KMSAN: uninit-value in fuse_dentry_revalidate (2)

syzbot Applied syzbot 3 participants 5 messages Feb 15 – Mar 2

Subsystems (2)

VFS FUSE filesystem core

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author syzbot

2026-02-15 08:04 UTC #0 lore raw

Hello,

syzbot found the following issue on:

HEAD commit:    770aaedb461a Merge tag 'bootconfig-v7.0' of git://git.kern..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=158f7e5a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=50148b563a4d5941
dashboard link: https://syzkaller.appspot.com/bug?extid=fdebb2dc960aa56c600a
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=138f7e5a580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13a5c15a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/24ba89b61208/disk-770aaedb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b38352aa3489/vmlinux-770aaedb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c388a7a46371/bzImage-770aaedb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:

Reported-by [email protected]

=====================================================

BUG: KMSAN: uninit-value in fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394
 fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394
 d_revalidate fs/namei.c:1030 [inline]
 lookup_open fs/namei.c:4405 [inline]
 open_last_lookups fs/namei.c:4583 [inline]
 path_openat+0x1614/0x64c0 fs/namei.c:4827
 do_file_open+0x2aa/0x680 fs/namei.c:4859
 do_sys_openat2+0x163/0x380 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_openat fs/open.c:1388 [inline]
 __se_sys_openat fs/open.c:1383 [inline]
 __x64_sys_openat+0x240/0x300 fs/open.c:1383
 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

Uninit was created at:

 slab_post_alloc_hook mm/slub.c:4466 [inline]
 slab_alloc_node mm/slub.c:4788 [inline]
 kmem_cache_alloc_lru_noprof+0x382/0x1280 mm/slub.c:4807
 __d_alloc+0x55/0xa00 fs/dcache.c:1740
 d_alloc_parallel+0x99/0x2740 fs/dcache.c:2604
 lookup_open fs/namei.c:4398 [inline]
 open_last_lookups fs/namei.c:4583 [inline]
 path_openat+0x135f/0x64c0 fs/namei.c:4827
 do_file_open+0x2aa/0x680 fs/namei.c:4859
 do_sys_openat2+0x163/0x380 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_openat fs/open.c:1388 [inline]
 __se_sys_openat fs/open.c:1383 [inline]
 __x64_sys_openat+0x240/0x300 fs/open.c:1383
 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

CPU: 1 UID: 0 PID: 6074 Comm: syz.0.20 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
=====================================================

---
This report is generated by a bot. It may contain errors. See https://goo.gl/tpsmEJ for more information about syzbot. syzbot engineers can be reached at [email protected].

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

Luis Henriques

2026-02-16 10:20 UTC #1 lore raw

Quoted 18 lines · syzbot

Hello,
syzbot found the following issue on:
HEAD commit:    770aaedb461a Merge tag 'bootconfig-v7.0' of git://git.kern..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=158f7e5a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=50148b563a4d5941
dashboard link: https://syzkaller.appspot.com/bug?extid=fdebb2dc960aa56c600a
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=138f7e5a580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13a5c15a580000
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/24ba89b61208/disk-770aaedb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b38352aa3489/vmlinux-770aaedb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c388a7a46371/bzImage-770aaedb.xz

Quoted 5 lines

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by [email protected]
=====================================================
BUG: KMSAN: uninit-value in fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394

This seems to point here:

	if (entry->d_time < atomic_read(&fc->epoch))
		goto invalid;

which means that the following initialisation is missing:

fs/fuse/dir.c +1 -0

index f25ee47822ad..2ce306e35be3 100644
@@ -481,6 +481,7 @@ static int fuse_dentry_init(struct dentry *dentry)
 	fd->dentry = dentry;
 	RB_CLEAR_NODE(&fd->node);
 	dentry->d_fsdata = fd;
+	dentry->d_time = 0;
 
 	return 0;
 }

Or maybe should that be done in __d_alloc() instead?

