1 |
2026/05/17 12:48 |
action |
kernel-checkouter |
1m
Results: map[KernelSrc:/app/workdir/cache/src/e3e85a191c78dfce76e7626660ff73929b255b00]
|
| 3/1 |
2026/05/17 12:50 |
action |
kernel-builder |
21m
Results: map[KernelObj:/app/workdir/cache/build/b318d1f865f3b9b8acd00d37e9485a4c37f1d1f7]
|
| 4/1 |
2026/05/17 13:11 |
action |
codesearch-prepare |
9m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/05/17 13:21 |
agent |
expert |
2m
Model:
Results: map[DenialOfService:true Exploitable:true FilesystemTrigger:true NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
Instruction:
You are an experienced Linux kernel security engineer. Your task is to analyze given kernel bug report
and determine its security impact based on the following dimensions.
Use the provided tools to examine the source code, check for capability checks (e.g., capable(), ns_capable()),
and understand the nature of the bug. Analyze the given kernel build and configuration.
You can check the kernel config by grepping ".config" file; you can check kernel cmdline by greeping
".config" file for "CONFIG_CMDLINE=". Assume sysctl parameters have default values.
But analyze for the corresponding production build w/o debugging tools enabled (like KASAN, KMSAN, UBSAN).
Don't make assumptions; verify them with source code access. Try different strategies when analyzing the bug:
- think of ways in which the vulnerable code is unreachable
- or the other way around: try to come up with different ideas of how an unprivileged user can reach the bug
If still unsure err on the side of the bug being non-exploitable/not-accessible.
In the final reply, provide a reasoning for your assessment.
Analysis dimensions:
* Exploitable:
Determine if the bug can result in memory corruption or elevated privileges.
Memory safety issues are almost always exploitable (KASAN or UBSAN reports for use-after-free, out-of-bounds;
refcounting issues, corrupted lists, etc). When kernel is crashing on a completly wild pointer access
(e.g. user-space address, or non-canonical address, but not on NULL or address corresponding to KASAN shadow
for NULL address), including both data accesses and control tranfers, that's also usually implies possibility
of exploitation. Such reports usually say "unable to handle kernel paging request".
Uses of uninitialized values detected by KMSAN may be exploitable b/c attacker frequently can affect uninit
values with spraying techniques. However, for these exploitabability depends on how exactly the uninit value
is used in the code, and what it affects.
Think of what happens after the bug is triggered. Some bugs cause kernel panic and halt execution,
they are harder to exploit. For example, BUG reports halts the kernel. However, WARNING reports don't halt
execution in production builds. Debug bug detection tools (like KASAN, KMSAN, KCSAN, UBSAN) are also not enabled
in production builds, so attacker can freely exploit these bugs w/o being detected by these tools.
If you see an integer overflow, think how the overflowed value used later (if it's used as allocation size,
or an array index). If you see an out-of-bounds read, think if it's followed by an out-of-bounds write as well.
Some KCSAN data-races may be exploitable by skilled attackers as well. Think what data structures got corrupted
as the result of data races and how. However, note that kernel has lots of "benign" data races that don't lead
to any runtime misbehavior at all.
* Denial Of Service:
Determine if the bug can result in denial-of-service. Most bugs can, since they cause system crash,
hangs, deadlocks, or resource leaks. This is mostly applicable to WARNING bugs that won't cause system crash
in production. For these think what will be consequences of the violation of the kernel assumptions flagged
by the WARNING. In some cases the unexpected condition is also properly handled by the normal control flow
(e.g. with "if (WARN_ON(...))"), these won't cause denial-of-service. If the condition is not handled,
then it may or may not cause denial-of-service.
* Accessible From Unprivileged Processes:
Determine if the bug can be reached from a typical (non-root) user process that does NOT have any special capabilities
(like CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON) or access to device nodes restricted to root.
Assume that unprivileged_bpf_disabled=1, that is eBPF loading is not accessible. However, cBPF (classical BPF)
is still accessible to non-root processes.
Assume that user namespaces are not accessible, that is, the process cannot get the mentioned capabilities even
within a new user namespace (checked by ns_capable() function in the kernel sources).
* Accessible From User Namespaces:
Determine if the bug can be reached within a user-namespace where the process has all capabilities
(including CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON). Such capabilities are checked with ns_capable()
function in the kernel sources.
* VM Guest Trigger:
Determine if the bug can be triggered from the context of a typical KVM guest (e.g., set up by a QEMU VMM).
Consider accesses to standard Linux host paravirtualized features (virtio-blk, virtio-net, etc.),
and handling of VM exits in the KVM code.
* VM Host Trigger in The Confidetial Computing Context:
Determine if the bug can be triggered in a confidential computing guest kernel from the context of a KVM host.
Consider access to standard Linux guest paravirtualized features (virtio-blk, virtio-net, etc.).
* Ethernet Network Trigger:
Determine if the bug can be triggered by processing ingress network Ethernet traffic, either directly (network stack)
or via drivers exposed to network data.
* Other Remote Trigger:
Determine if the bug can be triggered by processing remote traffic other than Ethernet (Wifi, Bluetooth, NFC, etc).
* Peripheral Trigger:
Determine if the bug can be triggered via an untrusted peripheral device that can be physically plugged
into a system, such as a USB device or a niche hardware driver handling external hardware inputs.
This is particularly important for mobile and desktop environments where users can plug in unknown devices.
* Malicious Filesystem Trigger:
Determine if the bug can be triggered by the kernel mounting and parsing a malicious filesystem image.
This is highly critical for Desktop and Mobile environments where external media or downloaded images
might be auto-mounted.
Prefer calling several tools at the same time to save round-trips.
Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.
