KASAN: slab-out-of-bounds Read in ctl_ioctl

Status: upstream: reported C repro on 2026/09/18 20:17
Subsystems: dm
Labels: prio:normal
[Documentation on labels]
Reported-by: syzbot+48d935cf48a4a76be346@syzkaller.appspotmail.com
Fix commit: 9b3fcf519d37 dm ioctl: don't let data_start run past the buffer
Patched on: [ci-qemu-gce-upstream-auto ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm32 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-qemu2-arm64-mte ci-snapshot-upstream-root ci-upstream-gce-leak ci-upstream-kasan-badwrites-root ci-upstream-kasan-gce ci-upstream-kasan-gce-386 ci-upstream-kasan-gce-root ci-upstream-kasan-gce-selinux-root ci-upstream-kasan-gce-smack-root ci-upstream-linux-next-kasan-gce-root ci-upstream-net-kasan-gce ci-upstream-net-this-kasan-gce ci-upstream-rust-kasan-gce ci2-upstream-fs ci2-upstream-kcsan-gce], missing on: [ci-qemu-native-arm64-kvm ci-qemu2-riscv64 ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-gce-arm64 ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root ci2-upstream-usb]
First crash: 21d, last: 6d21h
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
2cf5c62b assessment-security DenialOfService: ❌ Exploitable: ✅ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KASAN: slab-out-of-bounds Read in ctl_ioctl 2026/09/19 01:09 2026/09/19 01:09 2026/09/19 01:58 853b104b
▶ ▼ Discussions (2)
Title Replies (including bot) Last reply
[PATCH] dm ioctl: don't let data_start run past the buffer 3 (3) 2026/09/22 20:13
[syzbot] [dm?] KASAN: slab-out-of-bounds Read in ctl_ioctl 0 (1) 2026/09/18 20:17
▶ ▼ Last patch testing requests (3)
Created Duration User Patch Repo Result
2026/10/02 19:06 12m retest repro upstream report job log log
2026/10/02 19:06 13m retest repro upstream report job log log
2026/10/02 19:06 13m retest repro upstream report job log log

Sample crash report:
==================================================================
BUG: KASAN: slab-out-of-bounds in instrument_copy_to_user include/linux/instrumented.h:129 [inline]
BUG: KASAN: slab-out-of-bounds in _inline_copy_to_user include/linux/uaccess.h:201 [inline]
BUG: KASAN: slab-out-of-bounds in _copy_to_user+0x93/0xd0 lib/usercopy.c:24
Read of size 312 at addr ffff8880511e2c00 by task syz.0.17/5924

CPU: 3 UID: 0 PID: 5924 Comm: syz.0.17 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 lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x13d/0x4b0 mm/kasan/report.c:482
 kasan_report+0xdf/0x1c0 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:186 [inline]
 kasan_check_range+0x10f/0x1e0 mm/kasan/generic.c:200
 instrument_copy_to_user include/linux/instrumented.h:129 [inline]
 _inline_copy_to_user include/linux/uaccess.h:201 [inline]
 _copy_to_user+0x93/0xd0 lib/usercopy.c:24
 copy_to_user include/linux/uaccess.h:230 [inline]
 ctl_ioctl+0x5c2/0xcc0 drivers/md/dm-ioctl.c:2225
 dm_ctl_ioctl+0x22/0x30 drivers/md/dm-ioctl.c:2235
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0a62b9e159
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:00007fff4ea84718 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f0a62e25fa0 RCX: 00007f0a62b9e159
RDX: 0000200000000000 RSI: 00000000c138fd02 RDI: 0000000000000003
RBP: 00007f0a62c3506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0a62e25fac R14: 00007f0a62e25fa0 R15: 00007f0a62e25fa0
 </TASK>

