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From:   Christian Brauner <christian.brauner@ubuntu.com>
To:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@lst.de>, linux-fsdevel@vger.kernel.org
Cc:     John Johansen <john.johansen@canonical.com>,
        James Morris <jmorris@namei.org>,
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        containers@lists.linux-foundation.org,
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        Christian Brauner <christian.brauner@ubuntu.com>
Subject: [PATCH v6 28/40] overlayfs: do not mount on top of idmapped mounts
Date:   Thu, 21 Jan 2021 14:19:47 +0100
Message-Id: <20210121131959.646623-29-christian.brauner@ubuntu.com>
In-Reply-To: <20210121131959.646623-1-christian.brauner@ubuntu.com>
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Prevent overlayfs from being mounted on top of idmapped mounts.
Stacking filesystems need to be prevented from being mounted on top of
idmapped mounts until they have have been converted to handle this.

Link: https://lore.kernel.org/r/20210112220124.837960-40-christian.brauner@ubuntu.com
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 <christian.brauner@ubuntu.com>
---
/* v2 */
patch introduced

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

/* v4 */
unchanged

/* v5 */
unchanged
base-commit: 7c53f6b671f4aba70ff15e1b05148b10d58c2837

/* v6 */
unchanged
base-commit: 19c329f6808995b142b3966301f217c831e7cf31
---
 fs/overlayfs/super.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index c04612b19054..b702c576e783 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -858,6 +858,10 @@ 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