CVE-2026-74628net/x25: fix use-after-free of the socket by its timers

Official description

In the Linux kernel, the following vulnerability has been resolved: net/x25: fix use-after-free of the socket by its timers The x25 timers are armed with mod_timer() and cancelled with timer_delete(), so a pending timer holds no reference on the socket and a cancel does not wait for a callback already running on another CPU. x25_heartbeat_expiry() also rearms unconditionally, so it can reinstall sk->sk_timer after __x25_destroy_socket() has passed its cancel point. The following __sock_put() frees the socket while the timer is still queued, and the next expiry uses freed memory. KASAN reports a slab-use-after-free on the kmalloc-2k object freed by close(). timer_delete_sync() cannot be used here: x25_heartbeat_expiry() and x25_timer_expiry() both reach the cancels from inside the timer they would wait on, through __x25_destroy_socket() and x25_disconnect(). Arm the timers with sk_reset_timer() and cancel them with sk_stop_timer() so that an armed timer owns a reference, and release it in both expiry handlers. Rearm the heartbeat only while sk_hashed(sk) is still true, since __x25_destroy_socket() unlinks the socket before dropping it. Arm the deferred destroy timer the same way and drop its reference in x25_destroy_timer(). Reproduced on net with KASAN, with the heartbeat period shortened so the window recurs. With this patch the reproducer no longer triggers a report and /proc/net/x25 drains. Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/ba925a2e98ce967a0e71c5bcbcf5dbd3facaf0c8
• https://git.kernel.org/stable/c/6b79659590f0f82a9b8efd2ffd55ec6399ebfc33
• https://git.kernel.org/stable/c/fdd9ac50b9b61ef2b2d52c5156aff788be91454d
• https://git.kernel.org/stable/c/1fc9f6d2c7c9fdb341bfe8ca449c990632299ea6
• https://git.kernel.org/stable/c/3c4919be5d910db4beebca420953858606fba7d8
• https://git.kernel.org/stable/c/4bc522b33438fefc3272840ae5988771863a4f1f
• https://git.kernel.org/stable/c/e92c7e2b41d1528a830bc64c5e4e46dfa8133dda
• https://git.kernel.org/stable/c/2195424c3da2ef1829a63b807e3a900a90e57d85