Check for ClientHello message overruns

The ClientHello processing is insufficiently rigorous in its checks to make
sure that we don't read past the end of the message. This does not have
security implications due to the size of the underlying buffer - but still
needs to be fixed.

With thanks to Qinghao Tang for reporting this issue.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(cherry picked from commit c9642eb1ff79a30e2c7632ef8267cc34cc2b0d79)

diff --git a/ssl/s3_srvr.c b/ssl/s3_srvr.c
index f7ffa0672589d6ba5692ef5b54f156ee2bdc0f3b..00bc757b2b0f31e1cd8b6976e1aca68b7c796df7 100644 (file)
--- a/ssl/s3_srvr.c
+++ b/ssl/s3_srvr.c
@@ -930,6 +930,16 @@ int ssl3_get_client_hello(SSL *s)
     s->first_packet = 0;
     d = p = (unsigned char *)s->init_msg;
 
+    /*
+     * 2 bytes for client version, SSL3_RANDOM_SIZE bytes for random, 1 byte
+     * for session id length
+     */
+    if (n < 2 + SSL3_RANDOM_SIZE + 1) {
+        al = SSL_AD_DECODE_ERROR;
+        SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT);
+        goto f_err;
+    }
+
     /*
      * use version from inside client hello, not from record header (may
      * differ: see RFC 2246, Appendix E, second paragraph)
@@ -962,6 +972,12 @@ int ssl3_get_client_hello(SSL *s)
         unsigned int session_length, cookie_length;
 
         session_length = *(p + SSL3_RANDOM_SIZE);
+
+        if (p + SSL3_RANDOM_SIZE + session_length + 1 >= d + n) {
+            al = SSL_AD_DECODE_ERROR;
+            SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT);
+            goto f_err;
+        }
         cookie_length = *(p + SSL3_RANDOM_SIZE + session_length + 1);
 
         if (cookie_length == 0)
@@ -975,6 +991,12 @@ int ssl3_get_client_hello(SSL *s)
     /* get the session-id */
     j = *(p++);
 
+    if (p + j > d + n) {
+        al = SSL_AD_DECODE_ERROR;
+        SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT);
+        goto f_err;
+    }
+
     s->hit = 0;
     /*
      * Versions before 0.9.7 always allow clients to resume sessions in
@@ -1019,8 +1041,19 @@ int ssl3_get_client_hello(SSL *s)
 
     if (SSL_IS_DTLS(s)) {
         /* cookie stuff */
+        if (p + 1 > d + n) {
+            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) {
+            al = SSL_AD_DECODE_ERROR;
+            SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT);
+            goto f_err;
+        }
+
         /*
          * The ClientHello may contain a cookie even if the
          * HelloVerify message has not been sent--make sure that it
@@ -1086,6 +1119,11 @@ int ssl3_get_client_hello(SSL *s)
         }
     }
 
+    if (p + 2 > d + n) {
+        al = SSL_AD_DECODE_ERROR;
+        SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT);
+        goto f_err;
+    }
     n2s(p, i);
     if ((i == 0) && (j != 0)) {
         /* we need a cipher if we are not resuming a session */
@@ -1093,7 +1131,9 @@ int ssl3_get_client_hello(SSL *s)
         SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_NO_CIPHERS_SPECIFIED);
         goto f_err;
     }
-    if ((p + i) >= (d + n)) {
+
+    /* i bytes of cipher data + 1 byte for compression length later */
+    if ((p + i + 1) > (d + n)) {
         /* not enough data */
         al = SSL_AD_DECODE_ERROR;
         SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_MISMATCH);