[syzbot] [fs?] KMSAN: uninit-value in full_proxy_unlocked_ioctl

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b4b0881156fb Merge tag 'docs-6.14-2' of git://git.lwn.net/..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=12a04518580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7d0bb5e08cf54aa2
dashboard link: https://syzkaller.appspot.com/bug?extid=8928e473a91452caca2f
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=150776b0580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16aaab64580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4dbe3cd3dcb8/disk-b4b08811.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/592d90859f86/vmlinux-b4b08811.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4cfde2b63c7f/bzImage-b4b08811.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8928e4...@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in full_proxy_unlocked_ioctl+0xed/0x3a0 fs/debugfs/file.c:399
full_proxy_unlocked_ioctl+0xed/0x3a0 fs/debugfs/file.c:399
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:906 [inline]
__se_sys_ioctl+0x246/0x440 fs/ioctl.c:892
__x64_sys_ioctl+0x96/0xe0 fs/ioctl.c:892
x64_sys_call+0x19f0/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
__debugfs_file_get+0xe59/0xef0 fs/debugfs/file.c:120
full_proxy_open_regular+0x67/0xa00 fs/debugfs/file.c:447
do_dentry_open+0x1bdd/0x26b0 fs/open.c:955
vfs_open+0x53/0x5b0 fs/open.c:1085
do_open fs/namei.c:3830 [inline]
path_openat+0x56a1/0x6250 fs/namei.c:3989
do_filp_open+0x268/0x600 fs/namei.c:4016
do_sys_openat2+0x1bf/0x2f0 fs/open.c:1427
do_sys_open fs/open.c:1442 [inline]
__do_sys_openat fs/open.c:1458 [inline]
__se_sys_openat fs/open.c:1453 [inline]
__x64_sys_openat+0x2a1/0x310 fs/open.c:1453
x64_sys_call+0x36f5/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:258
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
__debugfs_file_get+0xdff/0xef0 fs/debugfs/file.c:118
full_proxy_open_regular+0x67/0xa00 fs/debugfs/file.c:447
do_dentry_open+0x1bdd/0x26b0 fs/open.c:955
vfs_open+0x53/0x5b0 fs/open.c:1085
do_open fs/namei.c:3830 [inline]
path_openat+0x56a1/0x6250 fs/namei.c:3989
do_filp_open+0x268/0x600 fs/namei.c:4016
do_sys_openat2+0x1bf/0x2f0 fs/open.c:1427
do_sys_open fs/open.c:1442 [inline]
__do_sys_openat fs/open.c:1458 [inline]
__se_sys_openat fs/open.c:1453 [inline]
__x64_sys_openat+0x2a1/0x310 fs/open.c:1453
x64_sys_call+0x36f5/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:258
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
slab_post_alloc_hook mm/slub.c:4121 [inline]
slab_alloc_node mm/slub.c:4164 [inline]
__kmalloc_cache_noprof+0x8e3/0xdf0 mm/slub.c:4320
kmalloc_noprof include/linux/slab.h:901 [inline]
__debugfs_file_get+0x31d/0xef0 fs/debugfs/file.c:101
full_proxy_open_regular+0x67/0xa00 fs/debugfs/file.c:447
do_dentry_open+0x1bdd/0x26b0 fs/open.c:955
vfs_open+0x53/0x5b0 fs/open.c:1085
do_open fs/namei.c:3830 [inline]
path_openat+0x56a1/0x6250 fs/namei.c:3989
do_filp_open+0x268/0x600 fs/namei.c:4016
do_sys_openat2+0x1bf/0x2f0 fs/open.c:1427
do_sys_open fs/open.c:1442 [inline]
__do_sys_openat fs/open.c:1458 [inline]
__se_sys_openat fs/open.c:1453 [inline]
__x64_sys_openat+0x2a1/0x310 fs/open.c:1453
x64_sys_call+0x36f5/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:258
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 1 UID: 0 PID: 5781 Comm: syz-executor325 Not tainted 6.13.0-syzkaller-09585-gb4b0881156fb #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
=====================================================


---
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[Edward Adam Davis]

#syz test

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index e33cc77699cd..5fbefce2b372 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -102,6 +102,7 @@ static int __debugfs_file_get(struct dentry *dentry, enum dbgfs_get_mode mode)
if (!fsd)
return -ENOMEM;

+ fsd->methods = 0;
if (mode == DBGFS_GET_SHORT) {
const struct debugfs_short_fops *ops;
ops = fsd->short_fops = DEBUGFS_I(inode)->short_fops;

[syzbot]

Hello,

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

Reported-by: syzbot+8928e4...@syzkaller.appspotmail.com
Tested-by: syzbot+8928e4...@syzkaller.appspotmail.com

Tested on:

commit: 2014c95a Linux 6.14-rc1
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16fd2eb0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=aa4f01a8a3baec54

dashboard link: https://syzkaller.appspot.com/bug?extid=8928e473a91452caca2f
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=1710ed18580000

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

[Edward Adam Davis]

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

The newly created fsd does not initialize methods, and increases the
initialization of methods for fsd.

[1]

BUG: KMSAN: uninit-value in full_proxy_unlocked_ioctl+0xed/0x3a0 fs/debugfs/file.c:399
full_proxy_unlocked_ioctl+0xed/0x3a0 fs/debugfs/file.c:399
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:906 [inline]
__se_sys_ioctl+0x246/0x440 fs/ioctl.c:892
__x64_sys_ioctl+0x96/0xe0 fs/ioctl.c:892
x64_sys_call+0x19f0/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Fixes: 41a0ecc0997c ("debugfs: get rid of dynamically allocation proxy_ops")
Reported-by: syzbot+8928e4...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=8928e473a91452caca2f
Tested-by: syzbot+8928e4...@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---
fs/debugfs/file.c | 1 +
1 file changed, 1 insertion(+)

--
2.43.0

[Greg KH]

On Mon, Feb 03, 2025 at 11:27:56AM +0800, Edward Adam Davis wrote:
> syzbot reported a uninit-value in full_proxy_unlocked_ioctl. [1]
>
> The newly created fsd does not initialize methods, and increases the
> initialization of methods for fsd.
>
> [1]
> BUG: KMSAN: uninit-value in full_proxy_unlocked_ioctl+0xed/0x3a0 fs/debugfs/file.c:399
> full_proxy_unlocked_ioctl+0xed/0x3a0 fs/debugfs/file.c:399
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:906 [inline]
> __se_sys_ioctl+0x246/0x440 fs/ioctl.c:892
> __x64_sys_ioctl+0x96/0xe0 fs/ioctl.c:892
> x64_sys_call+0x19f0/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:17
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Fixes: 41a0ecc0997c ("debugfs: get rid of dynamically allocation proxy_ops")
> Reported-by: syzbot+8928e4...@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=8928e473a91452caca2f
> Tested-by: syzbot+8928e4...@syzkaller.appspotmail.com
> Signed-off-by: Edward Adam Davis <ead...@qq.com>
> ---
> fs/debugfs/file.c | 1 +
> 1 file changed, 1 insertion(+)

Is this still an issue on 6.14-rc1, specifically after commit
57b314752ec0 ("debugfs: Fix the missing initializations in
__debugfs_file_get()")?

thanks,

greg k-h

[Edward Adam Davis]

No.

Edward

[Greg KH]

Great, I'll forget about it then :)

thanks!

greg k-h

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.