1 files changed, 27 insertions, 6 deletions

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index b90952f528b1..5f0d1993e6e3 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -529,8 +529,7 @@ static int ovl_remount(struct super_block *sb, int *flags, char *data)
 {
         struct ovl_fs *ufs = sb->s_fs_info;
 
-        if (!(*flags & MS_RDONLY) &&
-            (!ufs->upper_mnt || (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)))
+        if (!(*flags & MS_RDONLY) && !ufs->upper_mnt)
                 return -EROFS;
 
         return 0;
@@ -615,9 +614,19 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
                         break;
 
                 default:
+                        pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
                         return -EINVAL;
                 }
         }
+
+        /* Workdir is useless in non-upper mount */
+        if (!config->upperdir && config->workdir) {
+                pr_info("overlayfs: option \"workdir=%s\" is useless in a non-upper mount, ignore\n",
+                        config->workdir);
+                kfree(config->workdir);
+                config->workdir = NULL;
+        }
+
         return 0;
 }
 
@@ -837,7 +846,6 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 
         sb->s_stack_depth = 0;
         if (ufs->config.upperdir) {
-                /* FIXME: workdir is not needed for a R/O mount */
                 if (!ufs->config.workdir) {
                         pr_err("overlayfs: missing 'workdir'\n");
                         goto out_free_config;
@@ -847,6 +855,13 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
                 if (err)
                         goto out_free_config;
 
+                /* Upper fs should not be r/o */
+                if (upperpath.mnt->mnt_sb->s_flags & MS_RDONLY) {
+                        pr_err("overlayfs: upper fs is r/o, try multi-lower layers mount\n");
+                        err = -EINVAL;
+                        goto out_put_upperpath;
+                }
+
                 err = ovl_mount_dir(ufs->config.workdir, &workpath);
                 if (err)
                         goto out_put_upperpath;
@@ -869,8 +884,14 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 
         err = -EINVAL;
         stacklen = ovl_split_lowerdirs(lowertmp);
-        if (stacklen > OVL_MAX_STACK)
+        if (stacklen > OVL_MAX_STACK) {
+                pr_err("overlayfs: too many lower directries, limit is %d\n",
+                       OVL_MAX_STACK);
                 goto out_free_lowertmp;
+        } else if (!ufs->config.upperdir && stacklen == 1) {
+                pr_err("overlayfs: at least 2 lowerdir are needed while upperdir nonexistent\n");
+                goto out_free_lowertmp;
+        }
 
         stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
         if (!stack)
@@ -932,8 +953,8 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
                 ufs->numlower++;
         }
 
-        /* If the upper fs is r/o or nonexistent, we mark overlayfs r/o too */
-        if (!ufs->upper_mnt || (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY))
+        /* If the upper fs is nonexistent, we mark overlayfs r/o too */
+        if (!ufs->upper_mnt)
                 sb->s_flags |= MS_RDONLY;
 
         sb->s_d_op = &ovl_dentry_operations;