FAILED: patch "[PATCH] ovl: force r/o mount when index dir creation fails" failed to apply to 4.14-stable tree

The patch below does not apply to the 4.14-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Amir Goldstein <[email protected]>
Date: Tue, 19 Sep 2017 12:14:18 +0300
Subject: [PATCH] ovl: force r/o mount when index dir creation fails

When work dir creation fails, a warning is emitted and overlay is mounted r/o. Trying to remount r/w will fail with no work dir.

When index dir creation fails, the same warning is emitted and overlay is mounted r/o, but trying to remount r/w will succeed. This may cause unintentional corruption of filesystem consistency.

Adjust the behavior of index dir creation failure to that of work dir creation failure and do not allow to remount r/w. User needs to state an explicitly intention to work without an index by mounting with option 'index=off' to allow r/w mount with no index dir.

When mounting with option 'index=on' and no 'upperdir', index is implicitly disabled, so do not warn about no file handle support.

The issue was introduced with inodes index feature in v4.13, but this patch will not apply cleanly before ovl_fill_super() re-factoring in v4.15.

index f3281f0b2388..9aa5d32af427 100644
@@ -699,7 +699,8 @@ static int ovl_lower_dir(const char *name, struct path *path,
 	 * The inodes index feature needs to encode and decode file
 	 * handles, so it requires that all layers support them.
 	 */
-	if (ofs->config.index && !ovl_can_decode_fh(path->dentry->d_sb)) {
+	if (ofs->config.index && ofs->config.upperdir &&
+	    !ovl_can_decode_fh(path->dentry->d_sb)) {
 		ofs->config.index = false;
 		pr_warn("overlayfs: fs on '%s' does not support file handles, falling back to index=off.\n", name);
 	}

@@ -1268,11 +1269,16 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 		if (err)
 			goto out_free_oe;
 
-		if (!ofs->indexdir)
+		/* Force r/o mount with no index dir */
+		if (!ofs->indexdir) {
+			dput(ofs->workdir);
+			ofs->workdir = NULL;
 			sb->s_flags |= SB_RDONLY;
+		}
+
 	}
 
-	/* Show index=off/on in /proc/mounts for any of the reasons above */
+	/* Show index=off in /proc/mounts for forced r/o mount */
 	if (!ofs->indexdir)
 		ofs->config.index = false;