CVE-2026-98846: sctp: check RCV_SHUTDOWN after the sendmsg connect wait

CVE-2026-98846: sctp: check RCV_SHUTDOWN after the sendmsg connect wait

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

sctp: check RCV_SHUTDOWN after the sendmsg connect wait

sctp_wait_for_connect() drops the socket lock while it sleeps. An
out-of-the-blue ABORT can then be processed from the socket backlog and
unlink the association. If a concurrent shutdown(fd, SHUT_RD) sets
RCV_SHUTDOWN, the waiter breaks with err == 0 before checking
asoc->base.dead. Its final sctp_association_put() can then free the
association, leaving sctp_sendmsg_to_asoc() to continue with a dangling
pointer.

Check RCV_SHUTDOWN along with the wait error in sctp_sendmsg_to_asoc()
before using the association again. The check only accesses the socket,
so it needs no additional association reference. Return the existing
-ESRCH so that sctp_sendmsg() skips freeing a new association that may
already have been destroyed.

Keep sctp_wait_for_connect() unchanged to preserve its behavior for the
connect() caller.

The Linux kernel CVE team has assigned CVE-2026-98846 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 4.16 with commit 668c9beb9020d5834ee9e43c208190a07d2b1928 and fixed in 6.12.113 with commit e8f972b1759d26bbefe4c524caae1ed7c8a593bd
	Issue introduced in 4.16 with commit 668c9beb9020d5834ee9e43c208190a07d2b1928 and fixed in 6.18.56 with commit e701345d886e831fb593a0870d69c8c5de6fc938
	Issue introduced in 4.16 with commit 668c9beb9020d5834ee9e43c208190a07d2b1928 and fixed in 7.2.10 with commit 222c41e0f50f1d5028be9baf0e1dcfc0bfa7f669
	Issue introduced in 4.16 with commit 668c9beb9020d5834ee9e43c208190a07d2b1928 and fixed in 7.3-rc6 with commit 4f1da630d13de0370e2f6361f961f1c8b384af1c

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-98846
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/sctp/socket.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/e8f972b1759d26bbefe4c524caae1ed7c8a593bd
	https://git.kernel.org/stable/c/e701345d886e831fb593a0870d69c8c5de6fc938
	https://git.kernel.org/stable/c/222c41e0f50f1d5028be9baf0e1dcfc0bfa7f669
	https://git.kernel.org/stable/c/4f1da630d13de0370e2f6361f961f1c8b384af1c