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

Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 0109ef6..63e32f1 100644 (file)
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -162,7 +162,8 @@ static void kcm_rcv_ready(struct kcm_sock *kcm)
        /* Buffer limit is okay now, add to ready list */
        list_add_tail(&kcm->wait_rx_list,
                      &kcm->mux->kcm_rx_waiters);
-       kcm->rx_wait = true;
+       /* paired with lockless reads in kcm_rfree() */
+       WRITE_ONCE(kcm->rx_wait, true);
 }
 
 static void kcm_rfree(struct sk_buff *skb)
@@ -178,7 +179,7 @@ static void kcm_rfree(struct sk_buff *skb)
        /* For reading rx_wait and rx_psock without holding lock */
        smp_mb__after_atomic();
 
-       if (!kcm->rx_wait && !READ_ONCE(kcm->rx_psock) &&
+       if (!READ_ONCE(kcm->rx_wait) && !READ_ONCE(kcm->rx_psock) &&
            sk_rmem_alloc_get(sk) < sk->sk_rcvlowat) {
                spin_lock_bh(&mux->rx_lock);
                kcm_rcv_ready(kcm);
@@ -237,7 +238,8 @@ try_again:
                if (kcm_queue_rcv_skb(&kcm->sk, skb)) {
                        /* Should mean socket buffer full */
                        list_del(&kcm->wait_rx_list);
-                       kcm->rx_wait = false;
+                       /* paired with lockless reads in kcm_rfree() */
+                       WRITE_ONCE(kcm->rx_wait, false);
 
                        /* Commit rx_wait to read in kcm_free */
                        smp_wmb();
@@ -280,7 +282,8 @@ static struct kcm_sock *reserve_rx_kcm(struct kcm_psock *psock,
        kcm = list_first_entry(&mux->kcm_rx_waiters,
                               struct kcm_sock, wait_rx_list);
        list_del(&kcm->wait_rx_list);
-       kcm->rx_wait = false;
+       /* paired with lockless reads in kcm_rfree() */
+       WRITE_ONCE(kcm->rx_wait, false);
 
        psock->rx_kcm = kcm;
        /* paired with lockless reads in kcm_rfree() */
@@ -1242,7 +1245,8 @@ static void kcm_recv_disable(struct kcm_sock *kcm)
        if (!kcm->rx_psock) {
                if (kcm->rx_wait) {
                        list_del(&kcm->wait_rx_list);
-                       kcm->rx_wait = false;
+                       /* paired with lockless reads in kcm_rfree() */
+                       WRITE_ONCE(kcm->rx_wait, false);
                }
 
                requeue_rx_msgs(mux, &kcm->sk.sk_receive_queue);
@@ -1795,7 +1799,8 @@ static void kcm_done(struct kcm_sock *kcm)
 
        if (kcm->rx_wait) {
                list_del(&kcm->wait_rx_list);
-               kcm->rx_wait = false;
+               /* paired with lockless reads in kcm_rfree() */
+               WRITE_ONCE(kcm->rx_wait, false);
        }
        /* Move any pending receive messages to other kcm sockets */
        requeue_rx_msgs(mux, &sk->sk_receive_queue);