CVE-2021-46999

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

sctp: do asoc update earlier in sctp_sf_do_dupcook_a

Theres 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 asocs 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 asocs 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 shouldnt be sent out with another asoc. We had fixed quite a few issues caused by this.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/0bfd913c2121b3d553bfd52810fe6061d542d625
• https://git.kernel.org/stable/c/35b4f24415c854cd718ccdf38dbea6297f010aae
• https://git.kernel.org/stable/c/61b877bad9bb0d82b7d8841be50872557090a704
• https://git.kernel.org/stable/c/b1b31948c0af44628e43353828453461bb74098f
• https://git.kernel.org/stable/c/d624f2991b977821375fbd56c91b0c91d456a697
• https://git.kernel.org/stable/c/f01988ecf3654f805282dce2d3bb9afe68d2691e
• https://git.kernel.org/stable/c/0bfd913c2121b3d553bfd52810fe6061d542d625
• https://git.kernel.org/stable/c/35b4f24415c854cd718ccdf38dbea6297f010aae
• https://git.kernel.org/stable/c/61b877bad9bb0d82b7d8841be50872557090a704
• https://git.kernel.org/stable/c/b1b31948c0af44628e43353828453461bb74098f
• https://git.kernel.org/stable/c/d624f2991b977821375fbd56c91b0c91d456a697
• https://git.kernel.org/stable/c/f01988ecf3654f805282dce2d3bb9afe68d2691e