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

Status: moderation: reported on 2026/08/11 00:13
Subsystems: fuse
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+f6e8a3b65040c7c33d77@syzkaller.appspotmail.com
First crash: 6d09h, last: 6d09h
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
dce54491 assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KASAN: slab-use-after-free Read in fuse_dev_do_write 2026/08/08 22:13 2026/08/08 22:13 2026/08/08 22:53 5d63f80b
▶ ▼ Similar bugs (9)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-10 BUG: unable to handle kernel paging request in fuse_dev_do_write 8 18 1126d 1191d 0/2 auto-obsoleted due to no activity on 2023/09/03 17:45
android-54 BUG: unable to handle kernel paging request in fuse_dev_do_write 8 syz, C 213 469d 2065d 0/2 upstream: reported C repro on 2020/12/15 11:21
android-5-15 BUG: unable to handle kernel paging request in fuse_dev_do_write 8 2 1127d 1128d 0/2 auto-obsoleted due to no activity on 2023/10/10 01:15
android-5-15 BUG: unable to handle kernel paging request in fuse_dev_do_write (2) 8 4 229d 252d 0/2 auto-obsoleted due to no activity on 2026/03/25 13:38
android-5-10 BUG: unable to handle kernel paging request in fuse_dev_do_write (4) 8 syz error 150 48d 269d 0/2 premoderation: reported syz repro on 2025/11/15 21:25
android-5-10 BUG: unable to handle kernel paging request in fuse_dev_do_write (2) 8 1 990d 990d 0/2 auto-obsoleted due to no activity on 2024/02/23 07:02
android-6-1 BUG: unable to handle kernel paging request in fuse_dev_do_write origin:downstream 8 syz, C done error 72 43d 1181d 0/2 upstream: reported C repro on 2023/05/18 20:01
android-5-10 BUG: unable to handle kernel paging request in fuse_dev_do_write (3) 8 1 870d 870d 0/2 auto-obsoleted due to no activity on 2024/06/22 11:39
upstream KASAN: slab-out-of-bounds Write in fuse_dev_do_write fuse 21 syz, C 6 349d 354d 29/29 fixed on 2025/10/29 21:02

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in fuse_dev_do_write+0xb54/0xbf0 fs/fuse/dev.c:1940
Read of size 2 at addr ffff88802990801b by task syz.6.1795/14368

CPU: 0 UID: 0 PID: 14368 Comm: syz.6.1795 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
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
 fuse_dev_do_write+0xb54/0xbf0 fs/fuse/dev.c:1940
 fuse_dev_write+0x18c/0x230 fs/fuse/dev.c:1981
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x612/0xba0 fs/read_write.c:687
 ksys_write+0x150/0x270 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f274015e90e
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007f27410d9f68 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f27410da6c0 RCX: 00007f274015e90e
RDX: 0000000000000050 RSI: 0000200000006100 RDI: 0000000000000005
RBP: 0000000000000068 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000005
R13: 0000200000006d80 R14: 00007f2740425fa0 R15: 00007ffc707d4e08
 </TASK>

