KASAN: use-after-free Write in gadgetfs_kill_sb

Status: upstream: reported on 2026/10/22 19:31
Reported-by: syzbot+46b9e9ed7cfd8fa24e18@syzkaller.appspotmail.com
First crash: 6d03h, last: 6d03h
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 KASAN: use-after-free Write in gadgetfs_kill_sb 22 1 57d 57d 0/3 upstream: reported on 2026/09/01 15:24
upstream KASAN: use-after-free Write in gadgetfs_kill_sb usb 22 syz, C error 5 1381d 1415d 22/29 fixed on 2023/06/08 14:41
upstream KASAN: slab-use-after-free Write in gadgetfs_kill_sb prio:normal actionable usb 22 C error 5 54d 85d 0/29 upstream: reported C repro on 2026/08/04 02:08

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
BUG: KASAN: use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:176 [inline]
BUG: KASAN: use-after-free in __refcount_sub_and_test include/linux/refcount.h:272 [inline]
BUG: KASAN: use-after-free in __refcount_dec_and_test include/linux/refcount.h:315 [inline]
BUG: KASAN: use-after-free in refcount_dec_and_test include/linux/refcount.h:333 [inline]
BUG: KASAN: use-after-free in put_dev drivers/usb/gadget/legacy/inode.c:159 [inline]
BUG: KASAN: use-after-free in gadgetfs_kill_sb+0x50/0x144 drivers/usb/gadget/legacy/inode.c:2100
Write of size 4 at addr ffff0000efa65840 by task syz.1.696/7245

CPU: 0 PID: 7245 Comm: syz.1.696 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/14/2026
Call trace:
 dump_backtrace+0x1c4/0x1f0 arch/arm64/kernel/stacktrace.c:158
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
 __dump_stack+0x30/0x40 lib/dump_stack.c:88
 dump_stack_lvl+0xf4/0x15c lib/dump_stack.c:106
 print_address_description+0x88/0x218 mm/kasan/report.c:316
 print_report+0x50/0x68 mm/kasan/report.c:420
 kasan_report+0xa8/0xfc mm/kasan/report.c:524
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x258/0x290 mm/kasan/generic.c:189
 __kasan_check_write+0x2c/0x3c mm/kasan/shadow.c:37
 instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:176 [inline]
 __refcount_sub_and_test include/linux/refcount.h:272 [inline]
 __refcount_dec_and_test include/linux/refcount.h:315 [inline]
 refcount_dec_and_test include/linux/refcount.h:333 [inline]
 put_dev drivers/usb/gadget/legacy/inode.c:159 [inline]
 gadgetfs_kill_sb+0x50/0x144 drivers/usb/gadget/legacy/inode.c:2100
 deactivate_locked_super+0xb4/0x128 fs/super.c:332
 deactivate_super+0xe4/0x104 fs/super.c:363
 cleanup_mnt+0x3a8/0x430 fs/namespace.c:1191
 __cleanup_mnt+0x20/0x30 fs/namespace.c:1198
 task_work_run+0x1f4/0x280 kernel/task_work.c:203
 exit_task_work include/linux/task_work.h:39 [inline]
 do_exit+0x54c/0x19ac kernel/exit.c:887
 do_group_exit+0x198/0x238 kernel/exit.c:1030
 get_signal+0x11f4/0x133c kernel/signal.c:2884
 do_signal arch/arm64/kernel/signal.c:1095 [inline]
 do_notify_resume+0x364/0x2c84 arch/arm64/kernel/signal.c:1148
 prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
 exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
 el0_svc+0x9c/0x12c arch/arm64/kernel/entry-common.c:638
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

Allocated by task 5753:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4c/0x80 mm/kasan/common.c:53
 kasan_save_alloc_info+0x24/0x30 mm/kasan/generic.c:505
 ____kasan_kmalloc mm/kasan/common.c:375 [inline]
 __kasan_kmalloc+0xa0/0xb8 mm/kasan/common.c:384
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 kmalloc_trace+0x7c/0x94 mm/slab_common.c:1031
 kmalloc include/linux/slab.h:563 [inline]
 kzalloc include/linux/slab.h:699 [inline]
 dev_new drivers/usb/gadget/legacy/inode.c:170 [inline]
 gadgetfs_fill_super+0x2c0/0x5c0 drivers/usb/gadget/legacy/inode.c:2050
 vfs_get_super fs/super.c:1222 [inline]
 get_tree_single+0xb8/0x170 fs/super.c:1260
 gadgetfs_get_tree+0x28/0x38 drivers/usb/gadget/legacy/inode.c:2081
 vfs_get_tree+0x90/0x278 fs/super.c:1584
 do_new_mount+0x228/0x804 fs/namespace.c:3078
 path_mount+0x5ac/0xe6c fs/namespace.c:3408
 do_mount fs/namespace.c:3421 [inline]
 __do_sys_mount fs/namespace.c:3629 [inline]
 __se_sys_mount fs/namespace.c:3606 [inline]
 __arm64_sys_mount+0x4a0/0x5a0 fs/namespace.c:3606
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x12c arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

