CVE-2026-68137

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

net/x25: fix use-after-free in x25killby_neigh()

x25killby_neigh() walks the global X.25 socket list looking for sockets

attached to a terminating neighbour. x25listlock protects list membership

while the lookup is in progress, but it does not pin a socket's lifetime

after the lock is dropped.

The function currently drops x25listlock before calling lock_sock(s). A

concurrent close can run x25_release(), remove the same socket from

x25_list, and drop the last socket reference in that window. The neighbour

teardown path can then lock or inspect a freed struct sock/struct x25_sock.

Take sockhold(s) while x25list_lock still proves that the list entry is

live, then drop the temporary reference after the socket has been locked,

rechecked, and released. Recheck x25sk(s)->neighbour after locksock(),

because another path may have disconnected the socket before this path

acquired the socket lock. Restart the list walk after each disconnect

because the list lock was dropped and the previous iterator state may no

longer be valid.

A QEMU/KASAN run against origin/master reproduced a slab-use-after-free in

x25killby_neigh().