skbuff: fix a data race in skb_queue_len()
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 d7d16a8935
("net: add skb_queue_empty_lockless()").
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
parent
c35947b8ff
commit
86b18aaa2b
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@ -1821,6 +1821,18 @@ static inline __u32 skb_queue_len(const struct sk_buff_head *list_)
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return list_->qlen;
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}
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/**
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* skb_queue_len_lockless - get queue length
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* @list_: list to measure
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*
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* Return the length of an &sk_buff queue.
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* This variant can be used in lockless contexts.
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*/
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static inline __u32 skb_queue_len_lockless(const struct sk_buff_head *list_)
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{
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return READ_ONCE(list_->qlen);
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}
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/**
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* __skb_queue_head_init - initialize non-spinlock portions of sk_buff_head
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* @list: queue to initialize
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@ -2026,7 +2038,7 @@ static inline void __skb_unlink(struct sk_buff *skb, struct sk_buff_head *list)
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{
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struct sk_buff *next, *prev;
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list->qlen--;
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WRITE_ONCE(list->qlen, list->qlen - 1);
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next = skb->next;
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prev = skb->prev;
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skb->next = skb->prev = NULL;
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@ -189,11 +189,17 @@ static inline int unix_may_send(struct sock *sk, struct sock *osk)
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return unix_peer(osk) == NULL || unix_our_peer(sk, osk);
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}
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static inline int unix_recvq_full(struct sock const *sk)
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static inline int unix_recvq_full(const struct sock *sk)
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{
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return skb_queue_len(&sk->sk_receive_queue) > sk->sk_max_ack_backlog;
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}
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static inline int unix_recvq_full_lockless(const struct sock *sk)
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{
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return skb_queue_len_lockless(&sk->sk_receive_queue) >
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READ_ONCE(sk->sk_max_ack_backlog);
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}
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struct sock *unix_peer_get(struct sock *s)
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{
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struct sock *peer;
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@ -1758,7 +1764,8 @@ restart_locked:
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* - unix_peer(sk) == sk by time of get but disconnected before lock
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*/
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if (other != sk &&
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unlikely(unix_peer(other) != sk && unix_recvq_full(other))) {
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unlikely(unix_peer(other) != sk &&
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unix_recvq_full_lockless(other))) {
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if (timeo) {
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timeo = unix_wait_for_peer(other, timeo);
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