netdev - [PATCH 2/2] appletalk: Improve handling of broadcast packets

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Date:   Wed, 22 Jul 2020 13:37:52 +0200
From:   Vincent Duvert <vincent.ldev@...ert.net>
To:     netdev@...r.kernel.org
Cc:     Vincent Duvert <vincent.ldev@...ert.net>
Subject: [PATCH 2/2] appletalk: Improve handling of broadcast packets

When a broadcast AppleTalk packet is received, prefer queuing it on the
socket whose address matches the address of the interface that received
the packet (and is listening on the correct port). Userspace
applications that handle such packets will usually send a response on
the same socket that received the packet; this fix allows the response
to be sent on the correct interface.

If a socket matching the interface's address is not found, an arbitrary
socket listening on the correct port will be used, if any. This matches
the implementation's previous behavior.

Fixes atalkd's responses to network information requests when multiple
network interfaces are configured to use AppleTalk.

Signed-off-by: Vincent Duvert <vincent.ldev@...ert.net>
---
 net/appletalk/ddp.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/net/appletalk/ddp.c b/net/appletalk/ddp.c
index 15787e8c0629..9d19cd03076f 100644
--- a/net/appletalk/ddp.c
+++ b/net/appletalk/ddp.c
@@ -89,6 +89,7 @@ static struct sock *atalk_search_socket(struct sockaddr_at *to,
 					struct atalk_iface *atif)
 {
 	struct sock *s;
+	struct sock *def_socket = NULL;
 
 	read_lock_bh(&atalk_sockets_lock);
 	sk_for_each(s, &atalk_sockets) {
@@ -98,8 +99,20 @@ static struct sock *atalk_search_socket(struct sockaddr_at *to,
 			continue;
 
 		if (to->sat_addr.s_net == ATADDR_ANYNET &&
-		    to->sat_addr.s_node == ATADDR_BCAST)
-			goto found;
+		    to->sat_addr.s_node == ATADDR_BCAST) {
+			if (atif->address.s_node == at->src_node &&
+			    atif->address.s_net == at->src_net) {
+				/* This socket's address matches the address of the interface
+				 * that received the packet -- use it
+				 */
+				goto found;
+			}
+
+			/* Continue searching for a socket matching the interface address,
+			 * but use this socket by default if no other one is found
+			 */
+			def_socket = s;
+		}
 
 		if (to->sat_addr.s_net == at->src_net &&
 		    (to->sat_addr.s_node == at->src_node ||
@@ -116,7 +129,7 @@ static struct sock *atalk_search_socket(struct sockaddr_at *to,
 			goto found;
 		}
 	}
-	s = NULL;
+	s = def_socket;
 found:
 	read_unlock_bh(&atalk_sockets_lock);
 	return s;
-- 
2.20.1