[PATCH v4 37/40] overlayfs: do not mount on top of idmapped mounts

Christian Brauner christian.brauner at ubuntu.com
Thu Dec 3 23:57:33 UTC 2020

Prevent overlayfs from being mounted on top of idmapped mounts until we
have ported it to handle this case and added proper testing for it.

Cc: Christoph Hellwig <hch at lst.de>
Cc: David Howells <dhowells at redhat.com>
Cc: Al Viro <viro at zeniv.linux.org.uk>
Cc: linux-fsdevel at vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner at ubuntu.com>
/* v2 */
patch introduced

/* v3 */
- Amir Goldstein <amir73il at gmail.com>:
  - Move check for idmapped lower layers into ovl_mount_dir_noesc().
- David Howells <dhowells at redhat.com>:
  - Adapt check after removing mnt_idmapped() helper.

/* v4 */
 fs/overlayfs/super.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index aed21e569390..2be17c769322 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -811,6 +811,10 @@ static int ovl_mount_dir_noesc(const char *name, struct path *path)
 		pr_err("filesystem on '%s' not supported\n", name);
 		goto out_put;
+	if (mnt_user_ns(path->mnt) != &init_user_ns) {
+		pr_err("idmapped layers are currently not supported\n");
+		goto out_put;
+	}
 	if (!d_is_dir(path->dentry)) {
 		pr_err("'%s' not a directory\n", name);
 		goto out_put;

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