urldata: make magic be the first struct field

By making the `magic` identifier the same size and at the same place
within the structs (easy, multi, share), libcurl will be able to more
reliably detect and safely error out if an application passes in the
wrong handle to APIs. Easier to detect and less likely to cause crashes
if done.

Such mixups can't be detected at compile-time due to them being
typedefed void pointers - unless `CURL_STRICTER` is defined.

Closes #6484

diff --git a/lib/multi.c b/lib/multi.c
index 57c2ae8c0e3140d22bb252c12c7828e5c9131b9d..d8de7e8e344c31bee0dce6c6b75ee3fa0685cd6c 100644 (file)
--- a/lib/multi.c
+++ b/lib/multi.c
@@ -69,7 +69,7 @@
 #define CURL_MULTI_HANDLE 0x000bab1e
 
 #define GOOD_MULTI_HANDLE(x) \
-  ((x) && (x)->type == CURL_MULTI_HANDLE)
+  ((x) && (x)->magic == CURL_MULTI_HANDLE)
 
 static CURLMcode singlesocket(struct Curl_multi *multi,
                               struct Curl_easy *data);
@@ -360,7 +360,7 @@ struct Curl_multi *Curl_multi_handle(int hashsize, /* socket hash */
   if(!multi)
     return NULL;
 
-  multi->type = CURL_MULTI_HANDLE;
+  multi->magic = CURL_MULTI_HANDLE;
 
   if(Curl_mk_dnscache(&multi->hostcache))
     goto error;
@@ -2453,7 +2453,7 @@ CURLMcode curl_multi_cleanup(struct Curl_multi *multi)
     if(multi->in_callback)
       return CURLM_RECURSIVE_API_CALL;
 
-    multi->type = 0; /* not good anymore */
+    multi->magic = 0; /* not good anymore */
 
     /* Firsrt remove all remaining easy handles */
     data = multi->easyp;

diff --git a/lib/multihandle.h b/lib/multihandle.h
index aa9ca4bcd2925e98c7afffec88ef49216c229b29..f28c5899b6b9d612ec95b23ce1042fd1edbc4a0f 100644 (file)
--- a/lib/multihandle.h
+++ b/lib/multihandle.h
@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2021, 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
@@ -83,7 +83,7 @@ typedef enum {
 struct Curl_multi {
   /* First a simple identifier to easier detect if a user mix up
      this multi handle with an easy handle. Set this to CURL_MULTI_HANDLE. */
-  long type;
+  unsigned int magic;
 
   /* We have a doubly-linked list with easy handles */
   struct Curl_easy *easyp;

diff --git a/lib/setopt.c b/lib/setopt.c
index 731ffeb360feefc8d17ca2f2007f246cb6c1fd7a..409234fcd56ae3cc92e37dc5056292717f62d619 100644 (file)
--- a/lib/setopt.c
+++ b/lib/setopt.c
@@ -2169,8 +2169,9 @@ CURLcode Curl_vsetopt(struct Curl_easy *data, CURLoption option, va_list param)
       data->share = NULL;
     }
 
-    /* use new share if it set */
-    data->share = set;
+    if(GOOD_SHARE_HANDLE(set))
+      /* use new share if it set */
+      data->share = set;
     if(data->share) {
 
       Curl_share_lock(data, CURL_LOCK_DATA_SHARE, CURL_LOCK_ACCESS_SINGLE);

diff --git a/lib/share.c b/lib/share.c
index 5ce9830335a3df44e5a277a432259960b032c02d..4f1804dbd2bffb17c99881f10bb3397b819908bf 100644 (file)
--- a/lib/share.c
+++ b/lib/share.c
@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2021, 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
@@ -37,6 +37,7 @@ curl_share_init(void)
 {
   struct Curl_share *share = calloc(1, sizeof(struct Curl_share));
   if(share) {
+    share->magic = CURL_GOOD_SHARE;
     share->specifier |= (1<<CURL_LOCK_DATA_SHARE);
 
     if(Curl_mk_dnscache(&share->hostcache)) {
@@ -59,6 +60,9 @@ curl_share_setopt(struct Curl_share *share, CURLSHoption option, ...)
   void *ptr;
   CURLSHcode res = CURLSHE_OK;
 
+  if(!GOOD_SHARE_HANDLE(share))
+    return CURLSHE_INVALID;
+
   if(share->dirty)
     /* don't allow setting options while one or more handles are already
        using this share */
@@ -184,7 +188,7 @@ curl_share_setopt(struct Curl_share *share, CURLSHoption option, ...)
 CURLSHcode
 curl_share_cleanup(struct Curl_share *share)
 {
-  if(share == NULL)
+  if(!GOOD_SHARE_HANDLE(share))
     return CURLSHE_INVALID;
 
   if(share->lockfunc)
@@ -218,6 +222,7 @@ curl_share_cleanup(struct Curl_share *share)
 
   if(share->unlockfunc)
     share->unlockfunc(NULL, CURL_LOCK_DATA_SHARE, share->clientdata);
+  share->magic = 0;
   free(share);
 
   return CURLSHE_OK;

diff --git a/lib/share.h b/lib/share.h
index 01aa9cda5995c37ed64296acf93d8919b8cdfb61..222e34ba6ea0abe5b169abeacdbbb63e9fc77041 100644 (file)
--- a/lib/share.h
+++ b/lib/share.h
@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2021, 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
@@ -37,8 +37,12 @@
 #define CURL_VOLATILE volatile
 #endif
 
+#define CURL_GOOD_SHARE 0x7e117a1e
+#define GOOD_SHARE_HANDLE(x) ((x) && (x)->magic == CURL_GOOD_SHARE)
+
 /* this struct is libcurl-private, don't export details */
 struct Curl_share {
+  unsigned int magic; /* CURL_GOOD_SHARE */
   unsigned int specifier;
   CURL_VOLATILE unsigned int dirty;
 

diff --git a/lib/urldata.h b/lib/urldata.h
index 072caf002323dfa13dd44c2bea990b76f47ac368..1aa58507724b68d9ba014729a96998afec757f2e 100644 (file)
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -1884,6 +1884,10 @@ struct Names {
  */
 
 struct Curl_easy {
+  /* First a simple identifier to easier detect if a user mix up this easy
+     handle with a multi handle. Set this to CURLEASY_MAGIC_NUMBER */
+  unsigned int magic;
+
   /* first, two fields for the linked list of these */
   struct Curl_easy *next;
   struct Curl_easy *prev;
@@ -1947,7 +1951,6 @@ struct Curl_easy {
 #ifdef USE_HYPER
   struct hyptransfer hyp;
 #endif
-  unsigned int magic;          /* set to a CURLEASY_MAGIC_NUMBER */
 };
 
 #define LIBCURL_NAME "libcurl"