From 7b393b81f9aef803cd8d2fbb0f1cc9d2b821db12 Mon Sep 17 00:00:00 2001 From: Baul Lee Date: Mon, 27 Jul 2026 07:03:42 +0900 Subject: [PATCH] net/x25: fix use-after-free of the socket by its timers ANBZ: #44450 commit 2195424c3da2ef1829a63b807e3a900a90e57d85 upstream. 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 [backport-note] PatchPilot-Conflict-Type: context_drift PatchPilot-Conflict-Files: net/x25/x25_timer.c PatchPilot-Resolution: net/x25/x25_timer.c: Replace del_timer() with sk_stop_timer() in x25_stop_heartbeat and... Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Baul Lee Link: https://patch.msgid.link/20260726220342.47245-1-baul.lee@xbow.com Signed-off-by: Jakub Kicinski Fixes: CVE-2026-74628 Assisted-by: PatchPilot Signed-off-by: D. Wythe --- net/x25/af_x25.c | 4 ++-- net/x25/x25_timer.c | 27 +++++++++++++++++---------- 2 files changed, 19 insertions(+), 12 deletions(-) diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c index f15a4493eb0b..2e967148ec5e 100644 --- a/net/x25/af_x25.c +++ b/net/x25/af_x25.c @@ -362,6 +362,7 @@ static void x25_destroy_timer(struct timer_list *t) struct sock *sk = from_timer(sk, t, sk_timer); x25_destroy_socket_from_timer(sk); + sock_put(sk); } /* @@ -397,9 +398,8 @@ static void __x25_destroy_socket(struct sock *sk) if (sk_has_allocations(sk)) { /* Defer: outstanding buffers */ - sk->sk_timer.expires = jiffies + 10 * HZ; sk->sk_timer.function = x25_destroy_timer; - add_timer(&sk->sk_timer); + sk_reset_timer(sk, &sk->sk_timer, jiffies + 10 * HZ); } else { /* drop last reference so sock_put will free */ __sock_put(sk); diff --git a/net/x25/x25_timer.c b/net/x25/x25_timer.c index 9376365cdcc9..4e6916c7c83a 100644 --- a/net/x25/x25_timer.c +++ b/net/x25/x25_timer.c @@ -11,7 +11,7 @@ * History * X.25 001 Jonathan Naylor Started coding. * X.25 002 Jonathan Naylor New timer architecture. - * Centralised disconnection processing. + * Centralised disconnection processing. */ #include @@ -36,45 +36,45 @@ void x25_init_timers(struct sock *sk) void x25_start_heartbeat(struct sock *sk) { - mod_timer(&sk->sk_timer, jiffies + 5 * HZ); + sk_reset_timer(sk, &sk->sk_timer, jiffies + 5 * HZ); } void x25_stop_heartbeat(struct sock *sk) { - del_timer(&sk->sk_timer); + sk_stop_timer(sk, &sk->sk_timer); } void x25_start_t2timer(struct sock *sk) { struct x25_sock *x25 = x25_sk(sk); - mod_timer(&x25->timer, jiffies + x25->t2); + sk_reset_timer(sk, &x25->timer, jiffies + x25->t2); } void x25_start_t21timer(struct sock *sk) { struct x25_sock *x25 = x25_sk(sk); - mod_timer(&x25->timer, jiffies + x25->t21); + sk_reset_timer(sk, &x25->timer, jiffies + x25->t21); } void x25_start_t22timer(struct sock *sk) { struct x25_sock *x25 = x25_sk(sk); - mod_timer(&x25->timer, jiffies + x25->t22); + sk_reset_timer(sk, &x25->timer, jiffies + x25->t22); } void x25_start_t23timer(struct sock *sk) { struct x25_sock *x25 = x25_sk(sk); - mod_timer(&x25->timer, jiffies + x25->t23); + sk_reset_timer(sk, &x25->timer, jiffies + x25->t23); } void x25_stop_timer(struct sock *sk) { - del_timer(&x25_sk(sk)->timer); + sk_stop_timer(sk, &x25_sk(sk)->timer); } unsigned long x25_display_timer(struct sock *sk) @@ -108,7 +108,7 @@ static void x25_heartbeat_expiry(struct timer_list *t) sock_flag(sk, SOCK_DEAD))) { bh_unlock_sock(sk); x25_destroy_socket_from_timer(sk); - return; + goto out; } break; @@ -120,8 +120,14 @@ static void x25_heartbeat_expiry(struct timer_list *t) break; } restart_heartbeat: - x25_start_heartbeat(sk); + /* Do not rearm once __x25_destroy_socket() has unlinked the socket: + * it is past its cancel point and owns the teardown from there on. + */ + if (sk_hashed(sk)) + x25_start_heartbeat(sk); bh_unlock_sock(sk); +out: + sock_put(sk); } /* @@ -166,4 +172,5 @@ static void x25_timer_expiry(struct timer_list *t) } else x25_do_timer_expiry(sk); bh_unlock_sock(sk); + sock_put(sk); } -- Gitee