KASAN: slab-use-after-free Read in xfs_defer_item_unpause

Status: upstream: reported on 2026/07/31 02:50
Subsystems: xfs
Labels: prio:normal actionable
[Documentation on labels]
Reported-by: syzbot+e7f24354da9f7915bc54@syzkaller.appspotmail.com
First crash: 52d, last: 2d02h
✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
160540af moderation Actionable: ✅ KASAN: slab-use-after-free Read in xfs_defer_item_unpause 2026/07/31 01:57 2026/07/31 01:57 2026/07/31 02:49 aaffb173
9400c1d6 assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ KASAN: slab-use-after-free Read in xfs_defer_item_unpause 2026/07/27 01:15 2026/07/27 01:15 2026/07/27 01:53 492bab15
Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [xfs?] KASAN: slab-use-after-free Read in xfs_defer_item_unpause 0 (1) 2026/07/31 02:50

Sample crash report:
loop0: detected capacity change from 0 to 32768
=======================================================
WARNING: The mand mount option has been deprecated and
         and is ignored by this kernel. Remove the mand
         option from the mount to silence this warning.
=======================================================
XFS (loop0): Mounting V5 Filesystem bfdc47fc-10d8-4eed-a562-11a831b3f791
XFS (loop0): Ending clean mount
XFS (loop0): Quotacheck needed: Please wait.
XFS (loop0): Quotacheck: Done.
loop0: detected capacity change from 32768 to 0
XFS (loop0): metadata I/O error in "xfs_btree_read_buf_block+0x2ae/0x4a0" at daddr 0x18 len 4 error 5
==================================================================
BUG: KASAN: slab-use-after-free in xfs_defer_item_unpause+0x116/0x250 fs/xfs/libxfs/xfs_defer.c:1256
Read of size 4 at addr ffff88801f5175dc by task syz.0.0/5319

CPU: 0 UID: 0 PID: 5319 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description+0x55/0x1e0 mm/kasan/report.c:378
 print_report+0x58/0x70 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 xfs_defer_item_unpause+0x116/0x250 fs/xfs/libxfs/xfs_defer.c:1256
 xrep_newbt_free+0x3fe/0x5f0 fs/xfs/scrub/newbt.c:520
 xrep_refc_build_new_tree+0x377/0x6d0 fs/xfs/scrub/refcount_repair.c:662
 xrep_refcountbt+0x16b/0x1f0 fs/xfs/scrub/refcount_repair.c:726
 xrep_attempt+0x184/0x7c0 fs/xfs/scrub/repair.c:78
 xfs_scrub_metadata+0xce4/0x1910 fs/xfs/scrub/scrub.c:747
 xfs_ioc_scrubv_metadata+0x7ac/0xb70 fs/xfs/scrub/scrub.c:980
 xfs_file_ioctl+0x916/0x1590 fs/xfs/xfs_ioctl.c:1308
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7b0339e159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f7b0422bfe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f7b03625fa0 RCX: 00007f7b0339e159
RDX: 0000200000000000 RSI: 00000000c0285840 RDI: 0000000000000005
RBP: 00007f7b0343503b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7b03626038 R14: 00007f7b03625fa0 R15: 00007ffe81656b28
 </TASK>

Allocated by task 5319:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 unpoison_slab_object mm/kasan/common.c:340 [inline]
 __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:366
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4683 [inline]
 slab_alloc_node mm/slub.c:4996 [inline]
 kmem_cache_alloc_noprof+0x2b9/0x600 mm/slub.c:5010
 xfs_defer_alloc fs/xfs/libxfs/xfs_defer.c:843 [inline]
 xfs_defer_add+0x143/0x480 fs/xfs/libxfs/xfs_defer.c:871
