[PATCH v3 35/38] overlayfs: do not mount on top of idmapped mounts

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@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <redacted>
---
/* v2 */
patch introduced

/* v3 */
- Amir Goldstein [off-list ref]:
  - Move check for idmapped lower layers into ovl_mount_dir_noesc().
- David Howells [off-list ref]:
  - Adapt check after removing mnt_idmapped() helper.
---
 fs/overlayfs/super.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 0d4f2baf6836..5002f97b01e6 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;

-- 
2.29.2