unescape: avoid integer overflow

CVE-2016-8622

Bug: https://curl.haxx.se/docs/adv_20161102H.html
Reported-by: Cure53

3 files changed, 18 insertions, 9 deletions

diff --git a/docs/libcurl/curl_easy_unescape.3 b/docs/libcurl/curl_easy_unescape.3
index 06fd6fcb5..50ce97db7 100644
--- a/docs/libcurl/curl_easy_unescape.3
+++ b/docs/libcurl/curl_easy_unescape.3
@@ -5,7 +5,7 @@
 .\" *                            | (__| |_| |  _ <| |___
 .\" *                             \___|\___/|_| \_\_____|
 .\" *
-.\" * Copyright (C) 1998 - 2015, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" * Copyright (C) 1998 - 2016, 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
@@ -40,7 +40,10 @@ will use strlen() on the input \fIurl\fP string to find out the size.
 
 If \fBoutlength\fP is non-NULL, the function will write the length of the
 returned string in the integer it points to. This allows an escaped string
-containing %00 to still get used properly after unescaping.
+containing %00 to still get used properly after unescaping. Since this is a
+pointer to an \fIint\fP type, it can only return a value up to INT_MAX so no
+longer string can be unescaped if the string length is returned in this
+parameter.
 
 You must \fIcurl_free(3)\fP the returned string when you're done with it.
 .SH AVAILABILITY
diff --git a/lib/dict.c b/lib/dict.c
index a7b5965bd..48a4e0a81 100644
--- a/lib/dict.c
+++ b/lib/dict.c
@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2015, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2016, 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
@@ -52,7 +52,7 @@
 #include <curl/curl.h>
 #include "transfer.h"
 #include "sendf.h"
-
+#include "escape.h"
 #include "progress.h"
 #include "strequal.h"
 #include "dict.h"
@@ -96,12 +96,12 @@ static char *unescape_word(struct Curl_easy *data, const char *inputbuff)
   char *newp;
   char *dictp;
   char *ptr;
-  int len;
+  size_t len;
   char ch;
   int olen=0;
 
-  newp = curl_easy_unescape(data, inputbuff, 0, &len);
-  if(!newp)
+  CURLcode result = Curl_urldecode(data, inputbuff, 0, &newp, &len, FALSE);
+  if(!newp || result)
     return NULL;
 
   dictp = malloc(((size_t)len)*2 + 1); /* add one for terminating zero */
diff --git a/lib/escape.c b/lib/escape.c
index e61260d7c..66570076e 100644
--- a/lib/escape.c
+++ b/lib/escape.c
@@ -224,8 +224,14 @@ char *curl_easy_unescape(struct Curl_easy *data, const char *string,
                                   FALSE);
     if(res)
       return NULL;
-    if(olen)
-      *olen = curlx_uztosi(outputlen);
+
+    if(olen) {
+      if(outputlen <= (size_t) INT_MAX)
+        *olen = curlx_uztosi(outputlen);
+      else
+        /* too large to return in an int, fail! */
+        Curl_safefree(str);
+    }
   }
   return str;
 }