rxrpc: Don't transmit an ACK if there's no reason set

Don't transmit an ACK if call->ackr_reason in unset.  There's the
possibility of a race between recvmsg() sending an ACK and the background
processing thread trying to send the same one.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/net/rxrpc/output.c b/net/rxrpc/output.c
index 06a9aca739d1..aa0507214b31 100644
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c
@@ -137,6 +137,11 @@ int rxrpc_send_call_packet(struct rxrpc_call *call, u8 type)
         switch (type) {
         case RXRPC_PACKET_TYPE_ACK:
                 spin_lock_bh(&call->lock);
+                if (!call->ackr_reason) {
+                        spin_unlock_bh(&call->lock);
+                        ret = 0;
+                        goto out;
+                }
                 n = rxrpc_fill_out_ack(call, pkt);
                 call->ackr_reason = 0;