[PATCH net 1/5] rxrpc: rxrpc_verify_data ensure rx_dec_buffer alloc

[David Howells <dhowells@redhat.com>]

From: Jeffrey Altman <jaltman@auristor.com>

rxrpc_recvmsg_data() calls rxrpc_verify_data() whenever the
rxrpc_call.rx_dec_buffer is unallocated and assumes that upon
successful return that rx_dec_buffer must be allocated.
However, rxrpc_verify_data() does not request an allocation if
the rxrpc_skb_priv.len is zero.

In addition, failure to allocate rx_dec_buffer will result in a
call to skb_copy_bits() with a NULL destination which can
trigger a NULL pointer dereference.

To prevent these issues rxrpc_verify_data() is modified to
always attempt to allocate the rxrpc_call.rx_dec_buffer if it
is NULL.

This issue was identified with assistance of a private
sashiko instance.

Fixes: d2bc90cf6c75cb ("rxrpc: Fix DATA decrypt vs splice() by copying data to buffer in recvmsg")
Reported-by: Simon Horman <simon.horman@redhat.com>
Signed-off-by: Jeffrey Altman <jaltman@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jiayuan Chen <jiayuan.chen@linux.dev>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Eric Dumazet <edumazet@google.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: netdev@vger.kernel.org
cc: stable@kernel.org
---
 net/rxrpc/recvmsg.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/rxrpc/recvmsg.c b/net/rxrpc/recvmsg.c
index c940600117a4..a3cf5358f16e 100644
--- a/net/rxrpc/recvmsg.c
+++ b/net/rxrpc/recvmsg.c
@@ -161,7 +161,7 @@ static int rxrpc_verify_data(struct rxrpc_call *call, struct sk_buff *skb)
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
 	int ret;
 
-	if (sp->len > call->rx_dec_bsize) {
+	if (sp->len > call->rx_dec_bsize || !call->rx_dec_buffer) {
 		/* Make sure we can hold a 1412-byte jumbo subpacket and make
 		 * sure that the buffer size is aligned to a crypto blocksize.
 		 */