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

[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+7c31755f2cea07838b0c@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
=====================================================


---
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If the report is already addressed, let syzbot know by replying with:
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If you want syzbot to run the reproducer, reply with:
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If the report is a duplicate of another one, reply with:
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#syz undup

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

[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;

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

[syzbot]

Hello,

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

Reported-by: syzbot+7c31755f2cea07838b0c@syzkaller.appspotmail.com
Tested-by: syzbot+7c31755f2cea07838b0c@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.

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

[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);

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

[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 = {};
 	int error;
 
 	BUILD_BUG_ON(sizeof(struct file_attr) < FILE_ATTR_SIZE_VER0);

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

[syzbot]

Hello,

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

Reported-by: syzbot+7c31755f2cea07838b0c@syzkaller.appspotmail.com
Tested-by: syzbot+7c31755f2cea07838b0c@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

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

[PATCH] fs: init flags_valid before calling vfs_fileattr_get

[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+7c31755f2cea07838b0c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=7c31755f2cea07838b0c
Tested-by: syzbot+7c31755f2cea07838b0c@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@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

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

[syzbot]

Hello,

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

Reported-by: syzbot+7c31755f2cea07838b0c@syzkaller.appspotmail.com
Tested-by: syzbot+7c31755f2cea07838b0c@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

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