Cheers,

Signature · 1 line

Luís

Quoted 66 lines

 fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394
 d_revalidate fs/namei.c:1030 [inline]
 lookup_open fs/namei.c:4405 [inline]
 open_last_lookups fs/namei.c:4583 [inline]
 path_openat+0x1614/0x64c0 fs/namei.c:4827
 do_file_open+0x2aa/0x680 fs/namei.c:4859
 do_sys_openat2+0x163/0x380 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_openat fs/open.c:1388 [inline]
 __se_sys_openat fs/open.c:1383 [inline]
 __x64_sys_openat+0x240/0x300 fs/open.c:1383
 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
Uninit was created at:
 slab_post_alloc_hook mm/slub.c:4466 [inline]
 slab_alloc_node mm/slub.c:4788 [inline]
 kmem_cache_alloc_lru_noprof+0x382/0x1280 mm/slub.c:4807
 __d_alloc+0x55/0xa00 fs/dcache.c:1740
 d_alloc_parallel+0x99/0x2740 fs/dcache.c:2604
 lookup_open fs/namei.c:4398 [inline]
 open_last_lookups fs/namei.c:4583 [inline]
 path_openat+0x135f/0x64c0 fs/namei.c:4827
 do_file_open+0x2aa/0x680 fs/namei.c:4859
 do_sys_openat2+0x163/0x380 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_openat fs/open.c:1388 [inline]
 __se_sys_openat fs/open.c:1383 [inline]
 __x64_sys_openat+0x240/0x300 fs/open.c:1383
 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

CPU: 1 UID: 0 PID: 6074 Comm: syz.0.20 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
=====================================================
---
This report is generated by a bot. It may contain errors. See https://goo.gl/tpsmEJ for more information about syzbot. syzbot engineers can be reached at [email protected].
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.
If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)
If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report
If you want to undo deduplication, reply with:
#syz undup

syzbot

author syzbot

2026-02-16 11:16 UTC #2 lore raw

Forwarded: Re: [syzbot] [fuse?] KMSAN: uninit-value in fuse_dentry_revalidate (2)

In reply to syzbot

For archival purposes, forwarding an incoming command email to [email protected], [email protected].

***

Subject: Re: [syzbot] [fuse?] KMSAN: uninit-value in fuse_dentry_revalidate (2)
Author: [email protected]

Quoted 83 lines · syzbot

Hello,
syzbot found the following issue on:
HEAD commit:    770aaedb461a Merge tag 'bootconfig-v7.0' of git://git.kern..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=158f7e5a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=50148b563a4d5941
dashboard link: https://syzkaller.appspot.com/bug?extid=fdebb2dc960aa56c600a
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=138f7e5a580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13a5c15a580000
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/24ba89b61208/disk-770aaedb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b38352aa3489/vmlinux-770aaedb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c388a7a46371/bzImage-770aaedb.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by [email protected]
=====================================================
BUG: KMSAN: uninit-value in fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394
 fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394
 d_revalidate fs/namei.c:1030 [inline]
 lookup_open fs/namei.c:4405 [inline]
 open_last_lookups fs/namei.c:4583 [inline]
 path_openat+0x1614/0x64c0 fs/namei.c:4827
 do_file_open+0x2aa/0x680 fs/namei.c:4859
 do_sys_openat2+0x163/0x380 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_openat fs/open.c:1388 [inline]
 __se_sys_openat fs/open.c:1383 [inline]
 __x64_sys_openat+0x240/0x300 fs/open.c:1383
 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
Uninit was created at:
 slab_post_alloc_hook mm/slub.c:4466 [inline]
 slab_alloc_node mm/slub.c:4788 [inline]
 kmem_cache_alloc_lru_noprof+0x382/0x1280 mm/slub.c:4807
 __d_alloc+0x55/0xa00 fs/dcache.c:1740
 d_alloc_parallel+0x99/0x2740 fs/dcache.c:2604
 lookup_open fs/namei.c:4398 [inline]
 open_last_lookups fs/namei.c:4583 [inline]
 path_openat+0x135f/0x64c0 fs/namei.c:4827
 do_file_open+0x2aa/0x680 fs/namei.c:4859
 do_sys_openat2+0x163/0x380 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_openat fs/open.c:1388 [inline]
 __se_sys_openat fs/open.c:1383 [inline]
 __x64_sys_openat+0x240/0x300 fs/open.c:1383
 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

CPU: 1 UID: 0 PID: 6074 Comm: syz.0.20 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
=====================================================
---
This report is generated by a bot. It may contain errors. See https://goo.gl/tpsmEJ for more information about syzbot. syzbot engineers can be reached at [email protected].
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.
If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

Quoted 6 lines

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report
If you want to undo deduplication, reply with:
#syz undup

