CVE-2021-46999

In the Linux kernel, the following vulnerability has been resolved:

sctp: do asoc update earlier in sctp_sf_do_dupcook_a

There's a panic that occurs in a few of envs, the call trace is as below:

[] general protection fault, ... 0x29acd70f1000a: 0000 [#1] SMP PTI

[] RIP: 0010:sctp_ulpevent_notify_peer_addr_change+0x4b/0x1fa [sctp]

[] sctp_assoc_control_transport+0x1b9/0x210 [sctp]

[] sctp_do_8_2_transport_strike.isra.16+0x15c/0x220 [sctp]

[] sctp_cmd_interpreter.isra.21+0x1231/0x1a10 [sctp]

[] sctp_do_sm+0xc3/0x2a0 [sctp]

[] sctp_generate_timeout_event+0x81/0xf0 [sctp]

This is caused by a transport use-after-free issue. When processing a

duplicate COOKIE-ECHO chunk in sctp_sf_do_dupcook_a(), both COOKIE-ACK

and SHUTDOWN chunks are allocated with the transort from the new asoc.

However, later in the sideeffect machine, the old asoc is used to send

them out and old asoc's shutdown_last_sent_to is set to the transport

that SHUTDOWN chunk attached to in sctp_cmd_setup_t2(), which actually

belongs to the new asoc. After the new_asoc is freed and the old asoc

T2 timeout, the old asoc's shutdown_last_sent_to that is already freed

would be accessed in sctp_sf_t2_timer_expire().

Thanks Alexander and Jere for helping dig into this issue.

To fix it, this patch is to do the asoc update first, then allocate

the COOKIE-ACK and SHUTDOWN chunks with the 'updated' old asoc. This

would make more sense, as a chunk from an asoc shouldn't be sent out

with another asoc. We had fixed quite a few issues caused by this.