ovl: verify upper dentry in ovl_remove_and_whiteout()

The upper dentry may become stale before we call ovl_lock_rename_workdir.
For example, someone could (mistakenly or maliciously) manually unlink(2)
it directly from upperdir.

To ensure it is not stale, let's lookup it after ovl_lock_rename_workdir
and and check if it matches the upper dentry.

Essentially, it is the same problem and similar solution as in
commit 11f3710417d0 ("ovl: verify upper dentry before unlink and rename").

Signed-off-by: Maxim Patlasov <mpatlasov@virtuozzo.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org>

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index c2a6b08..5c9d2d8 100644 (file)
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -505,6 +505,7 @@ static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir)
        struct dentry *upper;
        struct dentry *opaquedir = NULL;
        int err;
+       int flags = 0;
 
        if (WARN_ON(!workdir))
                return -EROFS;
@@ -534,46 +535,39 @@ static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir)
        if (err)
                goto out_dput;
 
-       whiteout = ovl_whiteout(workdir, dentry);
-       err = PTR_ERR(whiteout);
-       if (IS_ERR(whiteout))
+       upper = lookup_one_len(dentry->d_name.name, upperdir,
+                              dentry->d_name.len);
+       err = PTR_ERR(upper);
+       if (IS_ERR(upper))
                goto out_unlock;
 
-       upper = ovl_dentry_upper(dentry);
-       if (!upper) {
-               upper = lookup_one_len(dentry->d_name.name, upperdir,
-                                      dentry->d_name.len);
-               err = PTR_ERR(upper);
-               if (IS_ERR(upper))
-                       goto kill_whiteout;
-
-               err = ovl_do_rename(wdir, whiteout, udir, upper, 0);
-               dput(upper);
-               if (err)
-                       goto kill_whiteout;
-       } else {
-               int flags = 0;
+       err = -ESTALE;
+       if ((opaquedir && upper != opaquedir) ||
+           (!opaquedir && ovl_dentry_upper(dentry) &&
+            upper != ovl_dentry_upper(dentry))) {
+               goto out_dput_upper;
+       }
 
-               if (opaquedir)
-                       upper = opaquedir;
-               err = -ESTALE;
-               if (upper->d_parent != upperdir)
-                       goto kill_whiteout;
+       whiteout = ovl_whiteout(workdir, dentry);
+       err = PTR_ERR(whiteout);
+       if (IS_ERR(whiteout))
+               goto out_dput_upper;
 
-               if (is_dir)
-                       flags |= RENAME_EXCHANGE;
+       if (d_is_dir(upper))
+               flags = RENAME_EXCHANGE;
 
-               err = ovl_do_rename(wdir, whiteout, udir, upper, flags);
-               if (err)
-                       goto kill_whiteout;
+       err = ovl_do_rename(wdir, whiteout, udir, upper, flags);
+       if (err)
+               goto kill_whiteout;
+       if (flags)
+               ovl_cleanup(wdir, upper);
 
-               if (is_dir)
-                       ovl_cleanup(wdir, upper);
-       }
        ovl_dentry_version_inc(dentry->d_parent);
 out_d_drop:
        d_drop(dentry);
        dput(whiteout);
+out_dput_upper:
+       dput(upper);
 out_unlock:
        unlock_rename(workdir, upperdir);
 out_dput: