@@ -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 @@ static void requeue_rx_msgs(struct kcm_mux *mux, struct sk_buff_head *head)
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);
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> --- net/kcm/kcmsock.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-)