A P-CSCF may answer the challenge with every mechanism it supports and
attach the SPIs and ports to the one it applied. O2 UK's core lists six
ipsec-3gpp entries with q-values, md5 first, and marks the fourth (sha1,
no ealg). imsd took the first ealg= anywhere in the header - the 3DES of
an entry the P-CSCF had not selected - and installed SAs the far end
could not decrypt: every protected packet after the 401 was dropped at
its IPsec layer, over TCP and UDP alike, with nothing to answer.
The 401 handling now parses the Security-Server as a mechanism list
(commas outside quotes, parameters on semicolons, names and values
case-insensitive) and selects the highest-q ipsec-3gpp mechanism that
matches what Security-Client offered (RFC 3329 2.3.1, TS 24.229
5.1.1.5.1): alg equal to ours, ealg (absent = null) equal to the offer.
The SPIs and ports are per registration and come from the entry carrying
them. When no entry matches the offer, the entry carrying the SPIs is
installed as listed and the journal says so; hmac-md5-96 becomes
hmac(md5) with IK as the key. A single-mechanism header selects itself:
on KPN the SAs are the same as before (unit-pinned argv, verified on the
phone). An answer that cannot be used - no ipsec-3gpp entry, a missing
spi/port, an alg, ealg, prot or mod the kernel cannot be handed - defers
the bring-up on the throttle schedule with the reason, before the AKA is
spent, instead of a fatal that would restart imsd every RestartSec with
an initial REGISTER each time; spi-s=0 stays the throttle deferral.
Repeated Security-Server header lines are joined into the one list
Security-Verify echoes.
The journal shows the Security-Server line, the selected mechanism, the
SA parameters, and any ip xfrm command that fails (keys masked) at every
fresh registration - the silence this bug produced had no line to read.
Userspace VoLTE/IMS daemon for mainline Linux phones (developed on the
Fairphone 6): a GLib-free core (SIP, SDP, USIM AKA, IPsec SA setup, RTP
media, call engine) behind a GDBus control daemon, a standalone AMR-WB
media leg, and a Plasma Dialer backend. C++26 modules built with Crafter
Build; the tree is clean under the project's house-style linter
(crafter-build lint) across all three build products.
Assisted-by: Claude:claude-fable-5
Signed-off-by: Jorijn van der Graaf <jorijnvdgraaf@catcrafts.net>
