[moderation] [fs?] KMSAN: uninit-value in __d_lookup_rcu

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 50897c955902 Merge tag 'linux_kselftest-kunit-fixes-7.1-rc..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12d43ad2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=a9f364ffbbe4c1e9
dashboard link: https://syzkaller.appspot.com/bug?extid=7ff3adde89dd795ad4c4
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
userspace arch: i386
CC: [bra...@kernel.org ja...@suse.cz linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a5addc159c57/disk-50897c95.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/396a470c3768/vmlinux-50897c95.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5bda92abf780/bzImage-50897c95.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7ff3ad...@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in dentry_string_cmp fs/dcache.c:291 [inline]
BUG: KMSAN: uninit-value in dentry_cmp fs/dcache.c:322 [inline]
BUG: KMSAN: uninit-value in __d_lookup_rcu+0x37d/0x5e0 fs/dcache.c:2424
dentry_string_cmp fs/dcache.c:291 [inline]
dentry_cmp fs/dcache.c:322 [inline]
__d_lookup_rcu+0x37d/0x5e0 fs/dcache.c:2424
lookup_fast+0x186/0xa40 fs/namei.c:1849
lookup_fast_for_open fs/namei.c:4548 [inline]
open_last_lookups fs/namei.c:4582 [inline]
path_openat+0xa07/0x64c0 fs/namei.c:4855
do_file_open+0x2aa/0x680 fs/namei.c:4887
do_sys_openat2+0x163/0x370 fs/open.c:1364
do_sys_open fs/open.c:1370 [inline]
__do_sys_openat fs/open.c:1386 [inline]
__se_sys_openat fs/open.c:1381 [inline]
__x64_sys_openat+0x240/0x300 fs/open.c:1381
x64_sys_call+0x2445/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:258
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

<Zero or more stacks not recorded to save memory>

Uninit was stored to memory at:
copy_name fs/dcache.c:2928 [inline]
__d_move+0xf72/0x2aa0 fs/dcache.c:2997
d_move+0x71/0xf0 fs/dcache.c:3044
vfs_rename+0x2510/0x2650 fs/namei.c:6069
filename_renameat2+0xb7f/0x1260 fs/namei.c:6172
__do_sys_rename fs/namei.c:6216 [inline]
__se_sys_rename+0xc5/0x5d0 fs/namei.c:6212
__x64_sys_rename+0x78/0xb0 fs/namei.c:6212
x64_sys_call+0x329/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:83
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
copy_name fs/dcache.c:2928 [inline]
__d_move+0xf72/0x2aa0 fs/dcache.c:2997
d_move+0x71/0xf0 fs/dcache.c:3044
vfs_rename+0x2510/0x2650 fs/namei.c:6069
filename_renameat2+0xb7f/0x1260 fs/namei.c:6172
__do_sys_rename fs/namei.c:6216 [inline]
__se_sys_rename+0xc5/0x5d0 fs/namei.c:6212
__x64_sys_rename+0x78/0xb0 fs/namei.c:6212
x64_sys_call+0x329/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:83
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
copy_name fs/dcache.c:2928 [inline]
__d_move+0xf72/0x2aa0 fs/dcache.c:2997
d_move+0x71/0xf0 fs/dcache.c:3044
vfs_rename+0x2510/0x2650 fs/namei.c:6069
filename_renameat2+0xb7f/0x1260 fs/namei.c:6172
__do_sys_rename fs/namei.c:6216 [inline]
__se_sys_rename+0xc5/0x5d0 fs/namei.c:6212
__x64_sys_rename+0x78/0xb0 fs/namei.c:6212
x64_sys_call+0x329/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:83
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
copy_name fs/dcache.c:2928 [inline]
__d_move+0xf72/0x2aa0 fs/dcache.c:2997
d_move+0x71/0xf0 fs/dcache.c:3044
vfs_rename+0x2510/0x2650 fs/namei.c:6069
filename_renameat2+0xb7f/0x1260 fs/namei.c:6172
__do_sys_rename fs/namei.c:6216 [inline]
__se_sys_rename+0xc5/0x5d0 fs/namei.c:6212
__x64_sys_rename+0x78/0xb0 fs/namei.c:6212
x64_sys_call+0x329/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:83
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
copy_name fs/dcache.c:2928 [inline]
__d_move+0xf72/0x2aa0 fs/dcache.c:2997
d_move+0x71/0xf0 fs/dcache.c:3044
vfs_rename+0x2510/0x2650 fs/namei.c:6069
filename_renameat2+0xb7f/0x1260 fs/namei.c:6172
__do_sys_rename fs/namei.c:6216 [inline]
__se_sys_rename+0xc5/0x5d0 fs/namei.c:6212
__x64_sys_rename+0x78/0xb0 fs/namei.c:6212
x64_sys_call+0x329/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:83
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
copy_name fs/dcache.c:2928 [inline]
__d_move+0xf72/0x2aa0 fs/dcache.c:2997
d_move+0x71/0xf0 fs/dcache.c:3044
vfs_rename+0x2510/0x2650 fs/namei.c:6069
filename_renameat2+0xb7f/0x1260 fs/namei.c:6172
__do_sys_rename fs/namei.c:6216 [inline]
__se_sys_rename+0xc5/0x5d0 fs/namei.c:6212
__x64_sys_rename+0x78/0xb0 fs/namei.c:6212
x64_sys_call+0x329/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:83
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
copy_name fs/dcache.c:2928 [inline]
__d_move+0xf72/0x2aa0 fs/dcache.c:2997
d_move+0x71/0xf0 fs/dcache.c:3044
vfs_rename+0x2510/0x2650 fs/namei.c:6069
filename_renameat2+0xb7f/0x1260 fs/namei.c:6172
__do_sys_rename fs/namei.c:6216 [inline]
__se_sys_rename+0xc5/0x5d0 fs/namei.c:6212
__x64_sys_rename+0x78/0xb0 fs/namei.c:6212
x64_sys_call+0x329/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:83
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
slab_post_alloc_hook mm/slub.c:4576 [inline]
slab_alloc_node mm/slub.c:4898 [inline]
kmem_cache_alloc_lru_noprof+0x37a/0x1260 mm/slub.c:4917
__d_alloc+0x55/0xa00 fs/dcache.c:1807
d_alloc+0x57/0x300 fs/dcache.c:1886
lookup_one_qstr_excl+0x19d/0x7b0 fs/namei.c:1801
__start_renaming+0x38e/0x870 fs/namei.c:3890
filename_renameat2+0x735/0x1260 fs/namei.c:6147
__do_sys_rename fs/namei.c:6216 [inline]
__se_sys_rename+0xc5/0x5d0 fs/namei.c:6212
__x64_sys_rename+0x78/0xb0 fs/namei.c:6212
x64_sys_call+0x329/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:83
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 1 UID: 0 PID: 5899 Comm: udevd Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
=====================================================


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