Make message buffer slightly larger than message.

Grow TLS/DTLS 16 bytes more than strictly necessary as a precaution against OOB reads. In most cases this will have no effect because the message buffer will be large enough already. Reviewed-by: Matt Caswell <matt@openssl.org> (cherry picked from commit 006a788)
openssl · Sep 21, 2016 · bb1a486 · bb1a486
1 parent 8289755
commit bb1a486
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Showing 2 changed files with 9 additions and 2 deletions.
diff --git a/ssl/d1_both.c b/ssl/d1_both.c
@@ -577,9 +577,12 @@ static int dtls1_preprocess_fragment(SSL *s, struct hm_header_st *msg_hdr,
         /*
          * msg_len is limited to 2^24, but is effectively checked against max
          * above
+         *
+         * Make buffer slightly larger than message length as a precaution
+         * against small OOB reads e.g. CVE-2016-6306
          */
         if (!BUF_MEM_grow_clean
-            (s->init_buf, msg_len + DTLS1_HM_HEADER_LENGTH)) {
+            (s->init_buf, msg_len + DTLS1_HM_HEADER_LENGTH + 16)) {
             SSLerr(SSL_F_DTLS1_PREPROCESS_FRAGMENT, ERR_R_BUF_LIB);
             return SSL_AD_INTERNAL_ERROR;
         }

diff --git a/ssl/s3_both.c b/ssl/s3_both.c
@@ -499,9 +499,13 @@ long ssl3_get_message(SSL *s, int st1, int stn, int mt, long max, int *ok)
             SSLerr(SSL_F_SSL3_GET_MESSAGE, SSL_R_EXCESSIVE_MESSAGE_SIZE);
             goto f_err;
         }
+        /*
+         * Make buffer slightly larger than message length as a precaution
+         * against small OOB reads e.g. CVE-2016-6306
+         */
         if (l
             && !BUF_MEM_grow_clean(s->init_buf,
-                                   (int)l + SSL3_HM_HEADER_LENGTH)) {
+                                   (int)l + SSL3_HM_HEADER_LENGTH + 16)) {
             SSLerr(SSL_F_SSL3_GET_MESSAGE, ERR_R_BUF_LIB);
             goto err;
         }