[PATCH AUTOSEL 4.4 23/64] skbuff: fix a data race in skb_queue_len()
From: Sasha Levin <sashal@kernel.org>
Date: 2020-09-18 02:17:39
Also in:
lkml, stable
Subsystem:
networking [general], networking [unix sockets], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Kuniyuki Iwashima, Linus Torvalds
From: Qian Cai <redacted>
[ Upstream commit 86b18aaa2b5b5bb48e609cd591b3d2d0fdbe0442 ]
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 d7d16a89350a ("net: add skb_queue_empty_lockless()").
Signed-off-by: Qian Cai <redacted>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/skbuff.h | 14 +++++++++++++-
net/unix/af_unix.c | 11 +++++++++--
2 files changed, 22 insertions(+), 3 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 735ff1525f485..ffd698f70a84e 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h@@ -1438,6 +1438,18 @@ 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
@@ -1641,7 +1653,7 @@ 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;
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index b5e2ef242efe7..ac78c5ac82846 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c@@ -191,11 +191,17 @@ 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;
@@ -1792,7 +1798,8 @@ 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);
--
2.25.1