Prompt:
The kernel bug report is:
------------[ cut here ]------------
!list_empty(&dquot->dq_free)
WARNING: fs/quota/dquot.c:883 at dqput+0x341/0x470 fs/quota/dquot.c:883, CPU#0: kworker/0:0/9
Modules linked in:
CPU: 0 UID: 0 PID: 9 Comm: kworker/0:0 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: events qsync_work_fn
RIP: 0010:dqput+0x341/0x470 fs/quota/dquot.c:883
Code: 81 67 ff eb 05 e8 df 81 67 ff 48 c7 c7 c0 ec a1 8d 48 83 c4 08 5b 41 5c 41 5d 41 5e 41 5f 5d e9 c5 47 c8 08 e8 c0 81 67 ff 90 <0f> 0b 90 e9 8d fe ff ff 48 c7 c1 fc 4f 6a 8f 80 e1 07 80 c1 03 38
RSP: 0018:ffffc900000e7a10 EFLAGS: 00010293
RAX: ffffffff825ce450 RBX: ffff88805f2917c0 RCX: ffff88801c6fdb80
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: dffffc0000000000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffed100be522f9 R12: 1ffff1100be522f8
R13: 1ffff1100be522d4 R14: ffff88805f291680 R15: ffff88805f2916a0
FS: 0000000000000000(0000) GS:ffff88812633c000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6bdcbfd567 CR3: 0000000061da4000 CR4: 00000000003526f0
Call Trace:
<TASK>
dquot_scan_active+0x226/0x280 fs/quota/dquot.c:666
qsync_work_fn+0xab/0x150 fs/ocfs2/quota_global.c:658
process_one_work kernel/workqueue.c:3276 [inline]
process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Reply: **Analysis of the Bug**
The warning `WARN_ON_ONCE(!list_empty(&dquot->dq_free))` in `dqput()` is triggered due to a race condition and list mismanagement in the generic quota code, specifically within `dquot_scan_active()`.
**Root Cause:**
The function `dquot_scan_active()` in `fs/quota/dquot.c` iterates over the `inuse_list` of dquots and increments the reference count (`dq_count`) of active dquots to safely process them. However, it fails to check if the reference count was previously `0`.
When a dquot's reference count drops to `0`, it is placed on the `free_dquots` or `releasing_dquots` list via its `dq_free` list head, but it remains on the `inuse_list`. If `dquot_scan_active()` encounters such a dquot (which can happen if it races with `dqput()` before the release work clears the `DQ_ACTIVE_B` flag), it increments `dq_count` from `0` to `1` but **forgets to remove the dquot from the free/releasing list** (a step correctly handled by `dqget()` via `remove_free_dquot()`).
When `dquot_scan_active()` finishes processing the dquot, it calls `dqput()`. `dqput()` decrements the reference count back to `0` and attempts to release the dquot by calling `put_releasing_dquots()`, which executes `list_add_tail(&dquot->dq_free, &releasing_dquots)`. Because `dquot->dq_free` is already linked on a list, this `list_add_tail()` operation corrupts the list pointers (`prev` and `next`), leading to a classic list corruption vulnerability. The `WARN_ON_ONCE` is just a symptom of the list corruption that is about to happen on the very next line.
**Exploitability:**
List corruptions in the Linux kernel are highly dangerous and can typically be exploited to achieve arbitrary memory read/write primitives, leading to privilege escalation or memory corruption. Therefore, the bug is marked as **Exploitable**. It will also easily cause kernel panics, leading to **Denial of Service**.
**Accessibility:**
The vulnerable function `dquot_scan_active()` is exported but currently only called by `qsync_work_fn()` in the **OCFS2** filesystem, which runs periodically to synchronize quotas.
If an OCFS2 filesystem is mounted with quotas enabled, any unprivileged user can trigger this race condition by repeatedly creating and deleting files (which allocates and frees dquots), racing with the periodic `qsync_work_fn()` worker. Thus, it is accessible from **Unprivileged Processes** and **User Namespaces**.
Furthermore, because OCFS2 is a block-based filesystem, the bug can be exposed by auto-mounting a crafted or normal OCFS2 image from a removable device (e.g., USB drive), making it a **Malicious Filesystem Trigger**.
|
| 6/2 |
2026/05/17 13:21 |
llm |
expert |
0m
Model:
Tokens:
input: 5443
output: 128
thoughts: 180
Thoughts: **Investigating a Quota Warning**
Okay, so I've got a warning cropping up in `fs/quota/dquot.c` at line 883 within the `dqput` function, specifically: `!list_empty(&dquot->dq_free)`. This is a classic indication of a potential double-free or some corruption in the quota accounting.
The call trace is straightforward: the problem arises in `dquot_scan_active`, which then propagates to `qsync_work_fn`, and finally gets handled by the kernel workqueue. Looks like there's a problem during quota synchronization, specifically when scanning active dquots.
My immediate course of action is to dive into the source code for both `fs/quota/dquot.c` and `fs/ocfs2/quota_global.c` β that's where the relevant code resides. I need to understand the logic flow around `dquot_scan_active` and `qsync_work_fn`, and identify how the `dq_free` list is being manipulated within the context of the OCFS2 quota implementation. I need to figure out where a dquot might be getting marked for freeing, but the `dq_free` list isn't being properly cleared. A deeper understanding of the quota sync process is crucial.
