Avoid some undefined pointer arithmetic

A common idiom in the codebase is:

if (p + len > limit)
{
    return; /* Too long */
}

Where "p" points to some malloc'd data of SIZE bytes and
limit == p + SIZE

"len" here could be from some externally supplied data (e.g. from a TLS
message).

The rules of C pointer arithmetic are such that "p + len" is only well
defined where len <= SIZE. Therefore the above idiom is actually
undefined behaviour.

For example this could cause problems if some malloc implementation
provides an address for "p" such that "p + len" actually overflows for
values of len that are too big and therefore p + len < limit!

Issue reported by Guido Vranken.

CVE-2016-2177

Reviewed-by: Rich Salz <rsalz@openssl.org>

diff --git a/ssl/s3_srvr.c b/ssl/s3_srvr.c
index 04cf93a0f7c683e694f9ec99ec9b061266869497..6c74caa33d39004089d4db2eefd96f794df24325 100644 (file)
--- a/ssl/s3_srvr.c
+++ b/ssl/s3_srvr.c
@@ -1040,7 +1040,7 @@ int ssl3_get_client_hello(SSL *s)
 
         session_length = *(p + SSL3_RANDOM_SIZE);
 
-        if (p + SSL3_RANDOM_SIZE + session_length + 1 >= d + n) {
+        if (SSL3_RANDOM_SIZE + session_length + 1 >= (d + n) - p) {
             al = SSL_AD_DECODE_ERROR;
             SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT);
             goto f_err;
@@ -1058,7 +1058,7 @@ int ssl3_get_client_hello(SSL *s)
     /* get the session-id */
     j = *(p++);
 
-    if (p + j > d + n) {
+    if ((d + n) - p < j) {
         al = SSL_AD_DECODE_ERROR;
         SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT);
         goto f_err;
@@ -1114,14 +1114,14 @@ int ssl3_get_client_hello(SSL *s)
 
     if (s->version == DTLS1_VERSION || s->version == DTLS1_BAD_VER) {
         /* cookie stuff */
-        if (p + 1 > d + n) {
+        if ((d + n) - p < 1) {
             al = SSL_AD_DECODE_ERROR;
             SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT);
             goto f_err;
         }
         cookie_len = *(p++);
 
-        if (p + cookie_len > d + n) {
+        if ((d + n ) - p < cookie_len) {
             al = SSL_AD_DECODE_ERROR;
             SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT);
             goto f_err;
@@ -1166,7 +1166,7 @@ int ssl3_get_client_hello(SSL *s)
         p += cookie_len;
     }
 
-    if (p + 2 > d + n) {
+    if ((d + n ) - p < 2) {
         al = SSL_AD_DECODE_ERROR;
         SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT);
         goto f_err;
@@ -1180,7 +1180,7 @@ int ssl3_get_client_hello(SSL *s)
     }
 
     /* i bytes of cipher data + 1 byte for compression length later */
-    if ((p + i + 1) > (d + n)) {
+    if ((d + n) - p < i + 1) {
         /* not enough data */
         al = SSL_AD_DECODE_ERROR;
         SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_MISMATCH);
@@ -1246,7 +1246,7 @@ int ssl3_get_client_hello(SSL *s)
 
     /* compression */
     i = *(p++);
-    if ((p + i) > (d + n)) {
+    if ((d + n) - p < i) {
         /* not enough data */
         al = SSL_AD_DECODE_ERROR;
         SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_MISMATCH);

diff --git a/ssl/ssl_sess.c b/ssl/ssl_sess.c
index 48fc4511f1fe8dbaef5dea6b8f6c7983a48c9f0e..a97d0602ef4efca8d1dd895a601f7d05b329ea4f 100644 (file)
--- a/ssl/ssl_sess.c
+++ b/ssl/ssl_sess.c
@@ -602,7 +602,7 @@ int ssl_get_prev_session(SSL *s, unsigned char *session_id, int len,
     int r;
 #endif
 
-    if (session_id + len > limit) {
+    if (limit - session_id < len) {
         fatal = 1;
         goto err;
     }

diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index 0bdb77d49fc311a9434e731e22bb1b3d913ab6d2..8ed179330565514c75b997e0ce93e11eda7bb919 100644 (file)
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -942,11 +942,11 @@ static void ssl_check_for_safari(SSL *s, const unsigned char *data,
         0x02, 0x03,             /* SHA-1/ECDSA */
     };
 
