cookies: reject oversized cookies

... instead of truncating them.

There's no fixed limit for acceptable cookie names in RFC 6265, but the
entire cookie is said to be less than 4096 bytes (section 6.1). This is
also what browsers seem to implement.

We now allow max 5000 bytes cookie header. Max 4095 bytes length per
cookie name and value. Name + value together may not exceed 4096 bytes.

Added test 1151 to verify

Bug: https://curl.haxx.se/mail/lib-2017-09/0062.html
Reported-by: Kevin Smith

Closes #1894

2 files changed, 27 insertions, 11 deletions

diff --git a/lib/cookie.c b/lib/cookie.c
index 14defe883..1231882ed 100644
--- a/lib/cookie.c
+++ b/lib/cookie.c
@@ -375,7 +375,6 @@ Curl_cookie_add(struct Curl_easy *data,
                                        unless set */
 {
   struct Cookie *clist;
-  char name[MAX_NAME];
   struct Cookie *co;
   struct Cookie *lastc = NULL;
   time_t now = time(NULL);
@@ -397,12 +396,14 @@ Curl_cookie_add(struct Curl_easy *data,
 
   if(httpheader) {
     /* This line was read off a HTTP-header */
+    char name[MAX_NAME];
+    char what[MAX_NAME];
     const char *ptr;
     const char *semiptr;
-    char *what;
 
-    what = malloc(MAX_COOKIE_LINE);
-    if(!what) {
+    size_t linelength = strlen(lineptr);
+    if(linelength > MAX_COOKIE_LINE) {
+      /* discard overly long lines at once */
       free(co);
       return NULL;
     }
@@ -417,7 +418,7 @@ Curl_cookie_add(struct Curl_easy *data,
       /* we have a <what>=<this> pair or a stand-alone word here */
       name[0] = what[0] = 0; /* init the buffers */
       if(1 <= sscanf(ptr, "%" MAX_NAME_TXT "[^;\r\n=] =%"
-                     MAX_COOKIE_LINE_TXT "[^;\r\n]",
+                     MAX_NAME_TXT "[^;\r\n]",
                      name, what)) {
         /* Use strstore() below to properly deal with received cookie
            headers that have the same string property set more than once,
@@ -429,6 +430,20 @@ Curl_cookie_add(struct Curl_easy *data,
         size_t nlen = strlen(name);
         const char *endofn = &ptr[ nlen ];
 
+        infof(data, "cookie size: name/val %d + %d bytes\n",
+              nlen, len);
+
+        if(nlen >= (MAX_NAME-1) || len >= (MAX_NAME-1) ||
+           ((nlen + len) > MAX_NAME)) {
+          /* too long individual name or contents, or too long combination of
+             name + contents. Chrome and Firefox support 4095 or 4096 bytes
+             combo. */
+          free(co);
+          infof(data, "oversized cookie dropped, name/val %d + %d bytes\n",
+                nlen, len);
+          return NULL;
+        }
+
         /* name ends with a '=' ? */
         sep = (*endofn == '=')?TRUE:FALSE;
 
@@ -659,8 +674,6 @@ Curl_cookie_add(struct Curl_easy *data,
       }
     }
 
-    free(what);
-
     if(badcookie || !co->name) {
       /* we didn't get a cookie name or a bad one,
          this is an illegal line, bail out */
diff --git a/lib/cookie.h b/lib/cookie.h
index a9a45785c..cb50b71c6 100644
--- a/lib/cookie.h
+++ b/lib/cookie.h
@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -62,13 +62,16 @@ struct CookieInfo {
    that comprise the cookie non-terminal in the syntax description of the
    Set-Cookie header)"
 
+   We allow max 5000 bytes cookie header. Max 4095 bytes length per cookie
+   name and value. Name + value may not exceed 4096 bytes.
+
 */
 #define MAX_COOKIE_LINE 5000
 #define MAX_COOKIE_LINE_TXT "4999"
 
-/* This is the maximum length of a cookie name we deal with: */
-#define MAX_NAME 1024
-#define MAX_NAME_TXT "1023"
+/* This is the maximum length of a cookie name or content we deal with: */
+#define MAX_NAME 4096
+#define MAX_NAME_TXT "4095"
 
 struct Curl_easy;
 /*