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Commit ce5d34a3 authored by Qian Cai's avatar Qian Cai Committed by Greg Kroah-Hartman
Browse files

skbuff: fix a data race in skb_queue_len() 



[ 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: default avatarQian Cai <cai@lca.pw>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 60bc60dd

include/linux/skbuff.h

+13 −1
Original line number Diff line number Diff line
@@ -1549,6 +1549,18 @@ 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
@@ -1752,7 +1764,7 @@ 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
@@ -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;
@@ -1793,7 +1799,8 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg, 
	 * - 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);