[8/9] NFS: When mounting, don't share filesystems between different user namespaces

Commit Message

Trond Myklebust April 24, 2019, 9:46 p.m. UTC

If two different containers that share the same network namespace attempt
to mount the same filesystem, we should not allow them to share the same
super block if they do not share the same user namespace, since the
user mappings on the wire will need to differ.

Signed-off-by: Trond Myklebust <[e-mail]>
---
 fs/nfs/super.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

Patch

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index c27ac96a95bd..1730abc1e9ed 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -2476,6 +2476,21 @@  static int nfs_compare_super_address(struct nfs_server *server1,
 	return 1;
 }
 
+static int nfs_compare_userns(const struct nfs_server *old,
+		const struct nfs_server *new)
+{
+	const struct user_namespace *oldns = &init_user_ns;
+	const struct user_namespace *newns = &init_user_ns;
+
+	if (old->client && old->client->cl_cred)
+		oldns = old->client->cl_cred->user_ns;
+	if (new->client && new->client->cl_cred)
+		newns = new->client->cl_cred->user_ns;
+	if (oldns != newns)
+		return 0;
+	return 1;
+}
+
 static int nfs_compare_super(struct super_block *sb, void *data)
 {
 	struct nfs_sb_mountdata *sb_mntdata = data;
@@ -2489,6 +2504,8 @@  static int nfs_compare_super(struct super_block *sb, void *data)
 		return 0;
 	if (memcmp(&old->fsid, &server->fsid, sizeof(old->fsid)) != 0)
 		return 0;
+	if (!nfs_compare_userns(old, server))
+		return 0;
 	return nfs_compare_mount_options(sb, server, mntflags);
 }