[v5.15] KASAN: slab-out-of-bounds Read in kernfs_find_ns

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 29e53a5b1c4f Linux 5.15.194
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=14785b34580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e1bb6d24ef2164eb
dashboard link: https://syzkaller.appspot.com/bug?extid=1cf51b6632b24303a322
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8cd4e3ff852c/disk-29e53a5b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/21e1f773622c/vmlinux-29e53a5b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8f418c0a25cc/bzImage-29e53a5b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1cf51b...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in kernfs_name_compare fs/kernfs/dir.c:326 [inline]
BUG: KASAN: slab-out-of-bounds in kernfs_find_ns+0x473/0x510 fs/kernfs/dir.c:827
Read of size 4 at addr ffff88805570afe0 by task syz.1.3130/16047

CPU: 1 PID: 16047 Comm: syz.1.3130 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
<TASK>
dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
print_address_description+0x60/0x2d0 mm/kasan/report.c:248
__kasan_report mm/kasan/report.c:434 [inline]
kasan_report+0xdf/0x130 mm/kasan/report.c:451
kernfs_name_compare fs/kernfs/dir.c:326 [inline]
kernfs_find_ns+0x473/0x510 fs/kernfs/dir.c:827
kernfs_remove_by_name_ns+0x37/0x100 fs/kernfs/dir.c:1563
remove_bind_files drivers/base/bus.c:550 [inline]
bus_remove_driver+0x89/0x230 drivers/base/bus.c:674
comedi_device_detach_locked+0x16e/0x710 drivers/comedi/drivers.c:207
do_devconfig_ioctl drivers/comedi/comedi_fops.c:844 [inline]
comedi_unlocked_ioctl+0xd0b/0x1050 drivers/comedi/comedi_fops.c:2173
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fa0b13f9ec9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fa0af661038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fa0b1650fa0 RCX: 00007fa0b13f9ec9
RDX: 0000000000000000 RSI: 0000000040946400 RDI: 0000000000000003
RBP: 00007fa0b147cf91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa0b1651038 R14: 00007fa0b1650fa0 R15: 00007fff1c5b88e8
</TASK>

Allocated by task 15631:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track mm/kasan/common.c:46 [inline]
set_alloc_info mm/kasan/common.c:434 [inline]
____kasan_kmalloc mm/kasan/common.c:513 [inline]
__kasan_kmalloc+0xb5/0xf0 mm/kasan/common.c:522
kmalloc include/linux/slab.h:604 [inline]
kzalloc include/linux/slab.h:735 [inline]
uevent_net_init+0xc3/0x2b0 lib/kobject_uevent.c:781
ops_init+0x357/0x600 net/core/net_namespace.c:138
setup_net+0x38d/0x9f0 net/core/net_namespace.c:333
copy_net_ns+0x348/0x5b0 net/core/net_namespace.c:503
create_new_namespaces+0x3d3/0x6f0 kernel/nsproxy.c:110
unshare_nsproxy_namespaces+0x116/0x160 kernel/nsproxy.c:226
ksys_unshare+0x4bc/0x890 kernel/fork.c:3175
__do_sys_unshare kernel/fork.c:3249 [inline]
__se_sys_unshare kernel/fork.c:3247 [inline]
__x64_sys_unshare+0x34/0x40 kernel/fork.c:3247
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0

The buggy address belongs to the object at ffff88805570afc0
which belongs to the cache kmalloc-32 of size 32
The buggy address is located 0 bytes to the right of
32-byte region [ffff88805570afc0, ffff88805570afe0)
The buggy address belongs to the page:
page:ffffea000155c280 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88805570ab40 pfn:0x5570a
flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000200 ffffea0000a8ac08 ffffea000092eec8 ffff888016841500
raw: ffff88805570ab40 000000000040003f 00000001ffffffff 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 0x112cc0(GFP_USER|__GFP_NOWARN|__GFP_NORETRY), pid 8908, ts 403272410893, free_ts 403155659506
prep_new_page mm/page_alloc.c:2426 [inline]
get_page_from_freelist+0x1b77/0x1c60 mm/page_alloc.c:4192
__alloc_pages+0x1e1/0x470 mm/page_alloc.c:5487
alloc_slab_page mm/slub.c:1780 [inline]
allocate_slab mm/slub.c:1917 [inline]
new_slab+0xc0/0x4b0 mm/slub.c:1980
___slab_alloc+0x81e/0xdf0 mm/slub.c:3013
__slab_alloc mm/slub.c:3100 [inline]
slab_alloc_node mm/slub.c:3191 [inline]
slab_alloc mm/slub.c:3233 [inline]
kmem_cache_alloc_trace+0x1a5/0x2a0 mm/slub.c:3250
kmalloc include/linux/slab.h:604 [inline]
__memcg_init_list_lru_node mm/list_lru.c:339 [inline]
memcg_init_list_lru_node mm/list_lru.c:362 [inline]
memcg_init_list_lru mm/list_lru.c:440 [inline]
__list_lru_init+0x50a/0xa50 mm/list_lru.c:607
alloc_super+0x76c/0x950 fs/super.c:272
sget+0x1ca/0x440 fs/super.c:637
mount_bdev+0xec/0x3c0 fs/super.c:1373
legacy_get_tree+0xe6/0x180 fs/fs_context.c:611
vfs_get_tree+0x88/0x270 fs/super.c:1530
do_new_mount+0x24a/0xa40 fs/namespace.c:3025
do_mount fs/namespace.c:3368 [inline]
__do_sys_mount fs/namespace.c:3576 [inline]
__se_sys_mount+0x2d6/0x3c0 fs/namespace.c:3553
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1340 [inline]
free_pcp_prepare mm/page_alloc.c:1391 [inline]
free_unref_page_prepare+0x637/0x6c0 mm/page_alloc.c:3317
free_unref_page+0x94/0x280 mm/page_alloc.c:3396
put_page include/linux/mm.h:1258 [inline]
af_alg_free_areq_sgls crypto/af_alg.c:685 [inline]
af_alg_free_resources+0x3cd/0x650 crypto/af_alg.c:1057
_skcipher_recvmsg crypto/algif_skcipher.c:144 [inline]
skcipher_recvmsg+0xa65/0xd40 crypto/algif_skcipher.c:157
____sys_recvmsg+0x291/0x580 net/socket.c:-1
___sys_recvmsg+0x1af/0x4f0 net/socket.c:2697
__sys_recvmsg net/socket.c:2727 [inline]
__do_sys_recvmsg net/socket.c:2737 [inline]
__se_sys_recvmsg net/socket.c:2734 [inline]
__x64_sys_recvmsg+0x1dd/0x2a0 net/socket.c:2734
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0

Memory state around the buggy address:
ffff88805570ae80: fa fb fb fb fc fc fc fc fa fb fb fb fc fc fc fc
ffff88805570af00: fa fb fb fb fc fc fc fc 00 00 00 fc fc fc fc fc
>ffff88805570af80: fa fb fb fb fc fc fc fc 00 00 00 fc fc fc fc fc
^
ffff88805570b000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88805570b080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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