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url: fix alignment of ssl_backend_data struct

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- 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
This commit is contained in:
Jay Satiro 2017-11-20 01:26:19 -05:00 committed by Daniel Stenberg
parent c79b2ca03d
commit 9b5e12a549
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GPG Key ID: 5CC908FDB71E12C2
2 changed files with 30 additions and 31 deletions
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51
lib/url.c
View File

@ -1793,15 +1793,41 @@ static void llist_dtor(void *user, void *element)
*/
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 */
@ -1881,23 +1907,6 @@ static struct connectdata *allocate_conn(struct Curl_easy *data)
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;

10
lib/urldata.h
View File

@ -1004,16 +1004,6 @@ struct connectdata {
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. */