socket: Add osmo_sock_init flag to enable SCTP ASCONF features
The SCTP_ASCONF_SUPPORTED sockopt, which enables ASCONF features
for the SCTP associations managed by the SCTP socket, gets its default
value from to sysctl "net.sctp.addip_enable", which, at least up to
current kernel 6.4.8 is set to "0" (disabled) by default.
As a result, ASCONF related features such as
setsockopt(SCTP_SET_PEER_PRIMARY_ADDR) fail with -EPERM
since ASNCONF extensions where not negotiated during the SCTP init
handshake.
This commit adds support for setting SCTP_ASCONF_SUPPORTED=1 during
socket creation, since that needs to be applied before the first
bind()/connect() (before first assoc is created).
Furthermore, for ASCONF features to work properly, the assoc also needs
to announce/use the AUTH extension, as per RFC5061 section 4.2.7.
Otherwise, the peer receiving an SCTP INIT with
ExtensionFeatures=ASCONF,ASCONF_ACK but without AUTH, will reject the
assoc with an ABORT since it's not complying with spec (this behavior
can be tweaked through sysctl "net.sctp.addip_noauth_enable").
The AUTH extension is enabled through sockopt SCTP_AUTH_SUPPORTED, and
its default value is that of sysctl "net.sctp.auth_enable", which is
also disabled (0) by default.
Kernel support for those is relatively new:
SCTP_FUTURE_ASSOC added in: 80df2704a375bb4b3c9c5cce9c00052361b16d61
Follows: v5.0-rc4
Precedes: v5.1-rc1
SCTP_ASCONF_SUPPORTED added in: df2c71ffdfae58961981d7cbcccea93688fc4e96
Follows: v5.3-rc5
Precedes: v5.4-rc1
SCTP_AUTH_SUPPORTED added in: 56dd525abd56f7acd7b44a52935726e3ada4916c
Follows: v5.3-rc5
Precedes: v5.4-rc1
Related: OS#6076
Change-Id: Iac07031927b66a9d32d2bb2faab817e4c922a359
diff --git a/include/osmocom/core/socket.h b/include/osmocom/core/socket.h
index 6bac87d..c68bb6f 100644
--- a/include/osmocom/core/socket.h
+++ b/include/osmocom/core/socket.h
@@ -94,6 +94,8 @@
#define OSMO_SOCK_F_NO_MCAST_ALL (1 << 4)
/*! use SO_REUSEADDR on UDP ports (required for multicast) */
#define OSMO_SOCK_F_UDP_REUSEADDR (1 << 5)
+/*! use SCTP_AUTH_SUPPORTED + SCTP_ASCONF_SUPPORTED on SCTP socket (required for ASCONF / Peer Primary Address feature) */
+#define OSMO_SOCK_F_SCTP_ASCONF_SUPPORTED (1 << 6)
/*! use OSMO_SOCK_F_DSCP(x) to set IP DSCP 'x' for packets transmitted on the socket */
#define OSMO_SOCK_F_DSCP(x) (((x)&0x3f) << 24)