rxrpc: Allow CHALLENGEs to the passed to the app for a RESPONSE

Allow the app to request that CHALLENGEs be passed to it through an
out-of-band queue that allows recvmsg() to pick it up so that the app can
add data to it with sendmsg().

This will allow the application (AFS or userspace) to interact with the
process if it wants to and put values into user-defined fields.  This will
be used by AFS when talking to a fileserver to supply that fileserver with
a crypto key by which callback RPCs can be encrypted (ie. notifications
from the fileserver to the client).

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
Link: https://patch.msgid.link/20250411095303.2316168-5-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 102 insertions, 18 deletions

diff --git a/net/rxrpc/recvmsg.c b/net/rxrpc/recvmsg.c
index 4c622752a569..86a27fb55a1c 100644
--- a/net/rxrpc/recvmsg.c
+++ b/net/rxrpc/recvmsg.c
@@ -155,6 +155,82 @@ static int rxrpc_verify_data(struct rxrpc_call *call, struct sk_buff *skb)
 }
 
 /*
+ * Transcribe a call's user ID to a control message.
+ */
+static int rxrpc_recvmsg_user_id(struct rxrpc_call *call, struct msghdr *msg,
+				 int flags)
+{
+	if (!test_bit(RXRPC_CALL_HAS_USERID, &call->flags))
+		return 0;
+
+	if (flags & MSG_CMSG_COMPAT) {
+		unsigned int id32 = call->user_call_ID;
+
+		return put_cmsg(msg, SOL_RXRPC, RXRPC_USER_CALL_ID,
+				sizeof(unsigned int), &id32);
+	} else {
+		unsigned long idl = call->user_call_ID;
+
+		return put_cmsg(msg, SOL_RXRPC, RXRPC_USER_CALL_ID,
+				sizeof(unsigned long), &idl);
+	}
+}
+
+/*
+ * Deal with a CHALLENGE packet.
+ */
+static int rxrpc_recvmsg_challenge(struct socket *sock, struct msghdr *msg,
+				   struct sk_buff *challenge, unsigned int flags)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(challenge);
+	struct rxrpc_connection *conn = sp->chall.conn;
+
+	return conn->security->challenge_to_recvmsg(conn, challenge, msg);
+}
+
+/*
+ * Process OOB packets.  Called with the socket locked.
+ */
+static int rxrpc_recvmsg_oob(struct socket *sock, struct msghdr *msg,
+			     unsigned int flags)
+{
+	struct rxrpc_sock *rx = rxrpc_sk(sock->sk);
+	struct sk_buff *skb;
+	bool need_response = false;
+	int ret;
+
+	skb = skb_peek(&rx->recvmsg_oobq);
+	if (!skb)
+		return -EAGAIN;
+	rxrpc_see_skb(skb, rxrpc_skb_see_recvmsg);
+
+	ret = put_cmsg(msg, SOL_RXRPC, RXRPC_OOB_ID, sizeof(u64),
+		       &skb->skb_mstamp_ns);
+	if (ret < 0)
+		return ret;
+
+	switch ((enum rxrpc_oob_type)skb->mark) {
+	case RXRPC_OOB_CHALLENGE:
+		need_response = true;
+		ret = rxrpc_recvmsg_challenge(sock, msg, skb, flags);
+		break;
+	default:
+		WARN_ONCE(1, "recvmsg() can't process unknown OOB type %u\n",
+			  skb->mark);
+		ret = -EIO;
+		break;
+	}
+
+	if (!(flags & MSG_PEEK))
+		skb_unlink(skb, &rx->recvmsg_oobq);
+	if (need_response)
+		rxrpc_add_pending_oob(rx, skb);
+	else
+		rxrpc_free_skb(skb, rxrpc_skb_put_oob);
+	return ret;
+}
+
+/*
  * Deliver messages to a call.  This keeps processing packets until the buffer
  * is filled and we find either more DATA (returns 0) or the end of the DATA
  * (returns 1).  If more packets are required, it returns -EAGAIN and if the
@@ -165,6 +241,7 @@ static int rxrpc_recvmsg_data(struct socket *sock, struct rxrpc_call *call,
 			      size_t len, int flags, size_t *_offset)
 {
 	struct rxrpc_skb_priv *sp;
+	struct rxrpc_sock *rx = rxrpc_sk(sock->sk);
 	struct sk_buff *skb;
 	rxrpc_seq_t seq = 0;
 	size_t remain;
@@ -207,7 +284,6 @@ static int rxrpc_recvmsg_data(struct socket *sock, struct rxrpc_call *call,
 			trace_rxrpc_recvdata(call, rxrpc_recvmsg_next, seq,
 					     sp->offset, sp->len, ret2);
 			if (ret2 < 0) {
-				kdebug("verify = %d", ret2);
 				ret = ret2;
 				goto out;
 			}
@@ -255,6 +331,13 @@ static int rxrpc_recvmsg_data(struct socket *sock, struct rxrpc_call *call,
 