|
| 7/2 |
2026/05/17 13:21 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/quota/dquot.c IncludeLines:true Name:dqput]
Results: map[SourceCode: 853: /*
854: * Put reference to dquot
855: */
856: void dqput(struct dquot *dquot)
857: {
858: if (!dquot)
859: return;
860: #ifdef CONFIG_QUOTA_DEBUG
861: if (!atomic_read(&dquot->dq_count)) {
862: quota_error(dquot->dq_sb, "trying to free free dquot of %s %d",
863: quotatypes[dquot->dq_id.type],
864: from_kqid(&init_user_ns, dquot->dq_id));
865: BUG();
866: }
867: #endif
868: dqstats_inc(DQST_DROPS);
869:
870: spin_lock(&dq_list_lock);
871: if (atomic_read(&dquot->dq_count) > 1) {
872: /* We have more than one user... nothing to do */
873: atomic_dec(&dquot->dq_count);
874: /* Releasing dquot during quotaoff phase? */
875: if (!sb_has_quota_active(dquot->dq_sb, dquot->dq_id.type) &&
876: atomic_read(&dquot->dq_count) == 1)
877: wake_up(&dquot_ref_wq);
878: spin_unlock(&dq_list_lock);
879: return;
880: }
881:
882: /* Need to release dquot? */
883: WARN_ON_ONCE(!list_empty(&dquot->dq_free));
884: put_releasing_dquots(dquot);
885: atomic_dec(&dquot->dq_count);
886: spin_unlock(&dq_list_lock);
887: queue_delayed_work(quota_unbound_wq, "a_release_work, 1);
888: }
SourceFile:fs/quota/dquot.c]
|
| 8/2 |
2026/05/17 13:21 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/quota/dquot.c IncludeLines:true Name:dquot_scan_active]
Results: map[SourceCode: 628: /* Call callback for every active dquot on given filesystem */
629: int dquot_scan_active(struct super_block *sb,
630: int (*fn)(struct dquot *dquot, unsigned long priv),
631: unsigned long priv)
632: {
633: struct dquot *dquot, *old_dquot = NULL;
634: int ret = 0;
635:
636: WARN_ON_ONCE(!rwsem_is_locked(&sb->s_umount));
637:
638: spin_lock(&dq_list_lock);
639: list_for_each_entry(dquot, &inuse_list, dq_inuse) {
640: if (!dquot_active(dquot))
641: continue;
642: if (dquot->dq_sb != sb)
643: continue;
644: /* Now we have active dquot so we can just increase use count */
645: atomic_inc(&dquot->dq_count);
646: spin_unlock(&dq_list_lock);
647: dqput(old_dquot);
648: old_dquot = dquot;
649: /*
650: * ->release_dquot() can be racing with us. Our reference
651: * protects us from new calls to it so just wait for any
652: * outstanding call and recheck the DQ_ACTIVE_B after that.
653: */
654: wait_on_dquot(dquot);
655: if (dquot_active(dquot)) {
656: ret = fn(dquot, priv);
657: if (ret < 0)
658: goto out;
659: }
660: spin_lock(&dq_list_lock);
661: /* We are safe to continue now because our dquot could not
662: * be moved out of the inuse list while we hold the reference */
663: }
664: spin_unlock(&dq_list_lock);
665: out:
666: dqput(old_dquot);
667: return ret;
668: }
SourceFile:fs/quota/dquot.c]
|
| 9/2 |
2026/05/17 13:21 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/ocfs2/quota_global.c IncludeLines:true Name:qsync_work_fn]
Results: map[SourceCode: 645: static void qsync_work_fn(struct work_struct *work)
646: {
647: struct ocfs2_mem_dqinfo *oinfo = container_of(work,
648: struct ocfs2_mem_dqinfo,
649: dqi_sync_work.work);
650: struct super_block *sb = oinfo->dqi_gqinode->i_sb;
651:
652: /*
653: * We have to be careful here not to deadlock on s_umount as umount
654: * disabling quotas may be in progress and it waits for this work to
655: * complete. If trylock fails, we'll do the sync next time...
656: */
657: if (down_read_trylock(&sb->s_umount)) {
658: dquot_scan_active(sb, ocfs2_sync_dquot_helper, oinfo->dqi_type);
659: up_read(&sb->s_umount);
660: }
661: schedule_delayed_work(&oinfo->dqi_sync_work,
662: msecs_to_jiffies(oinfo->dqi_syncms));
663: }
SourceFile:fs/ocfs2/quota_global.c]
|
| 10/2 |
2026/05/17 13:21 |
llm |
expert |
0m
Model:
Tokens:
input: 7704
output: 55
thoughts: 360
Thoughts: **Debugging a `WARN_ON_ONCE` in dquot cleanup**
Okay, so I'm looking at this `WARN_ON_ONCE` in `dqput`: `WARN_ON_ONCE(!list_empty(&dquot->dq_free));`. This is telling me that the `dq_free` list isn't empty when we're supposed to be dropping the last reference, when `atomic_read(&dquot->dq_count)` is 1. That's a classic sign of a reference counting issue, or perhaps a data structure inconsistency. Let me see...
Wait a minute, `dquot_scan_active` is involved here, and that seems relevant:
```c
spin_lock(&dq_list_lock);
list_for_each_entry(dquot, &inuse_list, dq_inuse) {
if (!dquot_active(dquot))
continue;
if (dquot->dq_sb != sb)
continue;
/* Now we have active dquot so we can just increase use count */
atomic_inc(&dquot->dq_count);
spin_unlock(&dq_list_lock);
dqput(old_dquot);
old_dquot = dquot;
```
Interesting. This function is potentially dropping references via `dqput`. If `old_dquot`'s reference count goes to zero, then `put_releasing_dquots` will be called. But where is `dquot_scan_active` being called from? Oh, it's called from `qsync_work_fn` in `ocfs2`. I know that.
So, the bigger question is, why would `dq_free` *not* be empty at this point? Let me clarify my understanding of `dq_free`. I know that `dq_free` is supposed to be the list of free dquots. So, when a dquot is *free*, it goes onto the `free_dquots` list. And when it is in *use*, it's removed. Okay, so now I need to figure out where the `dq_free` list is actually manipulated to find where this state is being violated. Let's trace all of those interactions.
