Forwarded: [PATCH] ntfs3: prevent MFT inode resize operations

syzbot
2025-10-14T07:38:45Z

Subject: [PATCH] ntfs3: prevent MFT inode resize operations
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

The MFT (Master File Table) inode does not have its run_lock rwsem
initialized, as noted in ntfs_file_release(). When a truncate operation
is attempted on the MFT inode, ntfs_truncate() tries to acquire the
uninitialized run_lock, triggering a lockdep warning about using a
non-static key.

The MFT is a special system file that should not be resized by user
operations. Add a check in ntfs_setattr() to reject any size change
attempts on the MFT inode with -EPERM before reaching ntfs_truncate().

This is consistent with the existing design where ntfs_file_release()
explicitly skips operations on MFT due to the missing run_lock
initialization.

Reported-by: syzbot+3e58a7dc1a8c00243999@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3e58a7dc1a8c00243999
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
fs/ntfs3/file.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/ntfs3/file.c b/fs/ntfs3/file.c
index 4c90ec2fa2ea..2555850483c4 100644
--- a/fs/ntfs3/file.c
+++ b/fs/ntfs3/file.c
@@ -792,7 +792,13 @@ int ntfs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,

if (ia_valid & ATTR_SIZE) {
loff_t newsize, oldsize;
-
+ ntfs_warn(inode->i_sb,
+ "DEBUG: Truncating inode %lu (MFT_REC_MFT is %d)",
+ inode->i_ino, MFT_REC_MFT);
+ if (inode->i_ino == MFT_REC_MFT) {
+ err = -EPERM;
+ goto out;
+ }
if (WARN_ON(ni->ni_flags & NI_FLAG_COMPRESSED_MASK)) {
/* Should never be here, see ntfs_file_open(). */
err = -EOPNOTSUPP;
--
2.34.1