CURL_MAX_INPUT_LENGTH: largest acceptable string input size

This limits all accepted input strings passed to libcurl to be less than
CURL_MAX_INPUT_LENGTH (8000000) bytes, for these API calls:
curl_easy_setopt() and curl_url_set().

The 8000000 number is arbitrary picked and is meant to detect mistakes
or abuse, not to limit actual practical use cases. By limiting the
acceptable string lengths we also reduce the risk of integer overflows
all over.

NOTE: This does not apply to `CURLOPT_POSTFIELDS`.

Test 1559 verifies.

Closes #3805

lib/setopt.c

@@ -61,6 +61,13 @@ CURLcode Curl_setstropt(char **charp, const char *s)
   if(s) {
     char *str = strdup(s);
 
+    if(str) {
+      size_t len = strlen(str);
+      if(len > CURL_MAX_INPUT_LENGTH) {
+        free(str);
+        return CURLE_BAD_FUNCTION_ARGUMENT;
+      }
+    }
     if(!str)
       return CURLE_OUT_OF_MEMORY;
 

lib/urlapi.c

@@ -642,6 +642,10 @@ static CURLUcode seturl(const char *url, CURLU *u, unsigned int flags)
    ************************************************************/
   /* allocate scratch area */
   urllen = strlen(url);
+  if(urllen > CURL_MAX_INPUT_LENGTH)
+    /* excessive input length */
+    return CURLUE_MALFORMED_INPUT;
+
   path = u->scratch = malloc(urllen * 2 + 2);
   if(!path)
     return CURLUE_OUT_OF_MEMORY;
@@ -1279,6 +1283,10 @@ CURLUcode curl_url_set(CURLU *u, CURLUPart what,
     const char *newp = part;
     size_t nalloc = strlen(part);
 
+    if(nalloc > CURL_MAX_INPUT_LENGTH)
+      /* excessive input length */
+      return CURLUE_MALFORMED_INPUT;
+
     if(urlencode) {
       const unsigned char *i;
       char *o;

lib/urldata.h

@@ -79,6 +79,10 @@
 */
 #define RESP_TIMEOUT (120*1000)
 
+/* Max string intput length is a precaution against abuse and to detect junk
+   input easier and better. */
+#define CURL_MAX_INPUT_LENGTH 8000000
+
 #include "cookie.h"
 #include "psl.h"
 #include "formdata.h"