linux-ext4 - [PATCH v5 39/42] overlayfs: do not mount on top of idmapped mounts

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Date:   Tue, 12 Jan 2021 23:01:21 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel@...r.kernel.org
Cc:     John Johansen <john.johansen@...onical.com>,
        James Morris <jmorris@...ei.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        Geoffrey Thomas <geofft@...reload.com>,
        Mrunal Patel <mpatel@...hat.com>,
        Josh Triplett <josh@...htriplett.org>,
        Andy Lutomirski <luto@...nel.org>,
        Theodore Tso <tytso@....edu>, Alban Crequy <alban@...volk.io>,
        Tycho Andersen <tycho@...ho.ws>,
        David Howells <dhowells@...hat.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Seth Forshee <seth.forshee@...onical.com>,
        Stéphane Graber <stgraber@...ntu.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Aleksa Sarai <cyphar@...har.com>,
        Lennart Poettering <lennart@...ttering.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, smbarber@...omium.org,
        Phil Estes <estesp@...il.com>, Serge Hallyn <serge@...lyn.com>,
        Kees Cook <keescook@...omium.org>,
        Todd Kjos <tkjos@...gle.com>, Paul Moore <paul@...l-moore.com>,
        Jonathan Corbet <corbet@....net>,
        containers@...ts.linux-foundation.org,
        linux-security-module@...r.kernel.org, linux-api@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-integrity@...r.kernel.org, selinux@...r.kernel.org,
        Christian Brauner <christian.brauner@...ntu.com>,
        Christoph Hellwig <hch@....de>
Subject: [PATCH v5 39/42] 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@....de>
Cc: David Howells <dhowells@...hat.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: linux-fsdevel@...r.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
---
/* v2 */
patch introduced

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

/* v4 */
unchanged

/* v5 */
base-commit: 7c53f6b671f4aba70ff15e1b05148b10d58c2837
---
 fs/overlayfs/super.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 24404a167367..c64a6644203e 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -856,6 +856,10 @@ 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;
-- 
2.30.0