ovl: upper fs should not be R/O

After importing multi-lower layer support, users could mount a r/o
partition as the left most lowerdir instead of using it as upperdir.
And a r/o upperdir may cause an error like

	overlayfs: failed to create directory ./workdir/work

during mount.

This patch check the *s_flags* of upper fs and return an error if
it is a r/o partition. The checking of *upper_mnt->mnt_sb->s_flags*
can be removed now.

This patch also remove

	/* FIXME: workdir is not needed for a R/O mount */

from ovl_fill_super() because:

1) for upper fs r/o case
Setting a r/o partition as upper is prevented, no need to care about
workdir in this case.

2) for "mount overlay -o ro" with a r/w upper fs case
Users could remount overlayfs to r/w in this case, so workdir should
not be omitted.

Signed-off-by: hujianyang <hujianyang@huawei.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

1 files changed, 19 insertions, 5 deletions

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index edbb3ebcdaad..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;
@@ -619,6 +618,15 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
                         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;
 }
 
@@ -838,7 +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;
@@ -848,6 +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;
@@ -939,8 +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;