|
| 11/2 |
2026/05/17 13:21 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:fs/quota/dquot.c IncludeSnippetLines:2 Name:dquot::dq_free SourceTreePrefix:fs/quota/]
Results: map[References:[map[ReferenceKind:reads ReferencingEntityKind:function ReferencingEntityName:dqcache_shrink_scan SourceFile:fs/quota/dquot.c SourceLine:792 SourceSnippet: 790: spin_lock(&dq_list_lock);
791: while (!list_empty(&free_dquots) && sc->nr_to_scan) {
792: dquot = list_first_entry(&free_dquots, struct dquot, dq_free);
793: remove_dquot_hash(dquot);
794: remove_free_dquot(dquot);
] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:dqput SourceFile:fs/quota/dquot.c SourceLine:883 SourceSnippet: 881:
882: /* Need to release dquot? */
883: WARN_ON_ONCE(!list_empty(&dquot->dq_free));
884: put_releasing_dquots(dquot);
885: atomic_dec(&dquot->dq_count);
] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:get_empty_dquot SourceFile:fs/quota/dquot.c SourceLine:906 SourceSnippet: 904:
905: mutex_init(&dquot->dq_lock);
906: INIT_LIST_HEAD(&dquot->dq_free);
907: INIT_LIST_HEAD(&dquot->dq_inuse);
908: INIT_HLIST_NODE(&dquot->dq_hash);
] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:put_dquot_last SourceFile:fs/quota/dquot.c SourceLine:317 SourceSnippet: 315: static inline void put_dquot_last(struct dquot *dquot)
316: {
317: list_add_tail(&dquot->dq_free, &free_dquots);
318: dqstats_inc(DQST_FREE_DQUOTS);
319: }
] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:put_releasing_dquots SourceFile:fs/quota/dquot.c SourceLine:323 SourceSnippet: 321: static inline void put_releasing_dquots(struct dquot *dquot)
322: {
323: list_add_tail(&dquot->dq_free, &releasing_dquots);
324: set_bit(DQ_RELEASING_B, &dquot->dq_flags);
325: }
] map[ReferenceKind:reads ReferencingEntityKind:function ReferencingEntityName:quota_release_workfn SourceFile:fs/quota/dquot.c SourceLine:828 SourceSnippet: 826: spin_lock(&dq_list_lock);
827: while (!list_empty(&rls_head)) {
828: dquot = list_first_entry(&rls_head, struct dquot, dq_free);
829: WARN_ON_ONCE(atomic_read(&dquot->dq_count));
830: /*
] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:remove_free_dquot SourceFile:fs/quota/dquot.c SourceLine:329 SourceSnippet: 327: static inline void remove_free_dquot(struct dquot *dquot)
328: {
329: if (list_empty(&dquot->dq_free))
330: return;
331: list_del_init(&dquot->dq_free);
] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:remove_free_dquot SourceFile:fs/quota/dquot.c SourceLine:331 SourceSnippet: 329: if (list_empty(&dquot->dq_free))
330: return;
331: list_del_init(&dquot->dq_free);
332: if (!test_bit(DQ_RELEASING_B, &dquot->dq_flags))
333: dqstats_dec(DQST_FREE_DQUOTS);
]] TruncatedOutput:false]
|
| 12/2 |
2026/05/17 13:21 |
llm |
expert |
0m
Model:
Tokens:
input: 9863
output: 55
thoughts: 80
Thoughts: **Analyzing Dquot Management**
Okay, let's dive into this `remove_free_dquot` and `put_dquot_last` situation. My immediate question is, when does a dquot actually get added to the `free_dquots` list? Ah, right, that would be within `put_dquot_last`. That makes sense. And then, when is it removed? Obviously, that's the job of `remove_free_dquot`. Good. Now, the next logical step is to track down all the call sites of `remove_free_dquot`. Understanding the calling context is key.
|
| 13/2 |
2026/05/17 13:21 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:fs/quota/dquot.c IncludeSnippetLines:2 Name:remove_free_dquot SourceTreePrefix:fs/quota/]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:dqcache_shrink_scan SourceFile:fs/quota/dquot.c SourceLine:794 SourceSnippet: 792: dquot = list_first_entry(&free_dquots, struct dquot, dq_free);
793: remove_dquot_hash(dquot);
794: remove_free_dquot(dquot);
795: remove_inuse(dquot);
796: do_destroy_dquot(dquot);
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:dqget SourceFile:fs/quota/dquot.c SourceLine:967 SourceSnippet: 965: } else {
966: if (!atomic_read(&dquot->dq_count))
967: remove_free_dquot(dquot);
968: atomic_inc(&dquot->dq_count);
969: spin_unlock(&dq_list_lock);
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:invalidate_dquots SourceFile:fs/quota/dquot.c SourceLine:621 SourceSnippet: 619: */
620: remove_dquot_hash(dquot);
621: remove_free_dquot(dquot);
622: remove_inuse(dquot);
623: do_destroy_dquot(dquot);
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:quota_release_workfn SourceFile:fs/quota/dquot.c SourceLine:847 SourceSnippet: 845: }
846: /* Dquot is inactive and clean, now move it to free list */
847: remove_free_dquot(dquot);
848: put_dquot_last(dquot);
849: }
]] TruncatedOutput:false]
|
| 14/2 |
2026/05/17 13:21 |
llm |
expert |
0m
Model:
Tokens:
input: 10700
output: 39
thoughts: 369
Thoughts: **Analyzing the `dquot_scan_active` Function**
Okay, so I'm looking closely at how `dquot_scan_active` functions and I'm seeing a potential flaw in its logic. Specifically, I'm focusing on the interaction with the `dq_count` field. It looks like the code iterates through the `inuse_list` and, if a dquot is active and on the right superblock, it increments `dq_count` using `atomic_inc`. The key issue here is that this increment happens *without* first removing the dquot from the free or releasing lists, which is usually handled by `remove_free_dquot(dquot)`.
If `dq_count` was initially zero, it suggests the dquot was on either the `free_dquots` or `releasing_dquots` list. So, by incrementing `dq_count` directly, we're leaving the dquot on its respective free/releasing list, while also potentially increasing its usage count. Then after it iterates it calls `dqput(old_dquot)`.
This raises a red flag. I know that dquots on the `inuse_list` can indeed have `dq_count == 0` if `dq_count` had dropped to zero and it was then added to `free_dquots` or `releasing_dquots` while *still* remaining on `inuse_list`. This is expected behavior. However, this function is manipulating `dq_count` and it's not clear that this process is handled properly to prevent double freeing or other race conditions.
