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Avoid buffer over-read on null cipher AEAD 

In the defined AEAD modes, SRTP packets must always be encrypted and
authenticated, but SRTCP packets may be only authenticated.  It's
possible, therefore, for us to end up in `srtp_protect_aead()` without
the `sec_serv_conf` bit being set.  We should just ignore this and
encrypt the RTP packet anyway.

What we are doing instead is encrypting the packet anyway, but setting
`enc_start` to NULL first.  This causes `aad_len` to underflow which
will cause us to over-read in `cipher_set_aad()`.

If we could get past that, we would try to read and write memory
starting at 0x0 down in `cipher_encrypt()`.

This commit causes us to not check the `sec_serv_conf` bit and never
set `enc_start` to NULL in `srtp_protect_aead()`.

`srtp_unprotect_aead()` does not contain a similar error.
This commit is contained in:
Travis Cross 2014-06-29 17:32:33 +00:00
parent 3bf2b9af75
commit 9ea93c4c50
1 changed files with 9 additions and 15 deletions
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24
libs/srtp/srtp/srtp.c
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@ -878,22 +878,16 @@ srtp_protect_aead (srtp_ctx_t *ctx, srtp_stream_ctx_t *stream,
* encrypted - the encrypted portion starts after the rtp header
* extension, if present; otherwise, it starts after the last csrc,
* if any are present
*
* if we're not providing confidentiality, set enc_start to NULL
*/
if (stream->rtp_services & sec_serv_conf) {
enc_start = (uint32_t*)hdr + uint32s_in_rtp_header + hdr->cc;
if (hdr->x == 1) {
srtp_hdr_xtnd_t *xtn_hdr = (srtp_hdr_xtnd_t*)enc_start;
enc_start += (ntohs(xtn_hdr->length) + 1);
}
if (!(enc_start < (uint32_t*)hdr + *pkt_octet_len))
return err_status_parse_err;
enc_octet_len = (unsigned int)(*pkt_octet_len -
((enc_start - (uint32_t*)hdr) << 2));
} else {
enc_start = NULL;
}
enc_start = (uint32_t*)hdr + uint32s_in_rtp_header + hdr->cc;
if (hdr->x == 1) {
srtp_hdr_xtnd_t *xtn_hdr = (srtp_hdr_xtnd_t*)enc_start;
enc_start += (ntohs(xtn_hdr->length) + 1);
}
if (!(enc_start < (uint32_t*)hdr + *pkt_octet_len))
return err_status_parse_err;
enc_octet_len = (unsigned int)(*pkt_octet_len -
((enc_start - (uint32_t*)hdr) << 2));
/*
* estimate the packet index using the start of the replay window