linux-kernel - [PATCH] fs: Prevent non-symlinks from entering pick link

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Message-ID: <tencent_7FB38DB725848DA99213DDB35DBF195FCF07@qq.com>
Date: Wed, 18 Jun 2025 11:30:48 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+1aa90f0eb1fc3e77d969@...kaller.appspotmail.com
Cc: almaz.alexandrovich@...agon-software.com,
	brauner@...nel.org,
	jack@...e.cz,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	ntfs3@...ts.linux.dev,
	syzkaller-bugs@...glegroups.com,
	viro@...iv.linux.org.uk
Subject: [PATCH] fs: Prevent non-symlinks from entering pick link

The reproducer uses a file0 on a ntfs3 file system with a corrupted i_link.
When renaming, the file0's inode is marked as a bad inode because the file
name cannot be deleted. However, before renaming, file0 is a directory.
After the renaming fails, it is marked as a bad inode, which makes it a
regular file. In any case, when opening it after creating a hard link,
pick_link() should not be entered because it is not a symbolic link from
beginning to end.

Add a check on the symbolic link before entering pick_link() to avoid
triggering unknown exceptions when performing the i_link acquisition
operation on other types of files.

Reported-by: syzbot+1aa90f0eb1fc3e77d969@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=1aa90f0eb1fc3e77d969
Tested-by: syzbot+1aa90f0eb1fc3e77d969@...kaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@...com>
---
 fs/namei.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index 4bb889fc980b..1524a5359d46 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2005,6 +2005,10 @@ static const char *step_into(struct nameidata *nd, int flags,
 		if (path.mnt == nd->path.mnt)
 			mntget(path.mnt);
 	}
+
+	if (inode && !S_ISLNK(inode->i_mode))
+		return NULL;
+
 	return pick_link(nd, &path, inode, flags);
 }

-- 
2.43.0