I'm thinking I need to double-check the `dqput` implementation to fully understand the implications of this. It's crucial to confirm that `dqput` handles the scenario where a dquot may exist on both `inuse_list` and a free/releasing list. I need to make sure this code is thread-safe and doesn't introduce a memory leak or a corruption.
|
| 15/2 |
2026/05/17 13:21 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/quota/dquot.c IncludeLines:true Name:dqput]
Results: map[SourceCode: 853: /*
854: * Put reference to dquot
855: */
856: void dqput(struct dquot *dquot)
857: {
858: if (!dquot)
859: return;
860: #ifdef CONFIG_QUOTA_DEBUG
861: if (!atomic_read(&dquot->dq_count)) {
862: quota_error(dquot->dq_sb, "trying to free free dquot of %s %d",
863: quotatypes[dquot->dq_id.type],
864: from_kqid(&init_user_ns, dquot->dq_id));
865: BUG();
866: }
867: #endif
868: dqstats_inc(DQST_DROPS);
869:
870: spin_lock(&dq_list_lock);
871: if (atomic_read(&dquot->dq_count) > 1) {
872: /* We have more than one user... nothing to do */
873: atomic_dec(&dquot->dq_count);
874: /* Releasing dquot during quotaoff phase? */
875: if (!sb_has_quota_active(dquot->dq_sb, dquot->dq_id.type) &&
876: atomic_read(&dquot->dq_count) == 1)
877: wake_up(&dquot_ref_wq);
878: spin_unlock(&dq_list_lock);
879: return;
880: }
881:
882: /* Need to release dquot? */
883: WARN_ON_ONCE(!list_empty(&dquot->dq_free));
884: put_releasing_dquots(dquot);
885: atomic_dec(&dquot->dq_count);
886: spin_unlock(&dq_list_lock);
887: queue_delayed_work(quota_unbound_wq, "a_release_work, 1);
888: }
SourceFile:fs/quota/dquot.c]
|
| 16/2 |
2026/05/17 13:21 |
llm |
expert |
0m
Model:
Tokens:
input: 12158
output: 43
thoughts: 235
Thoughts: **Dquot Conundrum**
Okay, so I'm tracing through this dquot code, and something feels off. It looks like when `dquot_scan_active` bumps `dq_count` from zero to one, it leaves the `dquot` structure on the `dq_free` list β which is either `free_dquots` or `releasing_dquots`. That's the setup. Then, `dqput` gets called, and because `dq_count` is now one, it goes down the path that *should* be about releasing the dquot. But here's where it gets interesting.
It hits this check, `WARN_ON_ONCE(!list_empty(&dquot->dq_free));`, and this triggers because the `dquot` is *still* on the `dq_free` list! That's a red flag. From there, it calls `put_releasing_dquots(dquot)`, which then does a `list_add_tail(&dquot->dq_free, &releasing_dquots);`. Wait a second⦠that's going to corrupt the list because `dquot->dq_free` is *already* on a list! We're adding the same element twice.
I'm starting to think there's a missed step in `dquot_scan_active`. Shouldn't it call `remove_free_dquot(dquot)` if `dq_count` was zero before incrementing? Need to revisit `dquot_scan_active` and confirm that behavior. Time for another look...
|
| 17/2 |
2026/05/17 13:21 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/quota/dquot.c IncludeLines:true Name:dquot_scan_active]
Results: map[SourceCode: 628: /* Call callback for every active dquot on given filesystem */
629: int dquot_scan_active(struct super_block *sb,
630: int (*fn)(struct dquot *dquot, unsigned long priv),
631: unsigned long priv)
632: {
633: struct dquot *dquot, *old_dquot = NULL;
634: int ret = 0;
635:
636: WARN_ON_ONCE(!rwsem_is_locked(&sb->s_umount));
637:
638: spin_lock(&dq_list_lock);
639: list_for_each_entry(dquot, &inuse_list, dq_inuse) {
640: if (!dquot_active(dquot))
641: continue;
642: if (dquot->dq_sb != sb)
643: continue;
644: /* Now we have active dquot so we can just increase use count */
645: atomic_inc(&dquot->dq_count);
646: spin_unlock(&dq_list_lock);
647: dqput(old_dquot);
648: old_dquot = dquot;
649: /*
650: * ->release_dquot() can be racing with us. Our reference
651: * protects us from new calls to it so just wait for any
652: * outstanding call and recheck the DQ_ACTIVE_B after that.
653: */
654: wait_on_dquot(dquot);
655: if (dquot_active(dquot)) {
656: ret = fn(dquot, priv);
657: if (ret < 0)
658: goto out;
659: }
660: spin_lock(&dq_list_lock);
661: /* We are safe to continue now because our dquot could not
662: * be moved out of the inuse list while we hold the reference */
663: }
664: spin_unlock(&dq_list_lock);
665: out:
666: dqput(old_dquot);
667: return ret;
668: }
SourceFile:fs/quota/dquot.c]
|
| 18/2 |
2026/05/17 13:21 |
llm |
expert |
0m
Model:
Tokens:
input: 13450
output: 39
thoughts: 109
Thoughts: **Dquot Counting Discrepancy**
Okay, so I've been looking at the dquot code, and it seems like `dquot_scan_active` increments `dq_count` without any check to see if it's currently at zero. That doesn't seem right. It looks like we could be potentially incrementing this counter on dquots that haven't actually been properly allocated.
Hold on, I see something in `dqget` that seems relevant. Specifically, this block:
```c
if (!atomic_read(&dquot->dq_count))
remove_free_dquot(dquot);
atomic_inc(&dquot->dq_count);
```
Ah, right. `dqget` *does* check and call `remove_free_dquot` if the count is zero before incrementing. This means `dquot_scan_active` is indeed missing a crucial check and subsequent call to `remove_free_dquot(dquot)`. I suspect that could lead to memory management issues. We need to verify this assumption through testing. This oversight could be a serious bug.
