FAILED: patch "[PATCH] NFS: reject request for id_legacy key without auxdata" failed to apply to 3.18-stable tree

The patch below does not apply to the 3.18-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Eric Biggers <[email protected]>
Date: Fri, 19 Jan 2018 15:15:34 -0800
Subject: [PATCH] NFS: reject request for id_legacy key without auxdata

nfs_idmap_legacy_upcall() is supposed to be called with 'aux' pointing to a 'struct idmap', via the call to request_key_with_auxdata() in nfs_idmap_request_key().

However it can also be reached via the request_key() system call in which case 'aux' will be NULL, causing a NULL pointer dereference in nfs_idmap_prepare_pipe_upcall(), assuming that the key description is valid enough to get that far.

Fix this by making nfs_idmap_legacy_upcall() negate the key if no auxdata is provided.

As usual, this bug was found by syzkaller. A simple reproducer using the command-line keyctl program is:

keyctl request2 id_legacy uid:0 '' @s

index 30426c1a1bbd..22dc30a679a0 100644
@@ -568,9 +568,13 @@ static int nfs_idmap_legacy_upcall(struct key_construction *cons,
 	struct idmap_msg *im;
 	struct idmap *idmap = (struct idmap *)aux;
 	struct key *key = cons->key;
-	int ret = -ENOMEM;
+	int ret = -ENOKEY;
+
+	if (!aux)
+		goto out1;
 
 	/* msg and im are freed in idmap_pipe_destroy_msg */
+	ret = -ENOMEM;
 	data = kzalloc(sizeof(*data), GFP_KERNEL);
 	if (!data)
 		goto out1;