Messages in this thread | | | Subject | Re: [PATCH] tun: Fix use-after-free in tun_net_xmit | From | YueHaibing <> | Date | Mon, 29 Apr 2019 21:07:07 +0800 |
| |
On 2019/4/29 10:23, Jason Wang wrote: > > On 2019/4/29 上午1:59, Cong Wang wrote: >> On Sun, Apr 28, 2019 at 12:51 AM Jason Wang <jasowang@redhat.com> wrote: >>>> tun_net_xmit() doesn't have the chance to >>>> access the change because it holding the rcu_read_lock(). >>> >>> >>> The problem is the following codes: >>> >>> >>> --tun->numqueues; >>> >>> ... >>> >>> synchronize_net(); >>> >>> We need make sure the decrement of tun->numqueues be visible to readers >>> after synchronize_net(). And in tun_net_xmit(): >> >> It doesn't matter at all. Readers are okay to read it even they still use the >> stale tun->numqueues, as long as the tfile is not freed readers can read >> whatever they want... > > This is only true if we set SOCK_RCU_FREE, isn't it? > >> >> The decrement of tun->numqueues is just how we unpublish the old >> tfile, it is still valid for readers to read it _after_ unpublish, we only need >> to worry about free, not about unpublish. This is the whole spirit of RCU. >> > > The point is we don't convert tun->numqueues to RCU but use > synchronize_net(). > >> You need to rethink about my SOCK_RCU_FREE patch. > > The code is wrote before SOCK_RCU_FREE is introduced and assume no > de-reference from device after synchronize_net(). It doesn't harm to > figure out the root cause which may give us more confidence to the fix > (e.g like SOCK_RCU_FREE). > > I don't object to fix with SOCK_RCU_FREE, but then we should remove > the redundant synchronize_net(). But I still prefer to synchronize > everything explicitly like (completely untested): > >>From df91f77d35a6aa7943b6f2a7d4b329990896a0fe Mon Sep 17 00:00:00 2001 > From: Jason Wang <jasowang@redhat.com> > Date: Mon, 29 Apr 2019 10:21:06 +0800 > Subject: [PATCH] tuntap: synchronize through tfiles instead of numqueues > > Signed-off-by: Jason Wang <jasowang@redhat.com> > --- > drivers/net/tun.c | 11 +++++------ > 1 file changed, 5 insertions(+), 6 deletions(-) > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index 80bff1b4ec17..03715f605fb5 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -698,6 +698,7 @@ static void __tun_detach(struct tun_file *tfile, bool clean) > > rcu_assign_pointer(tun->tfiles[index], > tun->tfiles[tun->numqueues - 1]); > + rcu_assign_pointer(tun->tfiles[tun->numqueues], NULL); > ntfile = rtnl_dereference(tun->tfiles[index]);
move here to avoid NULL pointer dereference, it works for me
rcu_assign_pointer(tun->tfiles[tun->numqueues -1 ], NULL);
> ntfile->queue_index = index; > > @@ -1082,7 +1083,7 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev) > 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)) > @@ -1305,15 +1306,13 @@ static int tun_xdp_xmit(struct net_device *dev, int n, > > rcu_read_lock(); > > - numqueues = READ_ONCE(tun->numqueues); > - if (!numqueues) { > + tfile = rcu_dereference(tun->tfiles[smp_processor_id() % > + tun->numqueues]); > + if (!tfile) { > rcu_read_unlock(); > return -ENXIO; /* Caller will free/return all frames */ > } > > - tfile = rcu_dereference(tun->tfiles[smp_processor_id() % > - numqueues]); > - > spin_lock(&tfile->tx_ring.producer_lock); > for (i = 0; i < n; i++) { > struct xdp_frame *xdp = frames[i]; >
| |