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Subject[PATCH 4.14 43/62] udp: use skb_queue_empty_lockless()
Date
From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 137a0dbe3426fd7bcfe3f8117b36a87b3590e4eb ]

syzbot reported a data-race [1].

We should use skb_queue_empty_lockless() to document that we are
not ensuring a mutual exclusion and silence KCSAN.

[1]
BUG: KCSAN: data-race in __skb_recv_udp / __udp_enqueue_schedule_skb

write to 0xffff888122474b50 of 8 bytes by interrupt on cpu 0:
__skb_insert include/linux/skbuff.h:1852 [inline]
__skb_queue_before include/linux/skbuff.h:1958 [inline]
__skb_queue_tail include/linux/skbuff.h:1991 [inline]
__udp_enqueue_schedule_skb+0x2c1/0x410 net/ipv4/udp.c:1470
__udp_queue_rcv_skb net/ipv4/udp.c:1940 [inline]
udp_queue_rcv_one_skb+0x7bd/0xc70 net/ipv4/udp.c:2057
udp_queue_rcv_skb+0xb5/0x400 net/ipv4/udp.c:2074
udp_unicast_rcv_skb.isra.0+0x7e/0x1c0 net/ipv4/udp.c:2233
__udp4_lib_rcv+0xa44/0x17c0 net/ipv4/udp.c:2300
udp_rcv+0x2b/0x40 net/ipv4/udp.c:2470
ip_protocol_deliver_rcu+0x4d/0x420 net/ipv4/ip_input.c:204
ip_local_deliver_finish+0x110/0x140 net/ipv4/ip_input.c:231
NF_HOOK include/linux/netfilter.h:305 [inline]
NF_HOOK include/linux/netfilter.h:299 [inline]
ip_local_deliver+0x133/0x210 net/ipv4/ip_input.c:252
dst_input include/net/dst.h:442 [inline]
ip_rcv_finish+0x121/0x160 net/ipv4/ip_input.c:413
NF_HOOK include/linux/netfilter.h:305 [inline]
NF_HOOK include/linux/netfilter.h:299 [inline]
ip_rcv+0x18f/0x1a0 net/ipv4/ip_input.c:523
__netif_receive_skb_one_core+0xa7/0xe0 net/core/dev.c:5010
__netif_receive_skb+0x37/0xf0 net/core/dev.c:5124
process_backlog+0x1d3/0x420 net/core/dev.c:5955

read to 0xffff888122474b50 of 8 bytes by task 8921 on cpu 1:
skb_queue_empty include/linux/skbuff.h:1494 [inline]
__skb_recv_udp+0x18d/0x500 net/ipv4/udp.c:1653
udp_recvmsg+0xe1/0xb10 net/ipv4/udp.c:1712
inet_recvmsg+0xbb/0x250 net/ipv4/af_inet.c:838
sock_recvmsg_nosec+0x5c/0x70 net/socket.c:871
___sys_recvmsg+0x1a0/0x3e0 net/socket.c:2480
do_recvmmsg+0x19a/0x5c0 net/socket.c:2601
__sys_recvmmsg+0x1ef/0x200 net/socket.c:2680
__do_sys_recvmmsg net/socket.c:2703 [inline]
__se_sys_recvmmsg net/socket.c:2696 [inline]
__x64_sys_recvmmsg+0x89/0xb0 net/socket.c:2696
do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8921 Comm: syz-executor.4 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/udp.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1468,7 +1468,7 @@ static int first_packet_length(struct so

spin_lock_bh(&rcvq->lock);
skb = __first_packet_length(sk, rcvq, &total);
- if (!skb && !skb_queue_empty(sk_queue)) {
+ if (!skb && !skb_queue_empty_lockless(sk_queue)) {
spin_lock(&sk_queue->lock);
skb_queue_splice_tail_init(sk_queue, rcvq);
spin_unlock(&sk_queue->lock);
@@ -1543,7 +1543,7 @@ struct sk_buff *__skb_recv_udp(struct so
return skb;
}

- if (skb_queue_empty(sk_queue)) {
+ if (skb_queue_empty_lockless(sk_queue)) {
spin_unlock_bh(&queue->lock);
goto busy_check;
}
@@ -1570,7 +1570,7 @@ busy_check:
break;

sk_busy_loop(sk, flags & MSG_DONTWAIT);
- } while (!skb_queue_empty(sk_queue));
+ } while (!skb_queue_empty_lockless(sk_queue));

/* sk_queue is empty, reader_queue may contain peeked packets */
} while (timeo &&

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