> -----Original Message----- > From: Jakub Sitnicki [mailto:jakub@xxxxxxxxxxxxxx] > Sent: Friday, August 19, 2022 4:39 PM > To: liujian (CE) <liujian56@xxxxxxxxxx>; john.fastabend@xxxxxxxxx; > edumazet@xxxxxxxxxx > Cc: davem@xxxxxxxxxxxxx; yoshfuji@xxxxxxxxxxxxxx; dsahern@xxxxxxxxxx; > kuba@xxxxxxxxxx; pabeni@xxxxxxxxxx; andrii@xxxxxxxxxx; mykolal@xxxxxx; > ast@xxxxxxxxxx; daniel@xxxxxxxxxxxxx; martin.lau@xxxxxxxxx; > song@xxxxxxxxxx; yhs@xxxxxx; kpsingh@xxxxxxxxxx; sdf@xxxxxxxxxx; > haoluo@xxxxxxxxxx; jolsa@xxxxxxxxxx; shuah@xxxxxxxxxx; > bpf@xxxxxxxxxxxxxxx > Subject: Re: [PATCH bpf-next 1/2] sk_msg: Keep reference on socket file > while wait_memory > > On Mon, Aug 15, 2022 at 10:33 AM +08, Liu Jian wrote: > > Fix the below NULL pointer dereference: > > > > [ 14.471200] Call Trace: > > [ 14.471562] <TASK> > > [ 14.471882] lock_acquire+0x245/0x2e0 > > [ 14.472416] ? remove_wait_queue+0x12/0x50 > > [ 14.473014] ? _raw_spin_lock_irqsave+0x17/0x50 > > [ 14.473681] _raw_spin_lock_irqsave+0x3d/0x50 > > [ 14.474318] ? remove_wait_queue+0x12/0x50 > > [ 14.474907] remove_wait_queue+0x12/0x50 > > [ 14.475480] sk_stream_wait_memory+0x20d/0x340 > > [ 14.476127] ? do_wait_intr_irq+0x80/0x80 > > [ 14.476704] do_tcp_sendpages+0x287/0x600 > > [ 14.477283] tcp_bpf_push+0xab/0x260 > > [ 14.477817] tcp_bpf_sendmsg_redir+0x297/0x500 > > [ 14.478461] ? __local_bh_enable_ip+0x77/0xe0 > > [ 14.479096] tcp_bpf_send_verdict+0x105/0x470 > > [ 14.479729] tcp_bpf_sendmsg+0x318/0x4f0 > > [ 14.480311] sock_sendmsg+0x2d/0x40 > > [ 14.480822] ____sys_sendmsg+0x1b4/0x1c0 > > [ 14.481390] ? copy_msghdr_from_user+0x62/0x80 > > [ 14.482048] ___sys_sendmsg+0x78/0xb0 > > [ 14.482580] ? vmf_insert_pfn_prot+0x91/0x150 > > [ 14.483215] ? __do_fault+0x2a/0x1a0 > > [ 14.483738] ? do_fault+0x15e/0x5d0 > > [ 14.484246] ? __handle_mm_fault+0x56b/0x1040 > > [ 14.484874] ? lock_is_held_type+0xdf/0x130 > > [ 14.485474] ? find_held_lock+0x2d/0x90 > > [ 14.486046] ? __sys_sendmsg+0x41/0x70 > > [ 14.486587] __sys_sendmsg+0x41/0x70 > > [ 14.487105] ? intel_pmu_drain_pebs_core+0x350/0x350 > > [ 14.487822] do_syscall_64+0x34/0x80 > > [ 14.488345] entry_SYSCALL_64_after_hwframe+0x63/0xcd > > > > The test scene as following flow: > > thread1 thread2 > > ----------- --------------- > > tcp_bpf_sendmsg > > tcp_bpf_send_verdict > > tcp_bpf_sendmsg_redir sock_close > > tcp_bpf_push_locked __sock_release > > tcp_bpf_push //inet_release > > do_tcp_sendpages sock->ops->release > > sk_stream_wait_memory // tcp_close > > sk_wait_event sk->sk_prot->close > > release_sock(__sk); > > *** > > > > lock_sock(sk); > > __tcp_close > > sock_orphan(sk) > > sk->sk_wq = NULL > > release_sock > > **** > > lock_sock(__sk); > > remove_wait_queue(sk_sleep(sk), &wait); > > sk_sleep(sk) > > //NULL pointer dereference > > &rcu_dereference_raw(sk->sk_wq)->wait > > > > While waiting for memory in thread1, the socket is released with its > > wait queue because thread2 has closed it. This caused by > > tcp_bpf_send_verdict didn't increase the f_count of psock->sk_redir- > >sk_socket->file in thread1. > > I'm not sure about this approach. Keeping a closed sock file alive, just so we > can wakeup from sleep, seems like wasted effort. > > __tcp_close sets sk->sk_shutdown = RCV_SHUTDOWN | SEND_SHUTDOWN. > So we will return from sk_stream_wait_memory via the do_error path. > > SEND_SHUTDOWN might be set because socket got closed and orphaned - > dead and detached from its file, like in this case. > > So, IMHO, we should check if SOCK_DEAD flag is set on wakeup due to > SEND_SHUTDOWN in sk_stream_wait_memory, before accessing the wait > queue. > > [...] As jakub's approach, this problem can be solved. diff --git a/include/net/sock.h b/include/net/sock.h index a7273b289188..a3dab7140f1e 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1998,6 +1998,8 @@ static inline void sk_set_socket(struct sock *sk, struct socket *sock) static inline wait_queue_head_t *sk_sleep(struct sock *sk) { BUILD_BUG_ON(offsetof(struct socket_wq, wait) != 0); + if (sock_flag(sk, SOCK_DEAD)) + return NULL; return &rcu_dereference_raw(sk->sk_wq)->wait; } /* Detach socket from process context. diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c index 9860bb9a847c..da1be17d0b19 100644 --- a/kernel/sched/wait.c +++ b/kernel/sched/wait.c @@ -51,6 +51,8 @@ void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry { unsigned long flags; + if (wq_head == NULL) + return; spin_lock_irqsave(&wq_head->lock, flags); __remove_wait_queue(wq_head, wq_entry); spin_unlock_irqrestore(&wq_head->lock, flags);
