checksum: use csum_ip4_header() in udp.c and tcp.c

We can find the same function to compute the IPv4 header
checksum in tcp.c, udp.c and tap.c

Use the function defined for tap.c, csum_ip4_header(), but
with the code used in tcp.c and udp.c as it doesn't need a fully
initialiazed IPv4 header, only protocol, tot_len, saddr and daddr.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Message-ID: <20240303135114.1023026-7-lvivier@redhat.com>
[dwg: Fix weird cppcheck regression; it appears to be a problem
 in pre-existing code, but somehow this patch is exposing it]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

checksum.c

@@ -57,6 +57,7 @@
 #include <linux/icmpv6.h>
 
 #include "util.h"
+#include "ip.h"
 #include "checksum.h"
 
 /* Checksums are optional for UDP over IPv4, so we usually just set
@@ -114,13 +115,26 @@ uint16_t csum_fold(uint32_t sum)
 }
 
 /**
- * csum_ip4_header() - Calculate and set IPv4 header checksum
+ * csum_ip4_header() - Calculate IPv4 header checksum
- * @ip4h:	IPv4 header
+ * @tot_len:	IPv4 payload length (data + IP header, network order)
+ * @protocol:	Protocol number (network order)
+ * @saddr:	IPv4 source address (network order)
+ * @daddr:	IPv4 destination address (network order)
+ *
+ * Return: 16-bit folded sum of the IPv4 header
  */
-void csum_ip4_header(struct iphdr *ip4h)
+uint16_t csum_ip4_header(uint16_t tot_len, uint8_t protocol,
+			 struct in_addr saddr, struct in_addr daddr)
 {
-	ip4h->check = 0;
+	uint32_t sum = L2_BUF_IP4_PSUM(protocol);
-	ip4h->check = csum(ip4h, (size_t)ip4h->ihl * 4, 0);
+
+	sum += tot_len;
+	sum += (saddr.s_addr >> 16) & 0xffff;
+	sum += saddr.s_addr & 0xffff;
+	sum += (daddr.s_addr >> 16) & 0xffff;
+	sum += daddr.s_addr & 0xffff;
+
+	return ~csum_fold(sum);
 }
 
 /**

checksum.h

@@ -13,7 +13,8 @@ struct icmp6hdr;
 uint32_t sum_16b(const void *buf, size_t len);
 uint16_t csum_fold(uint32_t sum);
 uint16_t csum_unaligned(const void *buf, size_t len, uint32_t init);
-void csum_ip4_header(struct iphdr *ip4h);
+uint16_t csum_ip4_header(uint16_t tot_len, uint8_t protocol,
+			 struct in_addr saddr, struct in_addr daddr);
 void csum_udp4(struct udphdr *udp4hr,
 	       struct in_addr saddr, struct in_addr daddr,
 	       const void *payload, size_t len);

tap.c

@@ -161,7 +161,7 @@ static void *tap_push_ip4h(char *buf, struct in_addr src, struct in_addr dst,
 	ip4h->protocol = proto;
 	ip4h->saddr = src.s_addr;
 	ip4h->daddr = dst.s_addr;
-	csum_ip4_header(ip4h);
+	ip4h->check = csum_ip4_header(ip4h->tot_len, proto, src, dst);
 	return ip4h + 1;
 }
 

tcp.c

@@ -935,23 +935,6 @@ static void tcp_sock_set_bufsize(const struct ctx *c, int s)
 		trace("TCP: failed to set SO_SNDBUF to %i", v);
 }
 
-/**
- * tcp_update_check_ip4() - Update IPv4 with variable parts from stored one
- * @buf:	L2 packet buffer with final IPv4 header
- */
-static void tcp_update_check_ip4(struct tcp4_l2_buf_t *buf)
-{
-	uint32_t sum = L2_BUF_IP4_PSUM(IPPROTO_TCP);
-
-	sum += buf->iph.tot_len;
-	sum += (buf->iph.saddr >> 16) & 0xffff;
-	sum += buf->iph.saddr & 0xffff;
-	sum += (buf->iph.daddr >> 16) & 0xffff;
-	sum += buf->iph.daddr & 0xffff;
-
-	buf->iph.check = (uint16_t)~csum_fold(sum);
-}
-
 /**
  * tcp_update_check_tcp4() - Update TCP checksum from stored one
  * @buf:	L2 packet buffer with final IPv4 header
@@ -1394,10 +1377,9 @@ do {									\
 		b->iph.saddr = a4->s_addr;
 		b->iph.daddr = c->ip4.addr_seen.s_addr;
 
-		if (check)
+		b->iph.check = check ? *check :
-			b->iph.check = *check;
+			       csum_ip4_header(b->iph.tot_len, IPPROTO_TCP,
-		else
+					       *a4, c->ip4.addr_seen);
-			tcp_update_check_ip4(b);
 
 		SET_TCP_HEADER_COMMON_V4_V6(b, conn, seq);
 

udp.c

@@ -275,23 +275,6 @@ static void udp_invert_portmap(struct udp_fwd_ports *fwd)
 	}
 }
 
-/**
- * udp_update_check4() - Update checksum with variable parts from stored one
- * @buf:	L2 packet buffer with final IPv4 header
- */
-static void udp_update_check4(struct udp4_l2_buf_t *buf)
-{
-	uint32_t sum = L2_BUF_IP4_PSUM(IPPROTO_UDP);
-
-	sum += buf->iph.tot_len;
-	sum += (buf->iph.saddr >> 16) & 0xffff;
-	sum += buf->iph.saddr & 0xffff;
-	sum += (buf->iph.daddr >> 16) & 0xffff;
-	sum += buf->iph.daddr & 0xffff;
-
-	buf->iph.check = (uint16_t)~csum_fold(sum);
-}
-
 /**
  * udp_update_l2_buf() - Update L2 buffers with Ethernet and IPv4 addresses
  * @eth_d:	Ethernet destination address, NULL if unchanged
@@ -619,7 +602,8 @@ static size_t udp_update_hdr4(const struct ctx *c, int n, in_port_t dstport,
 	}
 	b->iph.saddr = src->s_addr;
 
-	udp_update_check4(b);
+	b->iph.check = csum_ip4_header(b->iph.tot_len, IPPROTO_UDP,
+				       *src, c->ip4.addr_seen);
 	b->uh.source = b->s_in.sin_port;
 	b->uh.dest = htons(dstport);
 	b->uh.len = htons(udp4_l2_mh_sock[n].msg_len + sizeof(b->uh));