Handle integer over/under-flow in ast_parse_args

The strtol family of functions will return *_MIN/*_MAX on overflow. To
detect when an overflow has happened, errno must be set to 0 before
calling the function, then checked afterward.

(closes issue ASTERISK-20120)
Reported by: Matt Jordan
Review: https://reviewboard.asterisk.org/r/2073/
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Merged revisions 371392 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 371398 from http://svn.asterisk.org/svn/asterisk/branches/10
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Merged revisions 371399 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@371400 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/config.c

@@ -2827,8 +2827,9 @@ int ast_parse_arg(const char *arg, enum ast_parse_flags flags,
 			error = 1;
 			goto int32_done;
 		}
+		errno = 0;
 		x = strtol(arg, &endptr, 0);
-		if (*endptr || x < INT32_MIN || x > INT32_MAX) {
+		if (*endptr || errno || x < INT32_MIN || x > INT32_MAX) {
 			/* Parse error, or type out of int32_t bounds */
 			error = 1;
 			goto int32_done;
@@ -2881,8 +2882,9 @@ int32_done:
 			error = 1;
 			goto uint32_done;
 		}
+		errno = 0;
 		x = strtoul(arg, &endptr, 0);
-		if (*endptr || x > UINT32_MAX) {
+		if (*endptr || errno || x > UINT32_MAX) {
 			error = 1;
 			goto uint32_done;
 		}