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zebra: fix multiple bfd buffer issues

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Whatever this BFD re-transmission function is had a few problems.

1. Used memcpy instead of the (more concise) stream APIs, which include
   bounds checking.
2. Did not sufficiently check packet sizes.

Actually, 2) is mitigated but is still a problem, because the BFD header
is 2 bytes larger than the "normal" ZAPI header, while the overall
message size remains the same. So if the source message being duplicated
is actually right up against the ZAPI_MAX_PACKET_SIZ, you still can't
fit the whole message into your duplicated message. I have no idea what
the intent was here but at least there's a warning if it happens now.

Signed-off-by: Quentin Young <qlyoung@cumulusnetworks.com>
This commit is contained in:
Quentin Young 2020-01-03 21:18:49 -05:00
parent b833cc1ff4
commit ab12ca856c
1 changed files with 13 additions and 25 deletions
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38
zebra/zebra_ptm.c
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@ -1402,37 +1402,25 @@ static void _zebra_ptm_reroute(struct zserv *zs, struct zebra_vrf *zvrf,
struct stream *msg, uint32_t command)
{
struct stream *msgc;
size_t zmsglen, zhdrlen;
char buf[ZEBRA_MAX_PACKET_SIZ];
pid_t ppid;
/*
* Don't modify message in the zebra API. In order to do that we
* need to allocate a new message stream and copy the message
* provided by zebra.
*/
/* Create BFD header */
msgc = stream_new(ZEBRA_MAX_PACKET_SIZ);
if (msgc == NULL) {
zlog_debug("%s: not enough memory", __func__);
return;
}
/* Calculate our header size plus the message contents. */
zhdrlen = ZEBRA_HEADER_SIZE + sizeof(uint32_t);
zmsglen = msg->endp - msg->getp;
memcpy(msgc->data + zhdrlen, msg->data + msg->getp, zmsglen);
/*
* The message type will be BFD_DEST_REPLY so we can use only
* one callback at the `bfdd` side, however the real command
* number will be included right after the zebra header.
*/
zclient_create_header(msgc, ZEBRA_BFD_DEST_REPLAY, zvrf->vrf->vrf_id);
stream_putl(msgc, command);
/* Update the data pointers. */
msgc->getp = 0;
msgc->endp = zhdrlen + zmsglen;
stream_putw_at(msgc, 0, stream_get_endp(msgc));
if (STREAM_READABLE(msg) > STREAM_WRITEABLE(msgc)) {
zlog_warn("Cannot fit extended BFD header plus original message contents into ZAPI packet; dropping message");
goto stream_failure;
}
/* Copy original message, excluding header, into new message */
stream_get_from(buf, msg, stream_get_getp(msg), STREAM_READABLE(msg));
stream_put(msgc, buf, STREAM_READABLE(msg));
/* Update length field */
stream_putw_at(msgc, 0, STREAM_READABLE(msgc));
zebra_ptm_send_bfdd(msgc);