#syz test

fs/fuse/dir.c +1 -0

index f25ee47822ad..2ce306e35be3 100644
@@ -481,6 +481,7 @@ static int fuse_dentry_init(struct dentry *dentry)
 	fd->dentry = dentry;
 	RB_CLEAR_NODE(&fd->node);
 	dentry->d_fsdata = fd;
+	dentry->d_time = 0;
 
 	return 0;
 }

Luis Henriques

2026-02-16 14:48 UTC #3 lore raw

PATCH 1/1 fuse: fix uninit-value in fuse_dentry_revalidate()

In reply to syzbot

fuse_dentry_revalidate() may be called with a dentry that didn't had ->d_time initialised. The issue was found with KMSAN, where lookup_open() calls __d_alloc(), followed by d_revalidate(), as shown below:

=====================================================

BUG: KMSAN: uninit-value in fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394
 fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394
 d_revalidate fs/namei.c:1030 [inline]
 lookup_open fs/namei.c:4405 [inline]
 open_last_lookups fs/namei.c:4583 [inline]
 path_openat+0x1614/0x64c0 fs/namei.c:4827
 do_file_open+0x2aa/0x680 fs/namei.c:4859

[...]

Uninit was created at:

 slab_post_alloc_hook mm/slub.c:4466 [inline]
 slab_alloc_node mm/slub.c:4788 [inline]
 kmem_cache_alloc_lru_noprof+0x382/0x1280 mm/slub.c:4807
 __d_alloc+0x55/0xa00 fs/dcache.c:1740
 d_alloc_parallel+0x99/0x2740 fs/dcache.c:2604
 lookup_open fs/namei.c:4398 [inline]
 open_last_lookups fs/namei.c:4583 [inline]
 path_openat+0x135f/0x64c0 fs/namei.c:4827
 do_file_open+0x2aa/0x680 fs/namei.c:4859

[...]
=====================================================

Reported-by [email protected]

Closes https://lore.kernel.org/all/[email protected] open here

Fixes 2396356a945b ("fuse: add more control over cache invalidation behaviour")

Signed-off-by Luis Henriques <[email protected]>

---
 fs/fuse/dir.c | 5 +++++
 1 file changed, 5 insertions(+)

fs/fuse/dir.c +5 -0

index f25ee47822ad..66f0113ddfaf 100644
@@ -481,6 +481,11 @@ static int fuse_dentry_init(struct dentry *dentry)
 	fd->dentry = dentry;
 	RB_CLEAR_NODE(&fd->node);
 	dentry->d_fsdata = fd;
+	/*
+	 * Initialising d_time (epoch) to '0' ensures the dentry is invalid
+	 * if compared to fc->epoch, which is initialized to '1'.
+	 */
+	dentry->d_time = 0;
 
 	return 0;
 }

Miklos Szeredi

maintainer Applied

2026-03-02 15:30 UTC #4 lore raw

Re: [PATCH] fuse: fix uninit-value in fuse_dentry_revalidate()

Quoted 25 lines · Luis Henriques

=====================================================

BUG: KMSAN: uninit-value in fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394
 fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394
 d_revalidate fs/namei.c:1030 [inline]
 lookup_open fs/namei.c:4405 [inline]
 open_last_lookups fs/namei.c:4583 [inline]
 path_openat+0x1614/0x64c0 fs/namei.c:4827
 do_file_open+0x2aa/0x680 fs/namei.c:4859

[...]

Uninit was created at:

 slab_post_alloc_hook mm/slub.c:4466 [inline]
 slab_alloc_node mm/slub.c:4788 [inline]
 kmem_cache_alloc_lru_noprof+0x382/0x1280 mm/slub.c:4807
 __d_alloc+0x55/0xa00 fs/dcache.c:1740
 d_alloc_parallel+0x99/0x2740 fs/dcache.c:2604
 lookup_open fs/namei.c:4398 [inline]
 open_last_lookups fs/namei.c:4583 [inline]
 path_openat+0x135f/0x64c0 fs/namei.c:4827
 do_file_open+0x2aa/0x680 fs/namei.c:4859

Quoted 7 lines

[...]
=====================================================
Reported-by [email protected]
Closes https://lore.kernel.org/all/[email protected] open here
Fixes 2396356a945b ("fuse: add more control over cache invalidation behaviour")
Signed-off-by Luis Henriques <[email protected]>

Applied, thanks.

Miklos