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res_rtp_asterisk: Fix dtls timer issues causing FRACKs and SEGVs

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In dtls_srtp_handle_timeout(), when DTLSv1_get_timeout() returned
success but with a timeout of 0, we were stopping the timer and
decrementing the refcount on instance but not resetting the
timeout_timer to -1.  When dtls_srtp_stop_timeout_timer()
was later called, it was atempting to stop a stale timer and could
decrement the refcount on instance again which would then cause
the instance destructor to run early.  This would result in either
a FRACK or a SEGV when ast_rtp_stop(0 was called.

According to the OpenSSL docs, we shouldn't have been stopping the
timer when DTLSv1_get_timeout() returned success and the new timeout
was 0 anyway.  We should have been calling DTLSv1_handle_timeout()
again immediately so we now reschedule the timer callback for
1ms (almost immediately).

Additionally, instead of scheduling the timer callback at a fixed
interval returned by the initial call to DTLSv1_get_timeout()
(usually 999 ms), we now reschedule the next callback based on
the last call to DTLSv1_get_timeout().

Resolves: #487
This commit is contained in:
George Joseph
2024-09-16 15:17:28 -06:00
parent ee9a0f056e
commit fe5bea34ab
1 changed files with 90 additions and 29 deletions
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119
res/res_rtp_asterisk.c
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@@ -2861,76 +2861,137 @@ static inline int rtcp_debug_test_addr(struct ast_sockaddr *addr)
}
#if defined(HAVE_OPENSSL) && (OPENSSL_VERSION_NUMBER >= 0x10001000L) && !defined(OPENSSL_NO_SRTP)
/*! \pre instance is locked */
static int dtls_srtp_handle_timeout(struct ast_rtp_instance *instance, int rtcp)
/*!
* \brief Handles DTLS timer expiration
*
* \param instance
* \param timeout
* \param rtcp
*
* If DTLSv1_get_timeout() returns 0, it's an error or no timeout was set.
* We need to unref instance and stop the timer in this case. Otherwise,
* new timeout may be a number of milliseconds or 0. If it's 0, OpenSSL
* is telling us to call DTLSv1_handle_timeout() immediately so we'll set
* timeout to 1ms so we get rescheduled almost immediately.
*
* \retval 0 - success
* \retval -1 - failure
*/
static int dtls_srtp_handle_timeout(struct ast_rtp_instance *instance, int *timeout, int rtcp)
{
struct ast_rtp *rtp = ast_rtp_instance_get_data(instance);
struct dtls_details *dtls = !rtcp ? &rtp->dtls : &rtp->rtcp->dtls;
struct timeval dtls_timeout;
int res = 0;
ast_debug_dtls(3, "(%p) DTLS srtp - handle timeout - rtcp=%d\n", instance, rtcp);
DTLSv1_handle_timeout(dtls->ssl);
res = DTLSv1_handle_timeout(dtls->ssl);
ast_debug_dtls(3, "(%p) DTLS srtp - handle timeout - rtcp=%d result: %d\n", instance, rtcp, res);
/* If a timeout can't be retrieved then this recurring scheduled item must stop */
if (!DTLSv1_get_timeout(dtls->ssl, &dtls_timeout)) {
res = DTLSv1_get_timeout(dtls->ssl, &dtls_timeout);
if (!res) {
/* Make sure we don't try to stop the timer later if it's already been stopped */
dtls->timeout_timer = -1;
return 0;
ao2_ref(instance, -1);
*timeout = 0;
ast_debug_dtls(3, "(%p) DTLS srtp - handle timeout - rtcp=%d get timeout failure\n", instance, rtcp);
return -1;
}
*timeout = dtls_timeout.tv_sec * 1000 + dtls_timeout.tv_usec / 1000;
if (*timeout == 0) {
/*
* If DTLSv1_get_timeout() succeeded with a timeout of 0, OpenSSL
* is telling us to call DTLSv1_handle_timeout() again now HOWEVER...
* Do NOT be tempted to call DTLSv1_handle_timeout() and
* DTLSv1_get_timeout() in a loop while the timeout is 0. There is only
