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>

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index edbb3eb..5f0d199 100644 (file)
--- 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;