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Subject[PATCH 4.19 103/113] tuntap: synchronize through tfiles array instead of tun->numqueues
Date
From: Jason Wang <jasowang@redhat.com>

[ Upstream commit 9871a9e47a2646fe30ae7fd2e67668a8d30912f6 ]

When a queue(tfile) is detached through __tun_detach(), we move the
last enabled tfile to the position where detached one sit but don't
NULL out last position. We expect to synchronize the datapath through
tun->numqueues. Unfortunately, this won't work since we're lacking
sufficient mechanism to order or synchronize the access to
tun->numqueues.

To fix this, NULL out the last position during detaching and check
RCU protected tfile against NULL instead of checking tun->numqueues in
datapath.

Cc: YueHaibing <yuehaibing@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: weiyongjun (A) <weiyongjun1@huawei.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Fixes: c8d68e6be1c3b ("tuntap: multiqueue support")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/tun.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -708,6 +708,8 @@ static void __tun_detach(struct tun_file
tun->tfiles[tun->numqueues - 1]);
ntfile = rtnl_dereference(tun->tfiles[index]);
ntfile->queue_index = index;
+ rcu_assign_pointer(tun->tfiles[tun->numqueues - 1],
+ NULL);

--tun->numqueues;
if (clean) {
@@ -1090,7 +1092,7 @@ static netdev_tx_t tun_net_xmit(struct s
tfile = rcu_dereference(tun->tfiles[txq]);

/* Drop packet if interface is not attached */
- if (txq >= tun->numqueues)
+ if (!tfile)
goto drop;

if (!rcu_dereference(tun->steering_prog))
@@ -1281,6 +1283,7 @@ static int tun_xdp_xmit(struct net_devic

rcu_read_lock();

+resample:
numqueues = READ_ONCE(tun->numqueues);
if (!numqueues) {
rcu_read_unlock();
@@ -1289,6 +1292,8 @@ static int tun_xdp_xmit(struct net_devic

tfile = rcu_dereference(tun->tfiles[smp_processor_id() %
numqueues]);
+ if (unlikely(!tfile))
+ goto resample;

spin_lock(&tfile->tx_ring.producer_lock);
for (i = 0; i < n; i++) {

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