From 0d698f6696e114a6e47f8b75ff88ec81f9e30175 Mon Sep 17 00:00:00 2001 From: Matt Caswell Date: Fri, 23 Sep 2016 16:58:11 +0100 Subject: [PATCH] Fix Use After Free for large message sizes MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The buffer to receive messages is initialised to 16k. If a message is received that is larger than that then the buffer is "realloc'd". This can cause the location of the underlying buffer to change. Anything that is referring to the old location will be referring to free'd data. In the recent commit c1ef7c97 (master) and 4b390b6c (1.1.0) the point in the code where the message buffer is grown was changed. However s->init_msg was not updated to point at the new location. CVE-2016-6309 Reviewed-by: Emilia Käsper --- ssl/statem/statem.c | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-) diff --git a/ssl/statem/statem.c b/ssl/statem/statem.c index 27dd5d62e5..f00480803c 100644 --- a/ssl/statem/statem.c +++ b/ssl/statem/statem.c @@ -445,6 +445,21 @@ static void init_read_state_machine(SSL *s) st->read_state = READ_STATE_HEADER; } +static int grow_init_buf(SSL *s, size_t size) { + + size_t msg_offset = (char *)s->init_msg - s->init_buf->data; + + if (!BUF_MEM_grow_clean(s->init_buf, (int)size)) + return 0; + + if (size < msg_offset) + return 0; + + s->init_msg = s->init_buf->data + msg_offset; + + return 1; +} + /* * This function implements the sub-state machine when the message flow is in * MSG_FLOW_READING. The valid sub-states and transitions are: @@ -545,9 +560,8 @@ static SUB_STATE_RETURN read_state_machine(SSL *s) /* dtls_get_message already did this */ if (!SSL_IS_DTLS(s) && s->s3->tmp.message_size > 0 - && !BUF_MEM_grow_clean(s->init_buf, - (int)s->s3->tmp.message_size - + SSL3_HM_HEADER_LENGTH)) { + && !grow_init_buf(s, s->s3->tmp.message_size + + SSL3_HM_HEADER_LENGTH)) { ssl3_send_alert(s, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR); SSLerr(SSL_F_READ_STATE_MACHINE, ERR_R_BUF_LIB); return SUB_STATE_ERROR; -- 2.25.1