From: guy <guy>
Date: Sat, 23 Dec 2000 20:55:22 +0000 (+0000)
Subject: When adding the last byte of an odd number of bytes to a TCP or UDP
X-Git-Tag: tcpdump-3.5.1~24
X-Git-Url: https://git.tcpdump.org/tcpdump/commitdiff_plain/a329c9ae7cc43ac33a176a7557eec240bca94afa

When adding the last byte of an odd number of bytes to a TCP or UDP
checksum, fetch it by casting the pointer to "const u_int8_t *" rather
than "const char *" - casting it to "const char *" causes it to be
sign-extended, perhaps causing 16 1 bits to be added in at the top and,
at least on big-endian platforms (where "htons()" does nothing, meaning
it won't trim off the extra 16 bits) with signed "char"s (e.g., SPARC),
causing the checksum to be computed incorrectly and causing it to
incorrectly be reported as bad.
---

diff --git a/print-tcp.c b/print-tcp.c
index 852300ce..9cc707fc 100644
--- a/print-tcp.c
+++ b/print-tcp.c
@@ -21,7 +21,7 @@
 
 #ifndef lint
 static const char rcsid[] =
-    "@(#) $Header: /tcpdump/master/tcpdump/print-tcp.c,v 1.80 2000-11-17 19:08:16 itojun Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/tcpdump/print-tcp.c,v 1.81 2000-12-23 20:55:22 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -169,7 +169,7 @@ static int tcp_cksum(register const struct ip *ip,
 		sum += *sp++;
 
 	if (tlen & 1) {
-		sum += htons( (*(const char *)sp) << 8);
+		sum += htons( (*(const u_int8_t *)sp) << 8);
 	}
 
 	while (sum > 0xffff)
@@ -217,7 +217,7 @@ static int tcp6_cksum(const struct ip6_hdr *ip6, const struct tcphdr *tp,
 		sum += *sp++;
 
 	if (tlen & 1)
-		sum += htons((*(const char *)sp) << 8);
+		sum += htons((*(const u_int8_t *)sp) << 8);
 
 	while (sum > 0xffff)
 		sum = (sum & 0xffff) + (sum >> 16);
diff --git a/print-udp.c b/print-udp.c
index a95683ec..c53c319c 100644
--- a/print-udp.c
+++ b/print-udp.c
@@ -21,7 +21,7 @@
 
 #ifndef lint
 static const char rcsid[] =
-    "@(#) $Header: /tcpdump/master/tcpdump/print-udp.c,v 1.89 2000-11-17 19:08:16 itojun Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/tcpdump/print-udp.c,v 1.90 2000-12-23 20:55:22 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -325,7 +325,7 @@ static int udp_cksum(register const struct ip *ip,
 		sum += *sp++;
 
 	if (tlen & 1) {
-		sum += htons( (*(const char *)sp) << 8);
+		sum += htons( (*(const u_int8_t *)sp) << 8);
 	}
 
 	while (sum > 0xffff)
@@ -373,7 +373,7 @@ static int udp6_cksum(const struct ip6_hdr *ip6, const struct udphdr *up,
 		sum += *sp++;
 
 	if (tlen & 1)
-		sum += htons((*(const char *)sp) << 8);
+		sum += htons((*(const u_int8_t *)sp) << 8);
 
 	while (sum > 0xffff)
 		sum = (sum & 0xffff) + (sum >> 16);