Re: [PATCH V3] fs/ntfs3: check if the inode is bad before creating symlink

[Lizhi Xu]

On Thu, 21 Nov 2024 03:55:29 +0000, Al Viro wrote:
> >   user_path_at()->
> >     filename_lookup()->
> >       path_lookupat()->
> >         lookup_last()->
> >           walk_component()->
> >             __lookup_slow()->
> >               ntfs_lookup()->
> >                 d_splice_alias()->
> >
> > 2. The subsequent chmod fails, causing the inode to be set to bad.
> 
> What's wrong with "return an error"?
make_bad_inode() is executed in attr_set_size() and the error code -ENOENT is returned;
attr_set_size() defined in fs/ntfs3/attrib.c
> 
> > 3. During the link operation, d_instantiate() is executed in ntfs_link() to associate the bad inode with the dentry.
> 
> Yecchhh...  If nothing else, check for is_bad_inode() should be there
> for as long as make_bad_inode() is done on live inodes.
I checked is_bad_inode() in ntfs_link(), see line 146 of ntfs_link(), please see my V3 of the patch [2].

[1]
fs/ntfs3/namei.c
 19 static int ntfs_link(struct dentry *ode, struct inode *dir, struct dentry *de)
 18 {
 17         int err;
 16         struct inode *inode = d_inode(ode);
 15         struct ntfs_inode *ni = ntfs_i(inode);
 14
 13         if (S_ISDIR(inode->i_mode))
 12                 return -EPERM;
 11
 10         if (inode->i_nlink >= NTFS_LINK_MAX)
  9                 return -EMLINK;
  8
  7         ni_lock_dir(ntfs_i(dir));
  6         if (inode != dir)
  5                 ni_lock(ni);
  4
  3         inc_nlink(inode);
  2         ihold(inode);
  1
146         err = ntfs_link_inode(inode, de);
  1
  2         if (!err) {
  3                 inode_set_ctime_current(inode);
  4                 inode_set_mtime_to_ts(dir, inode_set_ctime_current(dir));
  5                 mark_inode_dirty(inode);
  6                 mark_inode_dirty(dir);
  7                 d_instantiate(de, inode);

[2]  
Reported-by: syzbot+73d8fc29ec7cba8286fa@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=73d8fc29ec7cba8286fa
Signed-off-by: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx>
---
V1 --> V2: add the root cause of the i_link not set issue and imporve the check
V2 --> V3: when creating a symbolic link, first check whether the inode of file is bad.

 fs/ntfs3/inode.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ntfs3/inode.c b/fs/ntfs3/inode.c
index be04d2845bb7..fefbdcf75016 100644
--- a/fs/ntfs3/inode.c
+++ b/fs/ntfs3/inode.c
@@ -1719,6 +1719,9 @@ int ntfs_link_inode(struct inode *inode, struct dentry *dentry)
 	struct ntfs_sb_info *sbi = inode->i_sb->s_fs_info;
 	struct NTFS_DE *de;

+	if (is_bad_inode(inode))
+		return -EIO;
+
 	/* Allocate PATH_MAX bytes. */
 	de = __getname();
 	if (!de)