* 1 thread running the scheduler for all PJSIP related RTP instances
* so we don't want to delay here any more than necessary. It's also
* possible that an OpenSSL bug or change in behavior could cause
* DTLSv1_get_timeout() to return 0 forever. If that happens, we'll
* be stuck here and no other RTP instances will get serviced.
* This RTP instance is also locked while this callback runs so we
* don't want to delay other threads that may need to lock this
* RTP instance for their own purpose.
*
* Just set the timeout to 1ms and let the scheduler reschedule us
* as quickly as possible.
*/
*timeout = 1;
}
ast_debug_dtls(3, "(%p) DTLS srtp - handle timeout - rtcp=%d timeout=%d\n", instance, rtcp, *timeout);
return dtls_timeout.tv_sec * 1000 + dtls_timeout.tv_usec / 1000;
return 0;
}
/* Scheduler callback */
static int dtls_srtp_handle_rtp_timeout(const void *data)
{
struct ast_rtp_instance *instance = (struct ast_rtp_instance *)data;
int reschedule;
int timeout = 0;
int res = 0;
ao2_lock(instance);
reschedule = dtls_srtp_handle_timeout(instance, 0);
res = dtls_srtp_handle_timeout(instance, &timeout, 0);
ao2_unlock(instance);
if (!reschedule) {
ao2_ref(instance, -1);
if (res < 0) {
/* Tells the scheduler to stop rescheduling */
return 0;
}
return reschedule;
/* Reschedule based on the timeout value */
return timeout;
}
/* Scheduler callback */
static int dtls_srtp_handle_rtcp_timeout(const void *data)
{
struct ast_rtp_instance *instance = (struct ast_rtp_instance *)data;
int reschedule;
int timeout = 0;
int res = 0;
ao2_lock(instance);
reschedule = dtls_srtp_handle_timeout(instance, 1);
res = dtls_srtp_handle_timeout(instance, &timeout, 1);
ao2_unlock(instance);
if (!reschedule) {
ao2_ref(instance, -1);
if (res < 0) {
/* Tells the scheduler to stop rescheduling */
return 0;
}
return reschedule;
/* Reschedule based on the timeout value */
return timeout;
}
static void dtls_srtp_start_timeout_timer(struct ast_rtp_instance *instance, struct ast_rtp *rtp, int rtcp)
{
struct dtls_details *dtls = !rtcp ? &rtp->dtls : &rtp->rtcp->dtls;
ast_sched_cb cb = !rtcp ? dtls_srtp_handle_rtp_timeout : dtls_srtp_handle_rtcp_timeout;
struct timeval dtls_timeout;
int res = 0;
int timeout = 0;
if (DTLSv1_get_timeout(dtls->ssl, &dtls_timeout)) {
int timeout = dtls_timeout.tv_sec * 1000 + dtls_timeout.tv_usec / 1000;
ast_assert(dtls->timeout_timer == -1);
ast_assert(dtls->timeout_timer == -1);
res = DTLSv1_get_timeout(dtls->ssl, &dtls_timeout);
if (res == 0) {
ast_debug_dtls(3, "(%p) DTLS srtp - DTLSv1_get_timeout return an error or there was no timeout set for %s\n",
instance, rtcp ? "RTCP" : "RTP");
return;
}
ao2_ref(instance, +1);
if ((dtls->timeout_timer = ast_sched_add(rtp->sched, timeout,
!rtcp ? dtls_srtp_handle_rtp_timeout : dtls_srtp_handle_rtcp_timeout, instance)) < 0) {
ao2_ref(instance, -1);
ast_log(LOG_WARNING, "Scheduling '%s' DTLS retransmission for RTP instance [%p] failed.\n",
!rtcp ? "RTP" : "RTCP", instance);
} else {
ast_debug_dtls(3, "(%p) DTLS srtp - scheduled timeout timer for '%d'\n", instance, timeout);
}
timeout = dtls_timeout.tv_sec * 1000 + dtls_timeout.tv_usec / 1000;
ao2_ref(instance, +1);
/*
* We want the timer to fire again based on calling DTLSv1_get_timeout()
* inside the callback, not at a fixed interval.
*/
if ((dtls->timeout_timer = ast_sched_add_variable(rtp->sched, timeout, cb, instance, 1)) < 0) {
ao2_ref(instance, -1);
ast_log(LOG_WARNING, "Scheduling '%s' DTLS retransmission for RTP instance [%p] failed.\n",
!rtcp ? "RTP" : "RTCP", instance);
} else {
ast_debug_dtls(3, "(%p) DTLS srtp - scheduled timeout timer for '%d' %s\n",
instance, timeout, rtcp ? "RTCP" : "RTP");
}
}