Allocated by task 5924:
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __do_kmalloc_node mm/slub.c:5414 [inline]
 __kvmalloc_node_noprof+0x35b/0x9b0 mm/slub.c:7014
 copy_params drivers/md/dm-ioctl.c:2098 [inline]
 ctl_ioctl+0x944/0xcc0 drivers/md/dm-ioctl.c:2202
 dm_ctl_ioctl+0x22/0x30 drivers/md/dm-ioctl.c:2235
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff8880511e2c00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 allocated 305-byte region [ffff8880511e2c00, ffff8880511e2d31)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x511e0
head: order:2 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801c042c80 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801c042c80 dead000000000100 dead000000000122
head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000002 ffffffffffffff01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000004
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5135, tgid 5135 (udevd), ts 53647527683
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0xfd/0x120 mm/page_alloc.c:1871
 prep_new_page mm/page_alloc.c:1879 [inline]
 get_page_from_freelist+0x110d/0x35d0 mm/page_alloc.c:3943
 __alloc_frozen_pages_noprof+0x2eb/0x3300 mm/page_alloc.c:5436
 alloc_slab_page mm/slub.c:3347 [inline]
 allocate_slab mm/slub.c:3462 [inline]
 new_slab+0xa9/0x6e0 mm/slub.c:3513
 refill_objects+0xe3/0x410 mm/slub.c:7417
 refill_sheaf mm/slub.c:2885 [inline]
 __pcs_replace_empty_main+0x35e/0x650 mm/slub.c:4774
 alloc_from_pcs mm/slub.c:4850 [inline]
 slab_alloc_node mm/slub.c:4984 [inline]
 __kmalloc_cache_noprof+0x4f4/0x6d0 mm/slub.c:5559
 _kmalloc_noprof include/linux/slab.h:991 [inline]
 _kzalloc_noprof include/linux/slab.h:1312 [inline]
 kernfs_fop_open+0x23d/0xd50 fs/kernfs/file.c:634
 do_dentry_open+0x6ab/0x14d0 fs/open.c:996
 vfs_open+0x82/0x3f0 fs/open.c:1101
 do_open fs/namei.c:4837 [inline]
 path_openat+0x19fa/0x2440 fs/namei.c:5000
 do_file_open+0x20e/0x430 fs/namei.c:5029
 do_sys_openat2+0x10f/0x1e0 fs/open.c:1417
 do_sys_open fs/open.c:1423 [inline]
 __do_sys_openat fs/open.c:1439 [inline]
 __se_sys_openat fs/open.c:1434 [inline]
 __x64_sys_openat+0x12d/0x210 fs/open.c:1434
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 12 tgid 12 ts 52862857394 stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 __free_pages_prepare mm/page_alloc.c:1418 [inline]
 __free_pages_ok+0x73b/0x1050 mm/page_alloc.c:1596
 fq_reset include/net/fq_impl.h:386 [inline]
 ieee80211_txq_teardown_flows+0x16f/0x280 net/mac80211/tx.c:1656
 ieee80211_unregister_hw+0x5d/0x360 net/mac80211/main.c:1723
 mac80211_hwsim_del_radio drivers/net/wireless/virtual/mac80211_hwsim_main.c:6256 [inline]
 hwsim_exit_net+0x891/0x1500 drivers/net/wireless/virtual/mac80211_hwsim_main.c:7269
 ops_exit_list net/core/net_namespace.c:200 [inline]
 ops_undo_list+0x2ee/0xab0 net/core/net_namespace.c:253
 cleanup_net+0x499/0x920 net/core/net_namespace.c:706
 process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
 process_scheduled_works kernel/workqueue.c:3479 [inline]
 worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
 kthread+0x373/0x450 kernel/kthread.c:436
 ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
 ffff8880511e2c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8880511e2c80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8880511e2d00: 00 00 00 00 00 00 01 fc fc fc fc fc fc fc fc fc
                                     ^
 ffff8880511e2d80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880511e2e00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/18 18:49 upstream 5dd1818b15d9 853b104b .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: slab-out-of-bounds Read in ctl_ioctl
2026/09/18 18:12 upstream 5dd1818b15d9 853b104b .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: slab-out-of-bounds Read in ctl_ioctl
2026/09/18 17:42 upstream 5dd1818b15d9 853b104b .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: slab-out-of-bounds Read in ctl_ioctl
2026/09/18 17:10 upstream 5dd1818b15d9 853b104b .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: slab-out-of-bounds Read in ctl_ioctl
* Struck through repros no longer work on HEAD.