|
| 19/2 |
2026/05/17 13:22 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/quota/dquot.c IncludeLines:true Name:dqget]
Results: map[SourceCode: 918: /*
919: * Get reference to dquot
920: *
921: * Locking is slightly tricky here. We are guarded from parallel quotaoff()
922: * destroying our dquot by:
923: * a) checking for quota flags under dq_list_lock and
924: * b) getting a reference to dquot before we release dq_list_lock
925: */
926: struct dquot *dqget(struct super_block *sb, struct kqid qid)
927: {
928: unsigned int hashent = hashfn(sb, qid);
929: struct dquot *dquot, *empty = NULL;
930:
931: if (!qid_has_mapping(sb->s_user_ns, qid))
932: return ERR_PTR(-EINVAL);
933:
934: if (!sb_has_quota_active(sb, qid.type))
935: return ERR_PTR(-ESRCH);
936: we_slept:
937: spin_lock(&dq_list_lock);
938: spin_lock(&dq_state_lock);
939: if (!sb_has_quota_active(sb, qid.type)) {
940: spin_unlock(&dq_state_lock);
941: spin_unlock(&dq_list_lock);
942: dquot = ERR_PTR(-ESRCH);
943: goto out;
944: }
945: spin_unlock(&dq_state_lock);
946:
947: dquot = find_dquot(hashent, sb, qid);
948: if (!dquot) {
949: if (!empty) {
950: spin_unlock(&dq_list_lock);
951: empty = get_empty_dquot(sb, qid.type);
952: if (!empty)
953: schedule(); /* Try to wait for a moment... */
954: goto we_slept;
955: }
956: dquot = empty;
957: empty = NULL;
958: dquot->dq_id = qid;
959: /* all dquots go on the inuse_list */
960: put_inuse(dquot);
961: /* hash it first so it can be found */
962: insert_dquot_hash(dquot);
963: spin_unlock(&dq_list_lock);
964: dqstats_inc(DQST_LOOKUPS);
965: } else {
966: if (!atomic_read(&dquot->dq_count))
967: remove_free_dquot(dquot);
968: atomic_inc(&dquot->dq_count);
969: spin_unlock(&dq_list_lock);
970: dqstats_inc(DQST_CACHE_HITS);
971: dqstats_inc(DQST_LOOKUPS);
972: }
973: /* Wait for dq_lock - after this we know that either dquot_release() is
974: * already finished or it will be canceled due to dq_count > 0 test */
975: wait_on_dquot(dquot);
976: /* Read the dquot / allocate space in quota file */
977: if (!dquot_active(dquot)) {
978: int err;
979:
980: err = sb->dq_op->acquire_dquot(dquot);
981: if (err < 0) {
982: dqput(dquot);
983: dquot = ERR_PTR(err);
984: goto out;
985: }
986: }
987: /*
988: * Make sure following reads see filled structure - paired with
989: * smp_mb__before_atomic() in dquot_acquire().
990: */
991: smp_rmb();
992: /* Has somebody invalidated entry under us? */
993: WARN_ON_ONCE(hlist_unhashed(&dquot->dq_hash));
994: out:
995: if (empty)
996: do_destroy_dquot(empty);
997:
998: return dquot;
999: }
SourceFile:fs/quota/dquot.c]
|
| 20/2 |
2026/05/17 13:22 |
llm |
expert |
0m
Model:
Tokens:
input: 15129
output: 51
thoughts: 475
Thoughts: **Analyzing a Critical List Corruption Bug in Dquot Handling**
Okay, so I've pinpointed a bug in `dquot_scan_active`. It looks like it increments `dq_count` without checking if it was initially zero, and crucially, *without* removing the dquot from the `free_dquots` list if `dq_count` *was* zero.
Let me just double-check the code: Yep, right here:
```c
/* Now we have active dquot so we can just increase use count */
atomic_inc(&dquot->dq_count);
```
If I change this to:
```c
if (!atomic_read(&dquot->dq_count))
remove_free_dquot(dquot);
atomic_inc(&dquot->dq_count);
```
Then it should be fixed.
Hold on, if `dquot_scan_active` increments the count but *doesn't* remove from `free_dquots`, then later, when `dqput` is called and `dq_count` goes to zero, it calls `put_releasing_dquots(dquot)`. And what happens in `put_releasing_dquots(dquot)`? It does a `list_add_tail(&dquot->dq_free, &releasing_dquots)`. But the thing is, `dquot->dq_free` is *already* on `free_dquots`!
This means `list_add_tail` is going to corrupt the `free_dquots` and `releasing_dquots` lists. This is a classic list corruption vulnerability. We're talking about arbitrary memory read/write or use-after-free, which is generally exploitable.
Let me assess the impact. A `list_add_tail` on an already linked list node will overwrite `prev` and `next` pointers within the node. It will also modify the `prev` node in the new list. This is a garden-variety list corruption. These types of corruptions are commonly exploited to gain code execution or at least memory corruption.
So, is this exploitable? Absolutely. Yes.
Now, how do we trigger this? `dquot_scan_active` is called from `qsync_work_fn` in `fs/ocfs2/quota_global.c`. I need to verify, is it called from anywhere else?
|
| 21/2 |
2026/05/17 13:22 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:fs/quota/dquot.c IncludeSnippetLines:2 Name:dquot_scan_active SourceTreePrefix:]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:qsync_work_fn SourceFile:fs/ocfs2/quota_global.c SourceLine:658 SourceSnippet: 656: */
657: if (down_read_trylock(&sb->s_umount)) {
658: dquot_scan_active(sb, ocfs2_sync_dquot_helper, oinfo->dqi_type);
659: up_read(&sb->s_umount);
660: }
]] TruncatedOutput:false]
|
| 22/2 |
2026/05/17 13:22 |
llm |
expert |
0m
Model:
Tokens:
input: 16362
output: 45
thoughts: 1263
Thoughts: **OCFS2 Quota Synchronization Vulnerability Analysis**
Okay, so I'm digging into this potential vulnerability within OCFS2's quota synchronization. The code indicates this is called from `qsync_work_fn`, which is a delayed work function running periodically to sync quotas in the OCFS2 cluster file system. So, the question is, can a local unprivileged user trigger this? Let's break this down.
The bug hinges on a `dquot` being on the free list (meaning `dq_count == 0`), but *still* flagged as active (`dquot_active(dquot)` is true). When can a `dquot` be in this weird state? Well, `dqput` is called when all references to a `dquot` are dropped. If `dq_count` hits zero, `put_releasing_dquots(dquot)` is called, queuing `quota_release_work`.
`quota_release_workfn` is responsible for eventually clearing the active flag if the `dquot` is clean, or writing it to disk first and *then* clearing the active flag. Thinking about it, `dquot_active` checks `DQ_ACTIVE_B` in `dq_flags`. If `dq_count` is 0, then the `dquot` is either on `releasing_dquots` or `free_dquots`. If it is on `releasing_dquots`, `quota_release_workfn` will process it. If it's on `free_dquots`, it's been released and is inactive, or is it *still* active? This is where it gets interesting...
