Patch "NFS: reject request for id_legacy key without auxdata" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

NFS: reject request for id_legacy key without auxdata

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
nfs-reject-request-for-id_legacy-key-without-auxdata.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

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

From: Eric Biggers <[email protected]>

commit 49686cbbb3ebafe42e63868222f269d8053ead00 upstream.

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

---
 fs/nfs/nfs4idmap.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

@@ -567,9 +567,13 @@ static int nfs_idmap_legacy_upcall(struc
 	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;

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/keys-encrypted-fix-buffer-overread-in-valid_master_desc.patch queue-4.4/x86-kaiser-fix-build-error-with-kasan-function_graph_tracer.patch queue-4.4/nfs-reject-request-for-id_legacy-key-without-auxdata.patch