[syzbot] [fuse?] KMSAN: uninit-value in fuse_fileattr_get

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 18f7fcd5e69a Linux 6.19-rc8
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16bafc5a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=9682a42d8ec8b05c
dashboard link: https://syzkaller.appspot.com/bug?extid=7c31755f2cea07838b0c
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=1329b322580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=178a425a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c8e19a1c3a97/disk-18f7fcd5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ffdc9733836e/vmlinux-18f7fcd5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8cdf30f0d2d2/bzImage-18f7fcd5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7c3175...@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in fuse_fileattr_get+0xeb4/0x1450 fs/fuse/ioctl.c:517
fuse_fileattr_get+0xeb4/0x1450 fs/fuse/ioctl.c:517
vfs_fileattr_get fs/file_attr.c:94 [inline]
__do_sys_file_getattr fs/file_attr.c:416 [inline]
__se_sys_file_getattr+0x6cb/0xbd0 fs/file_attr.c:372
__x64_sys_file_getattr+0xe4/0x150 fs/file_attr.c:372
x64_sys_call+0x17cd/0x3e70 arch/x86/include/generated/asm/syscalls_64.h:469
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc9/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable fa.i created at:
__do_sys_file_getattr fs/file_attr.c:380 [inline]
__se_sys_file_getattr+0x8c/0xbd0 fs/file_attr.c:372
__x64_sys_file_getattr+0xe4/0x150 fs/file_attr.c:372

CPU: 1 UID: 0 PID: 6065 Comm: syz.0.18 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
=====================================================


---
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 syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
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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:
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(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

[Qing Wang]

#syz test

diff --git a/fs/file_attr.c b/fs/file_attr.c
index 13cdb31a3e94..4f514e487e35 100644
--- a/fs/file_attr.c
+++ b/fs/file_attr.c
@@ -413,6 +413,7 @@ SYSCALL_DEFINE5(file_getattr, int, dfd, const char __user *, filename,
return error;
}

+ memset(&fa, 0, sizeof(struct file_kattr));
error = vfs_fileattr_get(filepath.dentry, &fa);
if (error == -ENOIOCTLCMD || error == -ENOTTY)
error = -EOPNOTSUPP;

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+7c3175...@syzkaller.appspotmail.com
Tested-by: syzbot+7c3175...@syzkaller.appspotmail.com

Tested on:

commit: 06bc4e26 Merge tag 'block-6.19-20260205' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1498e402580000

kernel config: https://syzkaller.appspot.com/x/.config?x=9682a42d8ec8b05c
dashboard link: https://syzkaller.appspot.com/bug?extid=7c31755f2cea07838b0c
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=17f0e402580000

Note: testing is done by a robot and is best-effort only.

[Edward Adam Davis]

#syz test

diff --git a/fs/file_attr.c b/fs/file_attr.c

index 13cdb31a3e94..4889cf59b256 100644
--- a/fs/file_attr.c
+++ b/fs/file_attr.c
@@ -377,7 +377,7 @@ SYSCALL_DEFINE5(file_getattr, int, dfd, const char __user *, filename,
struct filename *name __free(putname) = NULL;
unsigned int lookup_flags = 0;
struct file_attr fattr;
- struct file_kattr fa;
+ struct file_kattr fa = { .flags_valid = true }; /* hint only */
int error;

BUILD_BUG_ON(sizeof(struct file_attr) < FILE_ATTR_SIZE_VER0);

[Qing Wang]

#syz test

diff --git a/fs/file_attr.c b/fs/file_attr.c

index 13cdb31a3e94..8b5565cbccb0 100644

--- a/fs/file_attr.c
+++ b/fs/file_attr.c
@@ -377,7 +377,7 @@ SYSCALL_DEFINE5(file_getattr, int, dfd, const char __user *, filename,
struct filename *name __free(putname) = NULL;
unsigned int lookup_flags = 0;
struct file_attr fattr;
- struct file_kattr fa;

+ struct file_kattr fa = {};

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+7c3175...@syzkaller.appspotmail.com
Tested-by: syzbot+7c3175...@syzkaller.appspotmail.com

Tested on:

commit: b7ff7151 Merge tag 'hwmon-for-v6.19-final' of git://gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=145e878a580000

kernel config: https://syzkaller.appspot.com/x/.config?x=9682a42d8ec8b05c
dashboard link: https://syzkaller.appspot.com/bug?extid=7c31755f2cea07838b0c
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=10bc27fa580000

[Edward Adam Davis]

syzbot reported a uninit-value bug in [1].

Similar to the "*get" context where the kernel's internal file_kattr
structure is initialized before calling vfs_fileattr_get(), we should
use the same mechanism when using fa.

[1]

BUG: KMSAN: uninit-value in fuse_fileattr_get+0xeb4/0x1450 fs/fuse/ioctl.c:517
fuse_fileattr_get+0xeb4/0x1450 fs/fuse/ioctl.c:517
vfs_fileattr_get fs/file_attr.c:94 [inline]
__do_sys_file_getattr fs/file_attr.c:416 [inline]

Local variable fa.i created at:
__do_sys_file_getattr fs/file_attr.c:380 [inline]
__se_sys_file_getattr+0x8c/0xbd0 fs/file_attr.c:372

Reported-by: syzbot+7c3175...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=7c31755f2cea07838b0c
Tested-by: syzbot+7c3175...@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---
fs/file_attr.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/file_attr.c b/fs/file_attr.c
index 13cdb31a3e94..4889cf59b256 100644

--- a/fs/file_attr.c
+++ b/fs/file_attr.c
@@ -377,7 +377,7 @@ SYSCALL_DEFINE5(file_getattr, int, dfd, const char __user *, filename,
struct filename *name __free(putname) = NULL;
unsigned int lookup_flags = 0;
struct file_attr fattr;
- struct file_kattr fa;

+ struct file_kattr fa = { .flags_valid = true }; /* hint only */

int error;

BUILD_BUG_ON(sizeof(struct file_attr) < FILE_ATTR_SIZE_VER0);

--
2.43.0

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+7c3175...@syzkaller.appspotmail.com
Tested-by: syzbot+7c3175...@syzkaller.appspotmail.com

Tested on:

commit: b7ff7151 Merge tag 'hwmon-for-v6.19-final' of git://gi..
git tree: upstream

console output: https://syzkaller.appspot.com/x/log.txt?x=16fe878a580000

kernel config: https://syzkaller.appspot.com/x/.config?x=9682a42d8ec8b05c
dashboard link: https://syzkaller.appspot.com/bug?extid=7c31755f2cea07838b0c
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=14978a52580000