Language: C
Label: vulnerable
CWE: CWE-190 \u2014 Integer Overflow or Wraparound
The product performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control.

Code:
JSON_read(int fd)
{
    uint32_t hsize, nsize;
    char *str;
    cJSON *json = NULL;
    int rc;

    /*
     * Read a four-byte integer, which is the length of the JSON to follow.
     * Then read the JSON into a buffer and parse it.  Return a parsed JSON
     * structure, NULL if there was an error.
     */
    if (Nread(fd, (char*) &nsize, sizeof(nsize), Ptcp) >= 0) {
	hsize = ntohl(nsize);
	/* Allocate a buffer to hold the JSON */
	str = (char *) calloc(sizeof(char), hsize+1);	/* +1 for trailing null */
	if (str != NULL) {
	    rc = Nread(fd, str, hsize, Ptcp);
	    if (rc >= 0) {
		/*
		 * We should be reading in the number of bytes corresponding to the
		 * length in that 4-byte integer.  If we don't the socket might have
		 * prematurely closed.  Only do the JSON parsing if we got the
		 * correct number of bytes.
		 */
		if (rc == hsize) {
		    json = cJSON_Parse(str);
		}
		else {
		    printf("WARNING:  Size of data read does not correspond to offered length\n");
		}
	    }
	}
	free(str);
    }
    return json;
}