Merge #5856

5856: Fix receiving IPv6 packets after IPv4 ones on Linux r=def- a=heinrich5991

Previously, the socket addresses were truncated as the `msg_namelen` field is both input **and** output: After receiving an IPv4 packet, the socket address field would be too short for an IPv6 address.

## Checklist

- [ ] Tested the change ingame
- [ ] Provided screenshots if it is a visual change
- [ ] Tested in combination with possibly related configuration options
- [x] Written a unit test (especially base/) or added coverage to integration test
- [ ] Considered possible null pointers and out of bounds array indexing
- [ ] Changed no physics that affect existing maps
- [ ] Tested the change with [ASan+UBSan or valgrind's memcheck](https://github.com/ddnet/ddnet/#using-addresssanitizer--undefinedbehavioursanitizer-or-valgrinds-memcheck) (optional)


Co-authored-by: heinrich5991 <heinrich5991@gmail.com>

CMakeLists.txt

@@ -2519,6 +2519,7 @@ if(GTEST_FOUND OR DOWNLOAD_GTEST)
     json.cpp
     mapbugs.cpp
     name_ban.cpp
+    net.cpp
     netaddr.cpp
     os.cpp
     packer.cpp

src/base/system.cpp

@@ -149,6 +149,7 @@ typedef struct
 } NETSOCKET_BUFFER;
 
 void net_buffer_init(NETSOCKET_BUFFER *buffer);
+void net_buffer_reinit(NETSOCKET_BUFFER *buffer);
 void net_buffer_simple(NETSOCKET_BUFFER *buffer, char **buf, int *size);
 
 struct NETSOCKET_INTERNAL
@@ -1698,6 +1699,16 @@ void net_buffer_init(NETSOCKET_BUFFER *buffer)
 #endif
 }
 
+void net_buffer_reinit(NETSOCKET_BUFFER *buffer)
+{
+#if defined(CONF_PLATFORM_LINUX)
+	for(int i = 0; i < VLEN; i++)
+	{
+		buffer->msgs[i].msg_hdr.msg_namelen = sizeof(buffer->sockaddrs[i]);
+	}
+#endif
+}
+
 void net_buffer_simple(NETSOCKET_BUFFER *buffer, char **buf, int *size)
 {
 #if defined(CONF_PLATFORM_LINUX)
@@ -1719,6 +1730,7 @@ int net_udp_recv(NETSOCKET sock, NETADDR *addr, unsigned char **data)
 	{
 		if(sock->buffer.pos >= sock->buffer.size)
 		{
+			net_buffer_reinit(&sock->buffer);
 			sock->buffer.size = recvmmsg(sock->ipv4sock, sock->buffer.msgs, VLEN, 0, NULL);
 			sock->buffer.pos = 0;
 		}
@@ -1728,6 +1740,7 @@ int net_udp_recv(NETSOCKET sock, NETADDR *addr, unsigned char **data)
 	{
 		if(sock->buffer.pos >= sock->buffer.size)
 		{
+			net_buffer_reinit(&sock->buffer);
 			sock->buffer.size = recvmmsg(sock->ipv6sock, sock->buffer.msgs, VLEN, 0, NULL);
 			sock->buffer.pos = 0;
 		}

src/test/net.cpp

@@ -0,0 +1,47 @@
+#include <gtest/gtest.h>
+
+#include <base/system.h>
+
+TEST(Net, Ipv4AndIpv6Work)
+{
+	NETADDR Bindaddr = {};
+	NETSOCKET Socket1;
+	NETSOCKET Socket2;
+
+	Bindaddr.type = NETTYPE_IPV4 | NETTYPE_IPV6;
+	Socket2 = net_udp_create(Bindaddr);
+	do
+	{
+		Bindaddr.port = secure_rand() % 64511 + 1024;
+	} while(!(Socket1 = net_udp_create(Bindaddr)));
+
+	NETADDR LocalhostV4;
+	NETADDR LocalhostV6;
+	NETADDR TargetV4;
+	NETADDR TargetV6;
+	ASSERT_FALSE(net_addr_from_str(&LocalhostV4, "127.0.0.1"));
+	ASSERT_FALSE(net_addr_from_str(&LocalhostV6, "[::1]"));
+	TargetV4 = LocalhostV4;
+	TargetV6 = LocalhostV6;
+	TargetV4.port = Bindaddr.port;
+	TargetV6.port = Bindaddr.port;
+
+	NETADDR Addr;
+	unsigned char *pData;
+
+	EXPECT_EQ(net_udp_send(Socket2, &TargetV4, "abc", 3), 3);
+
+	EXPECT_EQ(net_socket_read_wait(Socket1, 10000000), 1);
+	ASSERT_EQ(net_udp_recv(Socket1, &Addr, &pData), 3);
+	Addr.port = 0;
+	EXPECT_EQ(Addr, LocalhostV4);
+	EXPECT_EQ(mem_comp(pData, "abc", 3), 0);
+
+	EXPECT_EQ(net_udp_send(Socket2, &TargetV6, "def", 3), 3);
+
+	EXPECT_EQ(net_socket_read_wait(Socket1, 10000000), 1);
+	ASSERT_EQ(net_udp_recv(Socket1, &Addr, &pData), 3);
+	Addr.port = 0;
+	EXPECT_EQ(Addr, LocalhostV6);
+	EXPECT_EQ(mem_comp(pData, "def", 3), 0);
+}