app_sms: BufferOverflow when receiving odd length 16 bit message

This patch prevents an infinite loop overwriting memory when
a message is received into the unpacksms16() function, where
the length of the message is an odd number of bytes.

(closes issue ASTERISK-22590)
Reported by: Jan Juergens
Tested by: Jan Juergens
........

Merged revisions 403856 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@403857 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_sms.c

@@ -696,7 +696,7 @@ static void unpacksms16(unsigned char *i, unsigned char l, unsigned char *udh, i
 	}
 	while (l--) {
 		int v = *i++;
-		if (l--) {
+		if (l && l--) {
 			v = (v << 8) + *i++;
 		}
 		*o++ = v;
@@ -714,6 +714,7 @@ static int unpacksms(unsigned char dcs, unsigned char *i, unsigned char *udh, in
 	} else if (is8bit(dcs)) {
 		unpacksms8(i, l, udh, udhl, ud, udl, udhi);
 	} else {
+		l += l % 2;
 		unpacksms16(i, l, udh, udhl, ud, udl, udhi);
 	}
 	return l + 1;