rxrpc: Fix conn-level packet handling to unshare RESPONSE packets

The security operations that verify the RESPONSE packets decrypt bits of it
in place - however, the sk_buff may be shared with a packet sniffer, which
would lead to the sniffer seeing an apparently corrupt packet (actually
decrypted).

Fix this by handing a copy of the packet off to the specific security
handler if the packet was cloned.

Fixes: 17926a79320a ("[AF_RXRPC]: Provide secure RxRPC sockets for use by userspace and kernel both")
Closes: https://sashiko.dev/#/patchset/20260408121252.2249051-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jeffrey Altman <jaltman@auristor.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: stable@kernel.org
Link: https://patch.msgid.link/20260422161438.2593376-5-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/rxrpc/conn_event.c b/net/rxrpc/conn_event.c
index 9a41ec708aeb9f5ee0c4edc1548e54d54bf7d9df..aee977291d90bd977a22c957f98897ef7c26e789 100644 (file)
--- a/net/rxrpc/conn_event.c
+++ b/net/rxrpc/conn_event.c
@@ -240,6 +240,33 @@ static void rxrpc_call_is_secure(struct rxrpc_call *call)
                rxrpc_notify_socket(call);
 }
 
+static int rxrpc_verify_response(struct rxrpc_connection *conn,
+                                struct sk_buff *skb)
+{
+       int ret;
+
+       if (skb_cloned(skb)) {
+               /* Copy the packet if shared so that we can do in-place
+                * decryption.
+                */
+               struct sk_buff *nskb = skb_copy(skb, GFP_NOFS);
+
+               if (nskb) {
+                       rxrpc_new_skb(nskb, rxrpc_skb_new_unshared);
+                       ret = conn->security->verify_response(conn, nskb);
+                       rxrpc_free_skb(nskb, rxrpc_skb_put_response_copy);
+               } else {
+                       /* OOM - Drop the packet. */
+                       rxrpc_see_skb(skb, rxrpc_skb_see_unshare_nomem);
+                       ret = -ENOMEM;
+               }
+       } else {
+               ret = conn->security->verify_response(conn, skb);
+       }
+
+       return ret;
+}
+
 /*
  * connection-level Rx packet processor
  */
@@ -270,7 +297,7 @@ static int rxrpc_process_event(struct rxrpc_connection *conn,
                }
                spin_unlock_irq(&conn->state_lock);
 
-               ret = conn->security->verify_response(conn, skb);
+               ret = rxrpc_verify_response(conn, skb);
                if (ret < 0)
                        return ret;