CVE-2024-26731

In the Linux kernel, the following vulnerability has been resolved: bpf,
sockmap: Fix NULL pointer dereference in sk_psock_verdict_data_ready()
syzbot reported the following NULL pointer dereference issue [1]: BUG:
kernel NULL pointer dereference, address: 0000000000000000 […] RIP:
0010:0x0 […] Call Trace: <TASK> sk_psock_verdict_data_ready+0x232/0x340
net/core/skmsg.c:1230 unix_stream_sendmsg+0x9b4/0x1230
net/unix/af_unix.c:2293 sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg+0x221/0x270 net/socket.c:745 ____sys_sendmsg+0x525/0x7d0
net/socket.c:2584 ___sys_sendmsg net/socket.c:2638 [inline]
__sys_sendmsg+0x2b0/0x3a0 net/socket.c:2667 do_syscall_64+0xf9/0x240
entry_SYSCALL_64_after_hwframe+0x6f/0x77 If sk_psock_verdict_data_ready()
and sk_psock_stop_verdict() are called concurrently,
psock->saved_data_ready can be NULL, causing the above issue. This patch
fixes this issue by calling the appropriate data ready function using the
sk_psock_data_ready() helper and protecting it from concurrency with
sk->sk_callback_lock.