 		if (!(flags & MSG_PEEK))
 			rxrpc_rotate_rx_window(call);
+
+		if (!rx->app_ops &&
+		    !skb_queue_empty_lockless(&rx->recvmsg_oobq)) {
+			trace_rxrpc_recvdata(call, rxrpc_recvmsg_oobq, seq,
+					     rx_pkt_offset, rx_pkt_len, ret);
+			break;
+		}
 	}
 
 out:
@@ -262,6 +345,7 @@ out:
 		call->rx_pkt_offset = rx_pkt_offset;
 		call->rx_pkt_len = rx_pkt_len;
 	}
+
 done:
 	trace_rxrpc_recvdata(call, rxrpc_recvmsg_data_return, seq,
 			     rx_pkt_offset, rx_pkt_len, ret);
@@ -301,6 +385,7 @@ try_again:
 	/* Return immediately if a client socket has no outstanding calls */
 	if (RB_EMPTY_ROOT(&rx->calls) &&
 	    list_empty(&rx->recvmsg_q) &&
+	    skb_queue_empty_lockless(&rx->recvmsg_oobq) &&
 	    rx->sk.sk_state != RXRPC_SERVER_LISTENING) {
 		release_sock(&rx->sk);
 		return -EAGAIN;
@@ -322,7 +407,8 @@ try_again:
 		if (ret)
 			goto wait_error;
 
-		if (list_empty(&rx->recvmsg_q)) {
+		if (list_empty(&rx->recvmsg_q) &&
+		    skb_queue_empty_lockless(&rx->recvmsg_oobq)) {
 			if (signal_pending(current))
 				goto wait_interrupted;
 			trace_rxrpc_recvmsg(0, rxrpc_recvmsg_wait, 0);
@@ -332,6 +418,15 @@ try_again:
 		goto try_again;
 	}
 
+	/* Deal with OOB messages before we consider getting normal data. */
+	if (!skb_queue_empty_lockless(&rx->recvmsg_oobq)) {
+		ret = rxrpc_recvmsg_oob(sock, msg, flags);
+		release_sock(&rx->sk);
+		if (ret == -EAGAIN)
+			goto try_again;
+		goto error_no_call;
+	}
+
 	/* Find the next call and dequeue it if we're not just peeking.  If we
 	 * do dequeue it, that comes with a ref that we will need to release.
 	 * We also want to weed out calls that got requeued whilst we were
@@ -342,7 +437,8 @@ try_again:
 	call = list_entry(l, struct rxrpc_call, recvmsg_link);
 
 	if (!rxrpc_call_is_complete(call) &&
-	    skb_queue_empty(&call->recvmsg_queue)) {
+	    skb_queue_empty(&call->recvmsg_queue) &&
+	    skb_queue_empty(&rx->recvmsg_oobq)) {
 		list_del_init(&call->recvmsg_link);
 		spin_unlock_irq(&rx->recvmsg_lock);
 		release_sock(&rx->sk);
@@ -377,21 +473,9 @@ try_again:
 	if (test_bit(RXRPC_CALL_RELEASED, &call->flags))
 		BUG();
 
-	if (test_bit(RXRPC_CALL_HAS_USERID, &call->flags)) {
-		if (flags & MSG_CMSG_COMPAT) {
-			unsigned int id32 = call->user_call_ID;
-
-			ret = put_cmsg(msg, SOL_RXRPC, RXRPC_USER_CALL_ID,
-				       sizeof(unsigned int), &id32);
-		} else {
-			unsigned long idl = call->user_call_ID;
-
-			ret = put_cmsg(msg, SOL_RXRPC, RXRPC_USER_CALL_ID,
-				       sizeof(unsigned long), &idl);
-		}
-		if (ret < 0)
-			goto error_unlock_call;
-	}
+	ret = rxrpc_recvmsg_user_id(call, msg, flags);
+	if (ret < 0)
+		goto error_unlock_call;
 
 	if (msg->msg_name && call->peer) {
 		size_t len = sizeof(call->dest_srx);