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. [...]
