[PATCH net v4 2/9] rxrpc: Fix packet encryption error handling

[David Howells <dhowells@redhat.com>]

In rxrpc_send_data(), if ->secure_packet() returns an error, the code
currently just jumps to out: and returns the error to the app on the
assumption that any error returned by this is automatically fatal for the
call, and may even have corrupted the transmission queue - but leaving it
to userspace to deal with.  Nothing stops the application from retrying the
sendmsg(), which will try to encrypt the buffer again, and might succeed
with a corrupt buffer.

Fix rxrpc_send_data() in the following ways:

 (1) If -ENOMEM is returned, assume we never got as far as the encryption
     and that the operation is retryable.  In which case, jump to
     maybe_error_rewind and, if we've copied data into the last packet,
     remove a byte from it so that we don't tell the caller that we've
     completed the transmission phase.

 (2) If any other error occurs, set the TX_ERROR flag on the call and
     return that error directly; on all subsequent attempts to add data to
     the call, return -EIO.  The app must then abort the call to get rid of
     it (this allows the app to choose the abort code to use).

Fixes: 17926a79320a ("[AF_RXRPC]: Provide secure RxRPC sockets for use by userspace and kernel both")
Closes: https://sashiko.dev/#/patchset/20260702144919.172295-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
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: stable@kernel.org
---
 include/trace/events/rxrpc.h |  1 +
 net/rxrpc/ar-internal.h      |  1 +
 net/rxrpc/sendmsg.c          | 39 +++++++++++++++++++++++++++++++-----
 3 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index 704a10de6670..8f3e3967885a 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -148,6 +148,7 @@
 	EM(rxrpc_eproto_wrong_security,		"wrong-sec")		\
 	EM(rxrpc_recvmsg_excess_data,		"recvmsg-excess")	\
 	EM(rxrpc_recvmsg_short_data,		"recvmsg-short")	\
+	EM(rxrpc_sendmsg_tx_error,		"tx-error")		\
 	E_(rxrpc_sendmsg_late_send,		"sendmsg-late")
 
 #define rxrpc_call_poke_traces \
diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 865f05fe37ab..a6f830c1621f 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -642,6 +642,7 @@ enum rxrpc_call_flag {
 	RXRPC_CALL_TX_LAST,		/* Last packet in Tx buffer (at rxtx_top) */
 	RXRPC_CALL_TX_ALL_ACKED,	/* Last packet has been hard-acked */
 	RXRPC_CALL_TX_NO_MORE,		/* No more data to transmit (MSG_MORE deasserted) */
+	RXRPC_CALL_TX_ERROR,		/* Terminal error; call needs abort */
 	RXRPC_CALL_SEND_PING,		/* A ping will need to be sent */
 	RXRPC_CALL_RETRANS_TIMEOUT,	/* Retransmission due to timeout occurred */
 	RXRPC_CALL_BEGAN_RX_TIMER,	/* We began the expect_rx_by timer */
diff --git a/net/rxrpc/sendmsg.c b/net/rxrpc/sendmsg.c
index 4c754f78ece9..d117a25b031d 100644
--- a/net/rxrpc/sendmsg.c
+++ b/net/rxrpc/sendmsg.c
@@ -330,12 +330,18 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
 	bool more = msg->msg_flags & MSG_MORE;
 	int ret, copied = 0;
 
-	if (test_bit(RXRPC_CALL_TX_NO_MORE, &call->flags)) {
+	if (unlikely(test_bit(RXRPC_CALL_TX_NO_MORE, &call->flags))) {
 		trace_rxrpc_abort(call->debug_id, rxrpc_sendmsg_late_send,
 				  call->cid, call->call_id, call->rx_consumed,
 				  0, -EPROTO);
 		return -EPROTO;
 	}
+	if (unlikely(test_bit(RXRPC_CALL_TX_ERROR, &call->flags))) {
+		trace_rxrpc_abort(call->debug_id, rxrpc_sendmsg_tx_error,
+				  call->cid, call->call_id, call->rx_consumed,
+				  0, -EIO);
+		return -EIO;
+	}
 
 	timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
 
@@ -440,12 +446,21 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
 		/* add the packet to the send queue if it's now full */
 		if (!txb->space ||
 		    (msg_data_left(msg) == 0 && !more)) {
-			if (msg_data_left(msg) == 0 && !more)
-				txb->flags |= RXRPC_LAST_PACKET;
-
+			/* Do any required crypto.  If this fails, it could
+			 * have corrupted the txbuf content with a partial
+			 * encrypt.  Assume that ENOMEM is retryable, but
+			 * everything else is terminal.
+			 */
 			ret = call->security->secure_packet(call, txb);
-			if (ret < 0)
+			if (ret < 0) {
+				if (ret == -ENOMEM)
+					goto maybe_error_rewind;
+				set_bit(RXRPC_CALL_TX_ERROR, &call->flags);
 				goto out;
+			}
+
+			if (msg_data_left(msg) == 0 && !more)
+				txb->flags |= RXRPC_LAST_PACKET;
 			rxrpc_queue_packet(rx, call, txb, notify_end_tx);
 			txb = NULL;
 		}
@@ -463,6 +478,20 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
 	_leave(" = %d", call->error);
 	return call->error;
 
+maybe_error_rewind:
+	/* If we got a retryable error after copying all the supplied data into
+	 * the last packet, we need to rewind the buffer by one byte so the
+	 * caller knows they need to retry.
+	 */
+	if (copied && !more && !msg_data_left(msg)) {
+		txb->space  += 1;
+		txb->len    -= 1;
+		txb->offset -= 1;
+		copied      -= 1;
+		if (call->tx_total_len != -1)
+			call->tx_total_len += 1;
+		iov_iter_revert(&msg->msg_iter, 1);
+	}
 maybe_error:
 	if (copied) {
 		if (rxrpc_call_is_complete(call) &&