-    if (data >= (limit - 2))
+    if (limit - data <= 2)
         return;
     data += 2;
 
-    if (data > (limit - 4))
+    if (limit - data < 4)
         return;
     n2s(data, type);
     n2s(data, size);
@@ -954,7 +954,7 @@ static void ssl_check_for_safari(SSL *s, const unsigned char *data,
     if (type != TLSEXT_TYPE_server_name)
         return;
 
-    if (data + size > limit)
+    if (limit - data < size)
         return;
     data += size;
 
@@ -962,7 +962,7 @@ static void ssl_check_for_safari(SSL *s, const unsigned char *data,
         const size_t len1 = sizeof(kSafariExtensionsBlock);
         const size_t len2 = sizeof(kSafariTLS12ExtensionsBlock);
 
-        if (data + len1 + len2 != limit)
+        if (limit - data != (int)(len1 + len2))
             return;
         if (memcmp(data, kSafariExtensionsBlock, len1) != 0)
             return;
@@ -971,7 +971,7 @@ static void ssl_check_for_safari(SSL *s, const unsigned char *data,
     } else {
         const size_t len = sizeof(kSafariExtensionsBlock);
 
-        if (data + len != limit)
+        if (limit - data != (int)(len))
             return;
         if (memcmp(data, kSafariExtensionsBlock, len) != 0)
             return;
@@ -1019,19 +1019,19 @@ int ssl_parse_clienthello_tlsext(SSL *s, unsigned char **p,
     if (data == limit)
         goto ri_check;
 
-    if (data > (limit - 2))
+    if (limit - data < 2)
         goto err;
 
     n2s(data, len);
 
-    if (data + len != limit)
+    if (limit - data != len)
         goto err;
 
-    while (data <= (limit - 4)) {
+    while (limit - data >= 4) {
         n2s(data, type);
         n2s(data, size);
 
-        if (data + size > (limit))
+        if (limit - data < size)
             goto err;
 # if 0
         fprintf(stderr, "Received extension type %d size %d\n", type, size);
@@ -1460,20 +1460,20 @@ int ssl_parse_serverhello_tlsext(SSL *s, unsigned char **p, unsigned char *d,
                              SSL_TLSEXT_HB_DONT_SEND_REQUESTS);
 # endif
 
-    if (data >= (d + n - 2))
+    if ((d + n) - data <= 2)
         goto ri_check;
 
     n2s(data, length);
-    if (data + length != d + n) {
+    if ((d + n) - data != length) {
         *al = SSL_AD_DECODE_ERROR;
         return 0;
     }
 
-    while (data <= (d + n - 4)) {
+    while ((d + n) - data >= 4) {
         n2s(data, type);
         n2s(data, size);
 
-        if (data + size > (d + n))
+        if ((d + n) - data < size)
             goto ri_check;
 
         if (s->tlsext_debug_cb)
@@ -2179,29 +2179,33 @@ int tls1_process_ticket(SSL *s, unsigned char *session_id, int len,
     /* Skip past DTLS cookie */
     if (s->version == DTLS1_VERSION || s->version == DTLS1_BAD_VER) {
         i = *(p++);
-        p += i;
-        if (p >= limit)
+
+        if (limit - p <= i)
             return -1;
+
+        p += i;
     }
     /* Skip past cipher list */
     n2s(p, i);
-    p += i;
-    if (p >= limit)
+    if (limit - p <= i)
         return -1;
+    p += i;
+
     /* Skip past compression algorithm list */
     i = *(p++);
-    p += i;
-    if (p > limit)
+    if (limit - p < i)
         return -1;
+    p += i;
+
     /* Now at start of extensions */
-    if ((p + 2) >= limit)
+    if (limit - p <= 2)
         return 0;
     n2s(p, i);
-    while ((p + 4) <= limit) {
+    while (limit - p >= 4) {
         unsigned short type, size;
         n2s(p, type);
         n2s(p, size);
-        if (p + size > limit)
+        if (limit - p < size)
             return 0;
         if (type == TLSEXT_TYPE_session_ticket) {
             int r;