The buggy address belongs to the object at ffff0000efa65800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 64 bytes inside of
 1024-byte region [ffff0000efa65800, ffff0000efa65c00)

The buggy address belongs to the physical page:
page:0000000015012b9a refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff0000efa65800 pfn:0x12fa60
head:0000000015012b9a order:3 compound_mapcount:0 compound_pincount:0
flags: 0x5ffc00000010200(slab|head|node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffc00000010200 fffffc0003ece408 fffffc0003373208 ffff0000c0002780
raw: ffff0000efa65800 000000000010000f 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000efa65700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff0000efa65780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff0000efa65800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                           ^
 ffff0000efa65880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff0000efa65900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 7245 at lib/refcount.c:28 refcount_warn_saturate+0x154/0x1f8 lib/refcount.c:28
Modules linked in:
CPU: 1 PID: 7245 Comm: syz.1.696 Tainted: G    B              syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/14/2026
pstate: 62400005 (nZCv daif +PAN -UAO +TCO -DIT -SSBS BTYPE=--)
pc : refcount_warn_saturate+0x154/0x1f8 lib/refcount.c:28
lr : refcount_warn_saturate+0x154/0x1f8 lib/refcount.c:28
sp : ffff8000234e77b0
x29: ffff8000234e77b0 x28: ffff0000c34fe600 x27: ffff0000c34fe600
x26: dfff800000000000 x25: 0000000000000002 x24: 0000000000000002
x23: 0000000000000003 x22: ffff80001da40000 x21: 0000000000000000
x20: ffff0000efa65840 x19: ffff800018dfb000 x18: 1fffe00033c1c97e
x17: 0000000000000000 x16: ffff800008043a58 x15: 0000000000000000
x14: 0000000000000001 x13: 1ffff00002cbda24 x12: 0000000000000000
x11: ff00800008195f68 x10: 0000000000000000 x9 : c07afaad08297e00
x8 : c07afaad08297e00 x7 : 205b5d3536303235 x6 : ffff800008319edc
x5 : 0000000000000000 x4 : 0000000000000001 x3 : 0000000000000000
x2 : ffff8000234e70c0 x1 : 0000000100000000 x0 : 0000000000000000
Call trace:
 refcount_warn_saturate+0x154/0x1f8 lib/refcount.c:28
 __refcount_sub_and_test include/linux/refcount.h:283 [inline]
 __refcount_dec_and_test include/linux/refcount.h:315 [inline]
 refcount_dec_and_test include/linux/refcount.h:333 [inline]
 put_dev drivers/usb/gadget/legacy/inode.c:159 [inline]
 gadgetfs_kill_sb+0x118/0x144 drivers/usb/gadget/legacy/inode.c:2100
 deactivate_locked_super+0xb4/0x128 fs/super.c:332
 deactivate_super+0xe4/0x104 fs/super.c:363
 cleanup_mnt+0x3a8/0x430 fs/namespace.c:1191
 __cleanup_mnt+0x20/0x30 fs/namespace.c:1198
 task_work_run+0x1f4/0x280 kernel/task_work.c:203
 exit_task_work include/linux/task_work.h:39 [inline]
 do_exit+0x54c/0x19ac kernel/exit.c:887
 do_group_exit+0x198/0x238 kernel/exit.c:1030
 get_signal+0x11f4/0x133c kernel/signal.c:2884
 do_signal arch/arm64/kernel/signal.c:1095 [inline]
 do_notify_resume+0x364/0x2c84 arch/arm64/kernel/signal.c:1148
 prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
 exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
 el0_svc+0x9c/0x12c arch/arm64/kernel/entry-common.c:638
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585
irq event stamp: 5079
hardirqs last  enabled at (5079): [<ffff80000825abc0>] raw_spin_rq_unlock_irq kernel/sched/sched.h:1374 [inline]
hardirqs last  enabled at (5079): [<ffff80000825abc0>] finish_lock_switch+0xb0/0x1c8 kernel/sched/core.c:5005
hardirqs last disabled at (5078): [<ffff800011c9de30>] __schedule+0x294/0x1a6c kernel/sched/core.c:6461
softirqs last  enabled at (3698): [<ffff8000081ae3b4>] softirq_handle_end kernel/softirq.c:439 [inline]
softirqs last  enabled at (3698): [<ffff8000081ae3b4>] handle_softirqs+0xb1c/0xc90 kernel/softirq.c:624
softirqs last disabled at (3677): [<ffff800008020e6c>] __do_softirq+0x14/0x20 kernel/softirq.c:630
---[ end trace 0000000000000000 ]---

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/22 19:31 linux-6.1.y 79807e970724 b55fad29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 KASAN: use-after-free Write in gadgetfs_kill_sb
* Struck through repros no longer work on HEAD.