Allocated by task 14378:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x32d/0x660 mm/slub.c:5489
 _kmalloc_noprof include/linux/slab.h:988 [inline]
 _kzalloc_noprof include/linux/slab.h:1309 [inline]
 fuse_new_init fs/fuse/inode.c:1445 [inline]
 fuse_send_init+0x58/0x820 fs/fuse/inode.c:1506
 vfs_get_super fs/super.c:1273 [inline]
 get_tree_nodev+0xbb/0x150 fs/super.c:1292
 fuse_get_tree+0x29d/0x3b0 fs/fuse/inode.c:1899
 vfs_get_tree+0x92/0x2a0 fs/super.c:1700
 fc_mount fs/namespace.c:1198 [inline]
 do_new_mount_fc fs/namespace.c:3765 [inline]
 do_new_mount+0x319/0xdc0 fs/namespace.c:3841
 do_mount fs/namespace.c:4174 [inline]
 __do_sys_mount fs/namespace.c:4390 [inline]
 __se_sys_mount+0x31d/0x420 fs/namespace.c:4367
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 14378:
 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:2677 [inline]
 slab_free mm/slub.c:6377 [inline]
 kfree+0x1c5/0x640 mm/slub.c:6692
 process_init_reply+0x174/0x21b0 fs/fuse/inode.c:1424
 fuse_send_init+0x506/0x820 fs/fuse/inode.c:1521
 vfs_get_super fs/super.c:1273 [inline]
 get_tree_nodev+0xbb/0x150 fs/super.c:1292
 fuse_get_tree+0x29d/0x3b0 fs/fuse/inode.c:1899
 vfs_get_tree+0x92/0x2a0 fs/super.c:1700
 fc_mount fs/namespace.c:1198 [inline]
 do_new_mount_fc fs/namespace.c:3765 [inline]
 do_new_mount+0x319/0xdc0 fs/namespace.c:3841
 do_mount fs/namespace.c:4174 [inline]
 __do_sys_mount fs/namespace.c:4390 [inline]
 __se_sys_mount+0x31d/0x420 fs/namespace.c:4367
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888029908000
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 27 bytes inside of
 freed 512-byte region [ffff888029908000, ffff888029908200)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x29908
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 ffff88801b001c80 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801b001c80 dead000000000100 dead000000000122
head: 0000000000000000 0000000800100010 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 1, tgid 1 (swapper/0), ts 11745940408, free_ts 11745170687
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1859
 prep_new_page mm/page_alloc.c:1867 [inline]
 get_page_from_freelist+0x21fa/0x2270 mm/page_alloc.c:3946
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5304
 alloc_slab_page mm/slub.c:3266 [inline]
 allocate_slab+0x79/0x5e0 mm/slub.c:3380
 new_slab mm/slub.c:3426 [inline]
 refill_objects+0x2d5/0x350 mm/slub.c:7310
 refill_sheaf mm/slub.c:2804 [inline]
 __pcs_replace_empty_main+0x2bf/0x6b0 mm/slub.c:4675
 alloc_from_pcs mm/slub.c:4773 [inline]
 slab_alloc_node mm/slub.c:4905 [inline]
 __kmalloc_cache_noprof+0x3a7/0x660 mm/slub.c:5485
 _kmalloc_noprof include/linux/slab.h:988 [inline]
 _kzalloc_noprof include/linux/slab.h:1309 [inline]
 device_private_init drivers/base/core.c:3602 [inline]
 device_add+0xb6/0xb80 drivers/base/core.c:3653
 workqueue_sysfs_register+0x12b/0x300 kernel/workqueue.c:7614
 __alloc_workqueue+0x1c75/0x2060 kernel/workqueue.c:5911
 alloc_workqueue_va kernel/workqueue.c:5946 [inline]
 alloc_workqueue_noprof+0xe3/0x210 kernel/workqueue.c:5962
 tty_register_driver+0x2f0/0xdf0 drivers/tty/tty_io.c:3451
 usb_serial_init+0x1e3/0x350 drivers/usb/serial/usb-serial.c:1339
 do_one_initcall+0x250/0x870 init/main.c:1347
 do_initcall_level+0x10a/0x1a0 init/main.c:1409
 do_initcalls+0x59/0xa0 init/main.c:1425
page last free pid 13 tgid 13 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1406 [inline]
 __free_frozen_pages+0xc1e/0xd10 mm/page_alloc.c:2950
 sbitmap_free include/linux/sbitmap.h:188 [inline]
 scsi_device_dev_release+0x5c8/0xee0 drivers/scsi/scsi_sysfs.c:481
 device_release+0xc4/0x1f0 drivers/base/core.c:-1
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x222/0x550 lib/kobject.c:737
 scsi_probe_and_add_lun+0x31cb/0x4b10 drivers/scsi/scsi_scan.c:-1
 __scsi_scan_target+0x1f0/0xe10 drivers/scsi/scsi_scan.c:1797
 scsi_scan_channel drivers/scsi/scsi_scan.c:1885 [inline]
 scsi_scan_host_selected+0x3d3/0x7a0 drivers/scsi/scsi_scan.c:1914
 do_scsi_scan_host drivers/scsi/scsi_scan.c:2047 [inline]
 do_scan_async+0x10e/0x660 drivers/scsi/scsi_scan.c:2057
 async_run_entry_fn+0x9d/0x430 kernel/async.c:129
 process_one_work kernel/workqueue.c:3322 [inline]
 process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 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:
 ffff888029907f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888029907f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888029908000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                            ^
 ffff888029908080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888029908100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/05 17:19 upstream c21bb4193868 b3eac40e .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root KASAN: slab-use-after-free Read in fuse_dev_do_write
* Struck through repros no longer work on HEAD.