CVE-2026-46227

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

sctp: revalidate list cursor after sctp_sendmsg_to_asoc() in SCTP_SENDALL

The SCTP_SENDALL path in sctp_sendmsg() iterates ep->asocs with

list_for_each_entry_safe(), which caches the next entry in @tmp before

the loop body runs. The body calls sctp_sendmsg_to_asoc(), which may

drop the socket lock inside sctp_wait_for_sndbuf().

While the lock is dropped, another thread can SCTP_SOCKOPT_PEELOFF the

association cached in @tmp, migrating it to a new endpoint via

sctp_sock_migrate() (list_del_init() + list_add_tail() to

newep->asocs), and optionally close the new socket which frees the

association via kfree_rcu(). The cached @tmp can also be freed by a

network ABORT for that association, processed in softirq while the

lock is dropped.

sctp_wait_for_sndbuf() revalidates @asoc (the current entry) on re-lock

via the "sk != asoc->base.sk" and "asoc->base.dead" checks, but nothing

revalidates @tmp. After a successful return, the iterator advances to

the stale @tmp, yielding either a use-after-free (if the peeled socket

was closed) or a list-walk onto the new endpoint's list head (type

confusion of &newep->asocs as a struct sctp_association *).

Both are reachable from CapEff=0; the type-confusion path gives

controlled indirect call via the outqueue.sched->init_sid pointer.

Fix by re-deriving @tmp from @asoc after sctp_sendmsg_to_asoc()

returns. @asoc is known to still be on ep->asocs at that point: the

only callers that list_del an association from ep->asocs are

sctp_association_free() (which sets asoc->base.dead) and

sctp_assoc_migrate() (which changes asoc->base.sk), and

sctp_wait_for_sndbuf() checks both under the lock before any

successful return; a tripped check propagates as err < 0 and the loop

bails before the re-derive.

The SCTP_ABORT path in sctp_sendmsg_check_sflags() returns 0 and the

loop hits 'continue' before sctp_sendmsg_to_asoc() is ever called, so

the @tmp cached by list_for_each_entry_safe() still covers the

lock-held free that ba59fb027307 ("sctp: walk the list of asoc

safely") was added for.