 xfs_extent_free_defer_add+0x1bf/0x3b0 fs/xfs/xfs_extfree_item.c:507
 xfs_defer_extent_free+0x2a8/0x400 fs/xfs/libxfs/xfs_alloc.c:2682
 xfs_alloc_schedule_autoreap+0xb0/0x170 fs/xfs/libxfs/xfs_alloc.c:2727
 xrep_newbt_add_blocks+0x239/0x410 fs/xfs/scrub/newbt.c:209
 xrep_newbt_alloc_ag_blocks+0x81e/0xcc0 fs/xfs/scrub/newbt.c:309
 xrep_refc_build_new_tree+0x29f/0x6d0 fs/xfs/scrub/refcount_repair.c:619
 xrep_refcountbt+0x16b/0x1f0 fs/xfs/scrub/refcount_repair.c:726
 xrep_attempt+0x184/0x7c0 fs/xfs/scrub/repair.c:78
 xfs_scrub_metadata+0xce4/0x1910 fs/xfs/scrub/scrub.c:747
 xfs_ioc_scrubv_metadata+0x7ac/0xb70 fs/xfs/scrub/scrub.c:980
 xfs_file_ioctl+0x916/0x1590 fs/xfs/xfs_ioctl.c:1308
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 5319:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2748 [inline]
 slab_free mm/slub.c:6508 [inline]
 kmem_cache_free+0x182/0x650 mm/slub.c:6635
 xfs_defer_cancel_list fs/xfs/libxfs/xfs_defer.c:505 [inline]
 xfs_defer_finish_noroll+0xf8b/0x14e0 fs/xfs/libxfs/xfs_defer.c:737
 xfs_defer_finish+0x1c/0x180 fs/xfs/libxfs/xfs_defer.c:755
 xrep_defer_finish+0x16e/0x240 fs/xfs/scrub/repair.c:242
 xrep_newbt_alloc_ag_blocks+0x86c/0xcc0 fs/xfs/scrub/newbt.c:316
 xrep_refc_build_new_tree+0x29f/0x6d0 fs/xfs/scrub/refcount_repair.c:619
 xrep_refcountbt+0x16b/0x1f0 fs/xfs/scrub/refcount_repair.c:726
 xrep_attempt+0x184/0x7c0 fs/xfs/scrub/repair.c:78
 xfs_scrub_metadata+0xce4/0x1910 fs/xfs/scrub/scrub.c:747
 xfs_ioc_scrubv_metadata+0x7ac/0xb70 fs/xfs/scrub/scrub.c:980
 xfs_file_ioctl+0x916/0x1590 fs/xfs/xfs_ioctl.c:1308
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88801f5175a0
 which belongs to the cache xfs_defer_pending of size 64
The buggy address is located 60 bytes inside of
 freed 64-byte region [ffff88801f5175a0, ffff88801f5175e0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff88801f5176c0 pfn:0x1f517
flags: 0xfff00000000200(workingset|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000200 ffff888031719000 ffff888000893ac8 ffff888000893ac8
raw: ffff88801f5176c0 00000002002a0012 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2c40(GFP_NOFS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 12, tgid 12 (kworker/u4:0), ts 93318888580
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1871
 prep_new_page mm/page_alloc.c:1879 [inline]
 get_page_from_freelist+0x2209/0x2280 mm/page_alloc.c:3943
 __alloc_frozen_pages_noprof+0x217/0x5a0 mm/page_alloc.c:5436
 alloc_slab_page mm/slub.c:3347 [inline]
 allocate_slab+0x7d/0x620 mm/slub.c:3462
 new_slab mm/slub.c:3513 [inline]
 refill_objects+0x2d5/0x350 mm/slub.c:7417
 refill_sheaf mm/slub.c:2885 [inline]
 __pcs_replace_empty_main+0x2c8/0x6c0 mm/slub.c:4774
 alloc_from_pcs mm/slub.c:4850 [inline]
 slab_alloc_node mm/slub.c:4984 [inline]
 kmem_cache_alloc_noprof+0x399/0x600 mm/slub.c:5010
 xfs_defer_alloc fs/xfs/libxfs/xfs_defer.c:843 [inline]
 xfs_defer_add+0x143/0x480 fs/xfs/libxfs/xfs_defer.c:871
 xfs_bmap_add_extent_hole_real+0xd61/0x1a40 fs/xfs/libxfs/xfs_bmap.c:2782
 xfs_bmapi_allocate+0x248c/0x2f20 fs/xfs/libxfs/xfs_bmap.c:3975
 xfs_bmapi_write+0x843/0x1330 fs/xfs/libxfs/xfs_bmap.c:4265
 xfs_dquot_disk_alloc+0x4af/0xae0 fs/xfs/xfs_dquot.c:381
 xfs_qm_dqread+0xfe/0x520 fs/xfs/xfs_dquot.c:720
