skbuff: fix a data race in skb_queue_len() (86b18aaa) · Commits · 戴 / test

sk_buff.qlen can be accessed concurrently as noticed by KCSAN, BUG: KCSAN: data-race in __skb_try_recv_from_queue / unix_dgram_sendmsg read to 0xffff8a1b1d8a81c0 of 4 bytes by task 5371 on cpu 96: unix_dgram_sendmsg+0x9a9/0xb70 include/linux/skbuff.h:1821 net/unix/af_unix.c:1761 ____sys_sendmsg+0x33e/0x370 ___sys_sendmsg+0xa6/0xf0 __sys_sendmsg+0x69/0xf0 __x64_sys_sendmsg+0x51/0x70 do_syscall_64+0x91/0xb47 entry_SYSCALL_64_after_hwframe+0x49/0xbe write to 0xffff8a1b1d8a81c0 of 4 bytes by task 1 on cpu 99: __skb_try_recv_from_queue+0x327/0x410 include/linux/skbuff.h:2029 __skb_try_recv_datagram+0xbe/0x220 unix_dgram_recvmsg+0xee/0x850 ____sys_recvmsg+0x1fb/0x210 ___sys_recvmsg+0xa2/0xf0 __sys_recvmsg+0x66/0xf0 __x64_sys_recvmsg+0x51/0x70 do_syscall_64+0x91/0xb47 entry_SYSCALL_64_after_hwframe+0x49/0xbe Since only the read is operating as lockless, it could introduce a logic bug in unix_recvq_full() due to the load tearing. Fix it by adding a lockless variant of skb_queue_len() and unix_recvq_full() where READ_ONCE() is on the read while WRITE_ONCE() is on the write similar to the commit ("net: add skb_queue_empty_lockless()"). Signed-off-by:

Qian Cai <cai@lca.pw> Signed-off-by:

David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

+13 −1

Original line number	Diff line number	Diff line
		@@ -1821,6 +1821,18 @@ static inline __u32 skb_queue_len(const struct sk_buff_head *list_)
		return list_->qlen;
		}

		/**
		* skb_queue_len_lockless - get queue length
		* @list_: list to measure
		*
		* Return the length of an &sk_buff queue.
		* This variant can be used in lockless contexts.
		*/
		static inline __u32 skb_queue_len_lockless(const struct sk_buff_head *list_)
		{
		return READ_ONCE(list_->qlen);
		}

		/**
		* __skb_queue_head_init - initialize non-spinlock portions of sk_buff_head
		* @list: queue to initialize
		@@ -2026,7 +2038,7 @@ static inline void __skb_unlink(struct sk_buff skb, struct sk_buff_head list)
		{
		struct sk_buff next, prev;

		list->qlen--;
		WRITE_ONCE(list->qlen, list->qlen - 1);
		next = skb->next;
		prev = skb->prev;
		skb->next = skb->prev = NULL;

net/unix/af_unix.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -189,11 +189,17 @@ static inline int unix_may_send(struct sock sk, struct sock osk)
		return unix_peer(osk) == NULL \|\| unix_our_peer(sk, osk);
		}

		static inline int unix_recvq_full(struct sock const *sk)
		static inline int unix_recvq_full(const struct sock *sk)
		{
		return skb_queue_len(&sk->sk_receive_queue) > sk->sk_max_ack_backlog;
		}

		static inline int unix_recvq_full_lockless(const struct sock *sk)
		{
		return skb_queue_len_lockless(&sk->sk_receive_queue) >
		READ_ONCE(sk->sk_max_ack_backlog);
		}

		struct sock unix_peer_get(struct sock s)
		{
		struct sock *peer;
		@@ -1758,7 +1764,8 @@ restart_locked:
		* - unix_peer(sk) == sk by time of get but disconnected before lock
		*/
		if (other != sk &&
		unlikely(unix_peer(other) != sk && unix_recvq_full(other))) {
		unlikely(unix_peer(other) != sk &&
		unix_recvq_full_lockless(other))) {
		if (timeo) {
		timeo = unix_wait_for_peer(other, timeo);

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