Looking at `quota_release_workfn`, it goes like this: first, if the `dquot` is dirty, it commits the `dquot` to disk, but *only* if the reference count is zero. After committing or skipping, it checks to see if the `dquot` is still active by checking the atomic reference count. Then if it *is* active, it will call `release_dquot()`, *then* clear the `DQ_ACTIVE_B` flag. After that, the `dquot` is moved to the free list by removing it from `releasing_dquots`, and `put_dquot_last()` is called.
So, while it is on `releasing_dquots`, it can *absolutely* still have `DQ_ACTIVE_B` set! And `dquot_scan_active` checks `dquot_active(dquot)` which checks `DQ_ACTIVE_B`, so if `dquot_scan_active` runs while a dquot is on `releasing_dquots` (before `quota_release_workfn` clears `DQ_ACTIVE_B`), it will find it, incrementing the reference count from 0 to 1, without removing it from `releasing_dquots`.
Then, critically, `dquot_scan_active` calls `dqput(old_dquot)` (the dquot it just processed). `dqput` decrements `dq_count` from 1 to 0, then calls `put_releasing_dquots(dquot)`, which does `list_add_tail(&dquot->dq_free, &releasing_dquots)`. But that list entry is *already* on `releasing_dquots`! Therefore, `list_add_tail` will corrupt the `releasing_dquots` list. Bingo!
Now, can an unprivileged user exploit this? If a system has an OCFS2 filesystem mounted with quotas, then any user can create and delete files, allocating and freeing dquots. When a user deletes their last file (or the quota is no longer needed), the dquot's reference count drops to zero. `qsync_work_fn` runs periodically. If the timing is right (the `qsync_work_fn` runs while the `dquot` is still on `releasing_dquots`), that will corrupt the list. Now the last question: can an unprivileged user mount OCFS2? Usually mounting OCFS2 needs `CAP_SYS_ADMIN` in the initial namespace, because OCFS2 is not `FS_USERNS_MOUNT`, so we will have to check if the kernel allows it, or if it can be exploited in a different way.
|
| 23/2 |
2026/05/17 13:22 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/ocfs2/super.c IncludeLines:true Name:ocfs2_fs_type]
Results: map[SourceCode:1222: static struct file_system_type ocfs2_fs_type = {
1223: .owner = THIS_MODULE,
1224: .name = "ocfs2",
1225: .kill_sb = kill_block_super,
1226: .fs_flags = FS_REQUIRES_DEV|FS_RENAME_DOES_D_MOVE,
1227: .next = NULL,
1228: .init_fs_context = ocfs2_init_fs_context,
1229: .parameters = ocfs2_param_spec,
1230: };
SourceFile:fs/ocfs2/super.c]
|
| 24/2 |
2026/05/17 13:22 |
llm |
expert |
0m
Model:
Tokens:
input: 18833
output: 20
thoughts: 372
Thoughts: **Analyzing the Accessibility of the Quota Bug**
Okay, so `FS_USERNS_MOUNT` isn't present, which means an unprivileged user can't just spin up a user namespace and mount OCFS2 directly. So, that's one avenue closed. The text says that an unprivileged user *could* trigger the bug if the administrator *has already* mounted an OCFS2 filesystem with quotas. They'd do this by messing with file creation and deletion to mess with dquot refcounts.
Hmm, OCFS2 is a cluster filesystem, right? Enterprise stuff. Is it commonly deployed? Probably not on a typical system. But if it *is* mounted, then an unprivileged user can potentially exploit the bug.
Now, let's go back to the prompt: "Accessible From Unprivileged Processes." It wants to know if a standard user process can trigger this bug without special capabilities or device access. The exploit here seems to rely on an *already* mounted OCFS2 filesystem, which isn't the usual case.
Generally, for these filesystem bugs, if the filesystem can be mounted by an unprivileged user through user namespaces or removable media, it's considered accessible. If it requires root to mount, it's only accessible if the unprivileged process can trigger the bug on an already mounted filesystem AND it's a reasonable assumption that such a filesystem *might* be mounted.
So, in this case, OCFS2 is the specific filesystem. If it's not mounted, the bug is unreachable. That's clear.
But wait a minute... the bug is in `fs/quota/dquot.c` β that's generic quota code, right? So the implications may be more far reaching than just OCFS2? No, wait! `dquot_scan_active` is used in generic quota code but is *only* called by `ocfs2`! Now I have to double check that. Let me make sure that's correct.
|
| 25/2 |
2026/05/17 13:23 |
tool |
grepper |
0m
Args: map[Expression:dquot_scan_active]
Results: map[Output:fs/ocfs2/quota_global.c=645=static void qsync_work_fn(struct work_struct *work)
--
fs/ocfs2/quota_global.c-657- if (down_read_trylock(&sb->s_umount)) {
fs/ocfs2/quota_global.c:658: dquot_scan_active(sb, ocfs2_sync_dquot_helper, oinfo->dqi_type);
fs/ocfs2/quota_global.c-659- up_read(&sb->s_umount);
--
fs/quota/dquot.c=574=static void invalidate_dquots(struct super_block *sb, int type)
--
fs/quota/dquot.c-628-/* Call callback for every active dquot on given filesystem */
fs/quota/dquot.c:629:int dquot_scan_active(struct super_block *sb,
fs/quota/dquot.c-630- int (*fn)(struct dquot *dquot, unsigned long priv),
--
fs/quota/dquot.c-668-}
fs/quota/dquot.c:669:EXPORT_SYMBOL(dquot_scan_active);
fs/quota/dquot.c-670-
--
include/linux/quotaops.h=65=void dqput(struct dquot *dquot);
include/linux/quotaops.h:66:int dquot_scan_active(struct super_block *sb,
include/linux/quotaops.h-67- int (*fn)(struct dquot *dquot, unsigned long priv),
]
|
| 26/2 |
2026/05/17 13:23 |
llm |
expert |
0m
Model:
Tokens:
input: 20069
output: 66
thoughts: 2879
Thoughts: **Vulnerability Analysis: dquot_scan_active in ocfs2 Filesystem**
Okay, let's break this down. It seems this bug hinges specifically on how `ocfs2` utilizes `dquot_scan_active`. The crucial point is that an unprivileged user can exploit it if `ocfs2` is mounted with quotas enabled. We need to be specific and consider the nuances.
