Fix aliasing bug causing in_cksum() to fail on odd packet sizes

due to compiler optimization.

PR:		bin/13292
Suggested by:	wollman

1 files changed, 9 insertions, 5 deletions

diff --git a/sbin/ping/ping.c b/sbin/ping/ping.c
index edbc82a..f96774d 100644
--- a/sbin/ping/ping.c
+++ b/sbin/ping/ping.c
@@ -929,7 +929,10 @@ in_cksum(addr, len)
 	register int nleft = len;
 	register u_short *w = addr;
 	register int sum = 0;
-	u_short answer = 0;
+	union {
+	    u_int16_t us;
+	    u_int8_t  uc[2];
+	} answer;
 
 	/*
 	 * Our algorithm is simple, using a 32 bit accumulator (sum), we add
@@ -943,15 +946,16 @@ in_cksum(addr, len)
 
 	/* mop up an odd byte, if necessary */
 	if (nleft == 1) {
-		*(u_char *)(&answer) = *(u_char *)w ;
-		sum += answer;
+		answer.uc[0] = *(u_char *)w;
+		answer.uc[1] = 0;
+		sum += answer.us;
 	}
 
 	/* add back carry outs from top 16 bits to low 16 bits */
 	sum = (sum >> 16) + (sum & 0xffff);	/* add hi 16 to low 16 */
 	sum += (sum >> 16);			/* add carry */
-	answer = ~sum;				/* truncate to 16 bits */
-	return(answer);
+	answer.us = ~sum;			/* truncate to 16 bits */
+	return(answer.us);
 }
 
 /*