[v6.1] KASAN: use-after-free Read in gfs2_logd

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f2ddafa93a25 Linux 6.1.166
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=104e4cf6580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b1adc0bfde2d8a4a
dashboard link: https://syzkaller.appspot.com/bug?extid=482d158b4fb80605fb51
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
userspace arch: arm64

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/28fc2cbac5cf/disk-f2ddafa9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b17a5a214fbc/vmlinux-f2ddafa9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c2564b1203e5/Image-f2ddafa9.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+482d15...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in generic_test_bit include/asm-generic/bitops/generic-non-atomic.h:128 [inline]
BUG: KASAN: use-after-free in gfs2_withdrawn fs/gfs2/util.h:208 [inline]
BUG: KASAN: use-after-free in gfs2_logd+0x120/0xbf0 fs/gfs2/log.c:1306
Read of size 8 at addr ffff0000f54bc0a8 by task gfs2_logd/7866

CPU: 1 PID: 7866 Comm: gfs2_logd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/26/2026
Call trace:
dump_backtrace+0x1c0/0x1ec 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
__asan_report_load8_noabort+0x2c/0x38 mm/kasan/report_generic.c:351
generic_test_bit include/asm-generic/bitops/generic-non-atomic.h:128 [inline]
gfs2_withdrawn fs/gfs2/util.h:208 [inline]
gfs2_logd+0x120/0xbf0 fs/gfs2/log.c:1306
kthread+0x250/0x2d8 kernel/kthread.c:376
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:850

Allocated by task 7833:
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]
init_sbd fs/gfs2/ops_fstype.c:77 [inline]
gfs2_fill_super+0x108/0x194c fs/gfs2/ops_fstype.c:1148
get_tree_bdev+0x358/0x544 fs/super.c:1366
gfs2_get_tree+0x54/0x1b4 fs/gfs2/ops_fstype.c:1327
vfs_get_tree+0x90/0x274 fs/super.c:1573
do_new_mount+0x228/0x810 fs/namespace.c:3078
path_mount+0x5bc/0xe80 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+0x49c/0x59c fs/namespace.c:3606
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x58/0x130 arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x128 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

Freed by task 9410:
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4c/0x80 mm/kasan/common.c:53
kasan_save_free_info+0x38/0x5c mm/kasan/generic.c:516
____kasan_slab_free+0x148/0x1b0 mm/kasan/common.c:237
__kasan_slab_free+0x18/0x28 mm/kasan/common.c:245
kasan_slab_free include/linux/kasan.h:177 [inline]
slab_free_hook mm/slub.c:1729 [inline]
slab_free_freelist_hook+0x16c/0x1e8 mm/slub.c:1755
slab_free mm/slub.c:3687 [inline]
__kmem_cache_free+0xbc/0x218 mm/slub.c:3700
kfree+0xd0/0x1a8 mm/slab_common.c:988
free_sbd+0x5c/0x6c fs/gfs2/ops_fstype.c:69
gfs2_put_super+0x6f8/0x760 fs/gfs2/super.c:649
generic_shutdown_super+0x130/0x324 fs/super.c:501
kill_block_super+0x70/0xdc fs/super.c:1470
gfs2_kill_sb+0xc0/0xd4 fs/gfs2/ops_fstype.c:-1
deactivate_locked_super+0xac/0x120 fs/super.c:332
deactivate_super+0xe4/0x104 fs/super.c:363
cleanup_mnt+0x390/0x418 fs/namespace.c:1191
__cleanup_mnt+0x20/0x30 fs/namespace.c:1198
task_work_run+0x1ec/0x278 kernel/task_work.c:203
exit_task_work include/linux/task_work.h:39 [inline]
do_exit+0x550/0x19b0 kernel/exit.c:880
do_group_exit+0x194/0x22c kernel/exit.c:1022
get_signal+0x11cc/0x1304 kernel/signal.c:2871
do_signal arch/arm64/kernel/signal.c:1095 [inline]
do_notify_resume+0x28c/0x2aa4 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_da+0xb4/0x144 arch/arm64/kernel/entry-common.c:516
el0t_64_sync_handler+0x90/0xf0 arch/arm64/kernel/entry-common.c:658
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

The buggy address belongs to the object at ffff0000f54bc000
which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 168 bytes inside of
8192-byte region [ffff0000f54bc000, ffff0000f54be000)

The buggy address belongs to the physical page:
page:000000009d47a21e refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1354b8
head:000000009d47a21e order:3 compound_mapcount:0 compound_pincount:0
flags: 0x5ffc00000010200(slab|head|node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffc00000010200 fffffc0003f43800 dead000000000003 ffff0000c0002c00
raw: 0000000000000000 0000000000020002 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff0000f54bbf80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff0000f54bc000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff0000f54bc080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff0000f54bc100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff0000f54bc180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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