 xfs_qm_dqget+0x18a/0x3d0 fs/xfs/xfs_dquot.c:923
 xfs_qm_quotacheck_dqadjust+0xdd/0x5a0 fs/xfs/xfs_qm.c:1260
 xfs_qm_dqusage_adjust+0x4ad/0x670 fs/xfs/xfs_qm.c:1389
page last free pid 4686 tgid 4686 ts 93222258989 stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 __free_pages_prepare mm/page_alloc.c:1418 [inline]
 __free_frozen_pages+0xc93/0xd90 mm/page_alloc.c:2962
 __slab_free+0x274/0x2c0 mm/slub.c:5823
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x99/0x100 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:350
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4683 [inline]
 slab_alloc_node mm/slub.c:4996 [inline]
 kmem_cache_alloc_node_noprof+0x354/0x610 mm/slub.c:5068
 __alloc_skb+0x1db/0x7a0 net/core/skbuff.c:704
 alloc_skb include/linux/skbuff.h:1384 [inline]
 alloc_skb_with_frags+0xc6/0x760 net/core/skbuff.c:6796
 sock_alloc_send_pskb+0x878/0x990 net/core/sock.c:3015
 unix_dgram_sendmsg+0x4fe/0x1870 net/unix/af_unix.c:2144
 sock_sendmsg_nosec+0x13a/0x180 net/socket.c:800
 __sock_sendmsg net/socket.c:815 [inline]
 __sys_sendto+0x408/0x5a0 net/socket.c:2281
 __do_sys_sendto net/socket.c:2288 [inline]
 __se_sys_sendto net/socket.c:2284 [inline]
 __x64_sys_sendto+0xde/0x100 net/socket.c:2284
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88801f517480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88801f517500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88801f517580: fc fc fc fc fa fb fb fb fb fb fb fb fc fc fc fc
                                                    ^
 ffff88801f517600: fa fb fb fb fb fb fb fb fc fc fc fc fa fb fb fb
 ffff88801f517680: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (12):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/14 04:28 upstream d681d7ef617e 70a60e12 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in xfs_defer_item_unpause
2026/09/04 10:17 upstream 8ab1afb2eb24 801f0966 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in xfs_defer_item_unpause
2026/09/04 10:15 upstream 8ab1afb2eb24 801f0966 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in xfs_defer_item_unpause
2026/09/04 10:09 upstream 8ab1afb2eb24 801f0966 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in xfs_defer_item_unpause
2026/09/04 10:05 upstream 8ab1afb2eb24 801f0966 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in xfs_defer_item_unpause
2026/09/03 16:55 upstream 940de590b839 a8a356ea .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in xfs_defer_item_unpause
2026/09/03 01:53 upstream 940de590b839 6a988719 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in xfs_defer_item_unpause
2026/09/01 20:32 upstream bf1079577a11 587f6b29 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in xfs_defer_item_unpause
2026/08/28 19:14 upstream 818bebeb63dd 41d151d4 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in xfs_defer_item_unpause
2026/08/25 03:17 upstream 818bebeb63dd 614e416a .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in xfs_defer_item_unpause
2026/08/21 02:05 upstream 9d2ed026f031 1e72964b .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in xfs_defer_item_unpause
2026/07/26 01:02 upstream 0ce37745d4bf 492bab15 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in xfs_defer_item_unpause
* Struck through repros no longer work on HEAD.