kcm: annotate data-races around kcm->rx_wait

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

kcm: annotate data-races around kcm->rx_wait

kcm->rx_psock can be read locklessly in kcm_rfree().

Annotate the read and writes accordingly.

syzbot reported:

BUG: KCSAN: data-race in kcm_rcv_strparser / kcm_rfree

write to 0xffff88810784e3d0 of 1 bytes by task 1823 on cpu 1:

reserve_rx_kcm net/kcm/kcmsock.c:283 [inline]

kcm_rcv_strparser+0x250/0x3a0 net/kcm/kcmsock.c:363

__strp_recv+0x64c/0xd20 net/strparser/strparser.c:301

strp_recv+0x6d/0x80 net/strparser/strparser.c:335

tcp_read_sock+0x13e/0x5a0 net/ipv4/tcp.c:1703

strp_read_sock net/strparser/strparser.c:358 [inline]

do_strp_work net/strparser/strparser.c:406 [inline]

strp_work+0xe8/0x180 net/strparser/strparser.c:415

process_one_work+0x3d3/0x720 kernel/workqueue.c:2289

worker_thread+0x618/0xa70 kernel/workqueue.c:2436

kthread+0x1a9/0x1e0 kernel/kthread.c:376

ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306

read to 0xffff88810784e3d0 of 1 bytes by task 17869 on cpu 0:

kcm_rfree+0x121/0x220 net/kcm/kcmsock.c:181

skb_release_head_state+0x8e/0x160 net/core/skbuff.c:841

skb_release_all net/core/skbuff.c:852 [inline]

__kfree_skb net/core/skbuff.c:868 [inline]

kfree_skb_reason+0x5c/0x260 net/core/skbuff.c:891

kfree_skb include/linux/skbuff.h:1216 [inline]

kcm_recvmsg+0x226/0x2b0 net/kcm/kcmsock.c:1161

____sys_recvmsg+0x16c/0x2e0

___sys_recvmsg net/socket.c:2743 [inline]

do_recvmmsg+0x2f1/0x710 net/socket.c:2837

__sys_recvmmsg net/socket.c:2916 [inline]

__do_sys_recvmmsg net/socket.c:2939 [inline]

__se_sys_recvmmsg net/socket.c:2932 [inline]

__x64_sys_recvmmsg+0xde/0x160 net/socket.c:2932

do_syscall_x64 arch/x86/entry/common.c:50 [inline]

do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80

entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x01 -> 0x00

Reported by Kernel Concurrency Sanitizer on:

CPU: 0 PID: 17869 Comm: syz-executor.2 Not tainted 6.1.0-rc1-syzkaller-00010-gbb1a1146467a-dirty #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/22/2022