namei: make permission helpers idmapped mount aware

The two helpers inode_permission() and generic_permission() are used by
the vfs to perform basic permission checking by verifying that the
caller is privileged over an inode. In order to handle idmapped mounts
we extend the two helpers with an additional user namespace argument.
On idmapped mounts the two helpers will make sure to map the inode
according to the mount's user namespace and then peform identical
permission checks to inode_permission() and generic_permission(). If the
initial user namespace is passed nothing changes so non-idmapped mounts
will see identical behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-6-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
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index fc2469a20fed..ff5598cc1de0 100644
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -285,7 +285,7 @@ int kernfs_iop_permission(struct inode *inode, int mask)
 	kernfs_refresh_inode(kn, inode);
 	mutex_unlock(&kernfs_mutex);
 
-	return generic_permission(inode, mask);
+	return generic_permission(&init_user_ns, inode, mask);
 }
 
 int kernfs_xattr_get(struct kernfs_node *kn, const char *name,