From 3888095ed2fa32870c2a5452bd91ca21efa70907 Mon Sep 17 00:00:00 2001
From: Jay Satiro <raysatiro@yahoo.com>
Date: Mon, 20 Nov 2017 01:26:19 -0500
Subject: [PATCH] url: fix alignment of ssl_backend_data struct
- Align the array of ssl_backend_data on a max 32 byte boundary.
8 is likely to be ok but I went with 32 for posterity should one of
the ssl_backend_data structs change to contain a larger sized variable
in the future.
Prior to this change (since dev 70f1db3, release 7.56) the connectdata
structure was undersized by 4 bytes in 32-bit builds with ssl enabled
because long long * was mistakenly used for alignment instead of
long long, with the intention being an 8 byte boundary. Also long long
may not be an available type.
The undersized connectdata could lead to oob read/write past the end in
what was expected to be the last 4 bytes of the connection's secondary
socket https proxy ssl_backend_data struct (the secondary socket in a
connection is used by ftp, others?).
Closes https://github.com/curl/curl/issues/2093
CVE-2017-8818
Bug: https://curl.haxx.se/docs/adv_2017-af0a.html
---
lib/url.c | 51 ++++++++++++++++++++++++++++++---------------------
lib/urldata.h | 10 ----------
2 files changed, 30 insertions(+), 31 deletions(-)
diff --git a/lib/url.c b/lib/url.c
index 9f9fa0c43..47f69c9f1 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -1791,19 +1791,45 @@ static void llist_dtor(void *user, void *element)
/*
* Allocate and initialize a new connectdata object.
*/
static struct connectdata *allocate_conn(struct Curl_easy *data)
{
+ struct connectdata *conn;
+ size_t connsize = sizeof(struct connectdata);
+
#ifdef USE_SSL
-#define SSL_EXTRA + 4 * Curl_ssl->sizeof_ssl_backend_data - sizeof(long long)
-#else
-#define SSL_EXTRA 0
+/* SSLBK_MAX_ALIGN: The max byte alignment a CPU would use */
+#define SSLBK_MAX_ALIGN 32
+ /* The SSL backend-specific data (ssl_backend_data) objects are allocated as
+ part of connectdata at the end. To ensure suitable alignment we will
+ assume a maximum of SSLBK_MAX_ALIGN for alignment. Since calloc returns a
+ pointer suitably aligned for any variable this will ensure the
+ ssl_backend_data array has proper alignment, even if that alignment turns
+ out to be less than SSLBK_MAX_ALIGN. */
+ size_t paddingsize = sizeof(struct connectdata) % SSLBK_MAX_ALIGN;
+ size_t alignsize = paddingsize ? (SSLBK_MAX_ALIGN - paddingsize) : 0;
+ size_t sslbksize = Curl_ssl->sizeof_ssl_backend_data;
+ connsize += alignsize + (4 * sslbksize);
#endif
- struct connectdata *conn = calloc(1, sizeof(struct connectdata) + SSL_EXTRA);
+
+ conn = calloc(1, connsize);
if(!conn)
return NULL;
+#ifdef USE_SSL
+ /* Point to the ssl_backend_data objects at the end of connectdata.
+ Note that these backend pointers can be swapped by vtls (eg ssl backend
+ data becomes proxy backend data). */
+ {
+ char *end = (char *)conn + connsize;
+ conn->ssl[0].backend = ((void *)(end - (4 * sslbksize)));
+ conn->ssl[1].backend = ((void *)(end - (3 * sslbksize)));
+ conn->proxy_ssl[0].backend = ((void *)(end - (2 * sslbksize)));
+ conn->proxy_ssl[1].backend = ((void *)(end - (1 * sslbksize)));
+ }
+#endif
+
conn->handler = &Curl_handler_dummy; /* Be sure we have a handler defined
already from start to avoid NULL
situations and checks */
/* and we setup a few fields in case we end up actually using this struct */
@@ -1879,27 +1905,10 @@ static struct connectdata *allocate_conn(struct Curl_easy *data)
conn->proxy_ssl_config.verifypeer = data->set.proxy_ssl.primary.verifypeer;
conn->proxy_ssl_config.verifyhost = data->set.proxy_ssl.primary.verifyhost;
conn->ip_version = data->set.ipver;
-#ifdef USE_SSL
- /*
- * To save on malloc()s, the SSL backend-specific data has been allocated
- * at the end of the connectdata struct.
- */
- {
- char *p = (char *)&conn->align_data__do_not_use;
- conn->ssl[0].backend = (struct ssl_backend_data *)p;
- conn->ssl[1].backend =
- (struct ssl_backend_data *)(p + Curl_ssl->sizeof_ssl_backend_data);
- conn->proxy_ssl[0].backend =
- (struct ssl_backend_data *)(p + Curl_ssl->sizeof_ssl_backend_data * 2);
- conn->proxy_ssl[1].backend =
- (struct ssl_backend_data *)(p + Curl_ssl->sizeof_ssl_backend_data * 3);
- }
-#endif
-
#if !defined(CURL_DISABLE_HTTP) && defined(USE_NTLM) && \
defined(NTLM_WB_ENABLED)
conn->ntlm_auth_hlpr_socket = CURL_SOCKET_BAD;
conn->ntlm_auth_hlpr_pid = 0;
conn->challenge_header = NULL;
diff --git a/lib/urldata.h b/lib/urldata.h
index 94f692223..edd1fd9ac 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -1002,20 +1002,10 @@ struct connectdata {
#ifdef USE_UNIX_SOCKETS
char *unix_domain_socket;
bool abstract_unix_socket;
#endif
-
-#ifdef USE_SSL
- /*
- * To avoid multiple malloc() calls, the ssl_connect_data structures
- * associated with a connectdata struct are allocated in the same block
- * as the latter. This field forces alignment to an 8-byte boundary so
- * that this all works.
- */
- long long *align_data__do_not_use;
-#endif
};
/* The end of connectdata. */
/*
--
2.15.0