ovl: fix permission checking for setattr

szmi · Al Viro · commit acff81ec2c79 · 2015-12-06T12:28:23.000-05:00
[Al Viro] The bug is in being too enthusiastic about optimizing -&gt;setattr()
away - instead of "copy verbatim with metadata" + "chmod/chown/utimes"
(with the former being always safe and the latter failing in case of
insufficient permissions) it tries to combine these two.  Note that copyup
itself will have to do -&gt;setattr() anyway; _that_ is where the elevated
capabilities are right.  Having these two -&gt;setattr() (one to set verbatim
copy of metadata, another to do what overlayfs -&gt;setattr() had been asked
to do in the first place) combined is where it breaks.

Signed-off-by: Miklos Szeredi &lt;miklos@szeredi.hu&gt;
Cc: &lt;stable@vger.kernel.org&gt;
Signed-off-by: Al Viro &lt;viro@zeniv.linux.org.uk&gt;
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
@@ -49,13 +49,13 @@ int ovl_setattr(struct dentry *dentry, struct iattr *attr)
 	if (err)
 		goto out;
 
-	upperdentry = ovl_dentry_upper(dentry);
-	if (upperdentry) {
+	err = ovl_copy_up(dentry);
+	if (!err) {
+		upperdentry = ovl_dentry_upper(dentry);
+
 		mutex_lock(&upperdentry->d_inode->i_mutex);
 		err = notify_change(upperdentry, attr, NULL);
 		mutex_unlock(&upperdentry->d_inode->i_mutex);
-	} else {
-		err = ovl_copy_up_last(dentry, attr, false);
 	}
 	ovl_drop_write(dentry);
 out:
