net: If sock is dead don't access sock's sk_wq in sk_stream_wait_memory

In the Linux kernel, the following vulnerability has been resolved:

net: If sock is dead don't access sock's sk_wq in sk_stream_wait_memory

Fixes 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 scenario has the 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.

We should check if SOCK_DEAD flag is set on wakeup in sk_stream_wait_memory

before accessing the wait queue.