"Accessible From Unprivileged Processes" is definitely True. The administrator might need to mount the filesystem, but once it's up, normal file operations by any user can trigger the vulnerability. There's no privileged operation or capability needed for the user, as long as quota is enabled.
I'm also marking "Malicious Filesystem Trigger" as True. If someone can provide a malicious OCFS2 image that's mounted (potentially via USB, or even a network mount), the race condition is exposed. Although, even a *normal* OCFS2 filesystem, when mounted, is sufficient to trigger the vulnerability.
We're looking at a race condition. The vulnerability involves a list corruption in `releasing_dquots` or `free_dquots`. Specifically, `dquot_scan_active` increments `dq_count` of a `dquot` while it's still on one of those free lists. This is the crucial bug. When `dqput` is eventually called, it decrements the count back to zero, and the subsequent `put_releasing_dquots` call corrupts the list. The warning message is a symptom of this corruption, not the root cause. This list corruption then leads to a classic list corruption with the very next line of code, which will be a security issue.
The exploitation scenario is pretty clear: repeated file creation and deletion on a mounted OCFS2 filesystem with quotas enabled. These file operations will allocate and free dquots, which, when racing with `qsync_work_fn`, exposes the bug.
I've verified the `dquot_scan_active` code, and confirmed that the missing `remove_free_dquot` call is indeed the core problem. The fix would involve checking the ref count and *removing* the dquot from the free list before incrementing the ref count. That is likely what would be the patch.
I've grepped the kernel source and can confirm that `dquot_scan_active` is exclusively used by `ocfs2`, making it a filesystem-specific bug, even if the underlying code is in a generic quota function.
Now, let's run through the impact assessment:
* Exploitable: True (List corruption leading to arbitrary memory read/write).
* Denial of Service: True (Kernel crash due to list corruption).
* Accessible From Unprivileged Processes: True (Normal file operations on OCFS2).
* Accessible From User Namespaces: True (Same as above, it doesn't require any capability).
* VM Guest Trigger: False (Not a hypervisor bug).
* VM Host Trigger in the Confidential Computing Context: False.
* Ethernet Network Trigger: False.
* Other Remote Trigger: False.
* Peripheral Trigger: False.
* Malicious Filesystem Trigger: True (Mounting a OCFS2 image, even if not malicious, will trigger).
|
| 27/2 |
2026/05/17 13:23 |
tool |
set-results |
0m
Args: map[DenialOfService:true Exploitable:true FilesystemTrigger:true NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
Results: map[DenialOfService:true Exploitable:true FilesystemTrigger:true NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
|
| 28/2 |
2026/05/17 13:23 |
llm |
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Model:
Tokens:
input: 23792
output: 682
thoughts: 13
Thoughts: Okay, here's the summary, rendered as a first-person thought process, keeping in mind the user is an expert:
**Delivering the Verdict**
Alright, the data's in, the analyses are complete, and the simulations have run their course. Itβs decision time. My task now is to craft a concise and accurate response, a culmination of all the investigation. This isn't just about regurgitating numbers; it's about synthesizing the findings into a clear and defensible conclusion. I need to ensure the final response acknowledges any assumptions made and potential limitations, yet articulates the core insight with precision. It's time to translate the technical into the pragmatic, the abstract into the actionable, ensuring the conclusion is readily understood in the field.
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2026/05/17 13:23 |
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Results: map[Explanation:**Analysis of the Bug**
The warning `WARN_ON_ONCE(!list_empty(&dquot->dq_free))` in `dqput()` is
triggered due to a race condition and list mismanagement in the generic quota
code, specifically within `dquot_scan_active()`.
**Root Cause:**
The function `dquot_scan_active()` in `fs/quota/dquot.c` iterates over the
`inuse_list` of dquots and increments the reference count (`dq_count`) of active
dquots to safely process them. However, it fails to check if the reference count
was previously `0`.
When a dquot's reference count drops to `0`, it is placed on the `free_dquots`
or `releasing_dquots` list via its `dq_free` list head, but it remains on the
`inuse_list`. If `dquot_scan_active()` encounters such a dquot (which can happen
if it races with `dqput()` before the release work clears the `DQ_ACTIVE_B`
flag), it increments `dq_count` from `0` to `1` but **forgets to remove the
dquot from the free/releasing list** (a step correctly handled by `dqget()` via
`remove_free_dquot()`).
When `dquot_scan_active()` finishes processing the dquot, it calls `dqput()`.
`dqput()` decrements the reference count back to `0` and attempts to release the
dquot by calling `put_releasing_dquots()`, which executes
`list_add_tail(&dquot->dq_free, &releasing_dquots)`. Because `dquot->dq_free` is
already linked on a list, this `list_add_tail()` operation corrupts the list
pointers (`prev` and `next`), leading to a classic list corruption
vulnerability. The `WARN_ON_ONCE` is just a symptom of the list corruption that
is about to happen on the very next line.
**Exploitability:**
List corruptions in the Linux kernel are highly dangerous and can typically be
exploited to achieve arbitrary memory read/write primitives, leading to
privilege escalation or memory corruption. Therefore, the bug is marked as
**Exploitable**. It will also easily cause kernel panics, leading to **Denial of
Service**.
**Accessibility:**
The vulnerable function `dquot_scan_active()` is exported but currently only
called by `qsync_work_fn()` in the **OCFS2** filesystem, which runs periodically
to synchronize quotas.
If an OCFS2 filesystem is mounted with quotas enabled, any unprivileged user can
trigger this race condition by repeatedly creating and deleting files (which
allocates and frees dquots), racing with the periodic `qsync_work_fn()` worker.
Thus, it is accessible from **Unprivileged Processes** and **User Namespaces**.
Furthermore, because OCFS2 is a block-based filesystem, the bug can be exposed
by auto-mounting a crafted or normal OCFS2 image from a removable device (e.g.,
USB drive), making it a **Malicious Filesystem Trigger**.]
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