From 7a29f6bf60f2590fe5e9c4decb451e19afad2bcf Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 15 Jan 2026 09:21:39 +0000 Subject: [PATCH] l2tp: avoid one data-race in l2tp_tunnel_del_work() We should read sk->sk_socket only when dealing with kernel sockets. syzbot reported the following data-race: BUG: KCSAN: data-race in l2tp_tunnel_del_work / sk_common_release write to 0xffff88811c182b20 of 8 bytes by task 5365 on cpu 0: sk_set_socket include/net/sock.h:2092 [inline] sock_orphan include/net/sock.h:2118 [inline] sk_common_release+0xae/0x230 net/core/sock.c:4003 udp_lib_close+0x15/0x20 include/net/udp.h:325 inet_release+0xce/0xf0 net/ipv4/af_inet.c:437 __sock_release net/socket.c:662 [inline] sock_close+0x6b/0x150 net/socket.c:1455 __fput+0x29b/0x650 fs/file_table.c:468 ____fput+0x1c/0x30 fs/file_table.c:496 task_work_run+0x131/0x1a0 kernel/task_work.c:233 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] __exit_to_user_mode_loop kernel/entry/common.c:44 [inline] exit_to_user_mode_loop+0x1fe/0x740 kernel/entry/common.c:75 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline] syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline] syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline] do_syscall_64+0x1e1/0x2b0 arch/x86/entry/syscall_64.c:100 entry_SYSCALL_64_after_hwframe+0x77/0x7f read to 0xffff88811c182b20 of 8 bytes by task 827 on cpu 1: l2tp_tunnel_del_work+0x2f/0x1a0 net/l2tp/l2tp_core.c:1418 process_one_work kernel/workqueue.c:3257 [inline] process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3340 worker_thread+0x582/0x770 kernel/workqueue.c:3421 kthread+0x489/0x510 kernel/kthread.c:463 ret_from_fork+0x149/0x290 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246 value changed: 0xffff88811b818000 -> 0x0000000000000000 Fixes: d00fa9adc528 ("l2tp: fix races with tunnel socket close") Reported-by: syzbot+7312e82745f7fa2526db@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/6968b029.050a0220.58bed.0016.GAE@google.com/T/#u Signed-off-by: Eric Dumazet Cc: James Chapman Reviewed-by: Guillaume Nault Link: https://patch.msgid.link/20260115092139.3066180-1-edumazet@google.com Signed-off-by: Jakub Kicinski --- net/l2tp/l2tp_core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index 70335667ef03..f9b0f666600f 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -1416,8 +1416,6 @@ static void l2tp_tunnel_del_work(struct work_struct *work) { struct l2tp_tunnel *tunnel = container_of(work, struct l2tp_tunnel, del_work); - struct sock *sk = tunnel->sock; - struct socket *sock = sk->sk_socket; l2tp_tunnel_closeall(tunnel); @@ -1425,6 +1423,8 @@ static void l2tp_tunnel_del_work(struct work_struct *work) * the sk API to release it here. */ if (tunnel->fd < 0) { + struct socket *sock = tunnel->sock->sk_socket; + if (sock) { kernel_sock_shutdown(sock, SHUT_RDWR); sock_release(sock); -- 2.47.3