px5g: creates certificates that expire in the past

the attached patch fixes a bug of px5g when instructed to build
certificates that expire after 2038-01-19, caused a multiplication that
may overflow the "to" variable of type time_t

Attached patch checks if "to" precedes "from": if so sets "to" to its
maximum value. Pretty rude, but works well even if certificate is set to
expire in a century

Signed-off-by: Federico Fissore <federico@fissore.org>
Patchork: http://patchwork.openwrt.org/patch/3749/

SVN-Revision: 37165

package/utils/px5g/src/px5g.c

@@ -22,6 +22,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
+#include <limits.h>
 #include "polarssl/havege.h"
 #include "polarssl/bignum.h"
 #include "polarssl/x509.h"
@@ -157,6 +158,8 @@ int selfsigned(char **arg) {
 	from = (from < 1000000000) ? 1000000000 : from;
 	strftime(fstr, sizeof(fstr), "%F %H:%M:%S", gmtime(&from));
 	to = from + 60 * 60 * 24 * days;
+	if (to < from)
+		to = INT_MAX;
 	strftime(tstr, sizeof(tstr), "%F %H:%M:%S", gmtime(&to));
 
 	x509_raw cert;