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Hi all,
When upgrading to v2024.11.28, multicast streams with SRTP sometimes fail due
to an uninitialized variable; Clients are not able to decode SRTP and discard
all packets.
Short: SRTPCryptographicContext constructor does not initialize fSendingROC.
Long:
PassiveServerMediaSubsession::sdpLines() is called from
ServerMediaSession::generateSDPDescription() twice.
The first time (to determine existence), the cryptographic context of the sink
of PassiveServerMediaSubsession is NULL, so the RTPSink::srtpROC() returns 0;
However, PassiveServerMediaSubsession::sdpLines() then performs a
fRTPSink.setupForSRTP(), which initializes the cryptographic context. At this
point, the fSendingROC member is uninitialized.
ServerMediaSession::generateSDPDescription() then calls
PassiveServerMediaSubsession::sdpLines() a second time (to actually fill SDP),
and then references this cryptographic context. Uninitialized memory is
returned, letting PassiveServerMediaSubsession::sdpLines() to re-create
SDPLines with a bogus ROC.
Only later, when RTP is to be sent,
SRTPCryptographicContext::processOutgoingSRTPPacket() initializes fSendingROC
for the first call.
Proposed solutions:
a) SRTPCryptographicContext::sendingROC() should return
fMIKEYState.initialROC() if nothing was sent yet (simpler, but introduces
duplication)
b) constructor should initialize fSendingROC with fMIKEYState.initialROC() -
which would also allow for the removal of the initialization in
processOutgoingSRTPPacket().
Note: The IDE (CLion) also warns about further, uninitialized members in
SRTPCryptographicContext - though I haven't followed up on their implications.
Thank you,
Christian
Christian Haas
OneATM - Tower Solutions R&D - Software Engineer
FREQUENTIS AG
Innovationsstrasse 1
1100 Vienna, Austria
Mobile: +43-664-60 850 - 3471
Fax: +43-1-811 50 - 77 - 3471
Web: www.frequentis.com<http://www.frequentis.com/>
E-mail: christian.h...@frequentis.com<mailto:christian.h...@frequentis.com>
Handelsgericht Wien (Vienna Commercial Court): FN 72115b
ATU 14715600
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