Commit 0d698f66 authored by Matt Caswell's avatar Matt Caswell
Browse files

Fix Use After Free for large message sizes 



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: default avatarEmilia Käsper <emilia@openssl.org>
parent f789b04f

ssl/statem/statem.c

+17 −3
Original line number Diff line number Diff line
@@ -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:
@@ -545,8 +560,7 @@ 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

                    && !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);