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Date:   Fri, 23 Sep 2022 11:23:13 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "liujian (CE)" <liujian56@...wei.com>
Cc:     "me@...i.io" <me@...i.io>, davem <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net v2] tun: Check tun device queue status in tun_chr_write_iter

On Thu, Sep 22, 2022 at 9:45 PM liujian (CE) <liujian56@...wei.com> wrote:
>
>
>
> > -----Original Message-----
> > From: liujian (CE)
> > Sent: Friday, September 16, 2022 3:05 PM
> > To: 'Jason Wang' <jasowang@...hat.com>
> > Cc: davem <davem@...emloft.net>; Eric Dumazet
> > <edumazet@...gle.com>; Jakub Kicinski <kuba@...nel.org>; Paolo Abeni
> > <pabeni@...hat.com>; Alexei Starovoitov <ast@...nel.org>; Daniel
> > Borkmann <daniel@...earbox.net>; Jesper Dangaard Brouer
> > <hawk@...nel.org>; John Fastabend <john.fastabend@...il.com>; netdev
> > <netdev@...r.kernel.org>
> > Subject: RE: [PATCH net v2] tun: Check tun device queue status in
> > tun_chr_write_iter
> >
> >
> >
> > > -----Original Message-----
> > > From: Jason Wang [mailto:jasowang@...hat.com]
> > > Sent: Friday, September 16, 2022 9:57 AM
> > > To: liujian (CE) <liujian56@...wei.com>
> > > Cc: davem <davem@...emloft.net>; Eric Dumazet
> > <edumazet@...gle.com>;
> > > Jakub Kicinski <kuba@...nel.org>; Paolo Abeni <pabeni@...hat.com>;
> > > Alexei Starovoitov <ast@...nel.org>; Daniel Borkmann
> > > <daniel@...earbox.net>; Jesper Dangaard Brouer <hawk@...nel.org>;
> > John
> > > Fastabend <john.fastabend@...il.com>; netdev
> > <netdev@...r.kernel.org>
> > > Subject: Re: [PATCH net v2] tun: Check tun device queue status in
> > > tun_chr_write_iter
> > >
> > > On Thu, Sep 15, 2022 at 8:34 PM Liu Jian <liujian56@...wei.com> wrote:
> > > >
> > > > syzbot found below warning:
> > > >
> > > > ------------[ cut here ]------------
> > > > geneve0 received packet on queue 3, but number of RX queues is 3
> > > > WARNING: CPU: 1 PID: 29734 at net/core/dev.c:4611 netif_get_rxqueue
> > > > net/core/dev.c:4611 [inline]
> > > > WARNING: CPU: 1 PID: 29734 at net/core/dev.c:4611
> > > > netif_receive_generic_xdp+0xb10/0xb50 net/core/dev.c:4683 Modules
> > > linked in:
> > > > CPU: 1 PID: 29734 Comm: syz-executor.0 Not tainted 5.10.0 #5
> > > > Hardware
> > > > name: linux,dummy-virt (DT)
> > > > pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--) pc :
> > > > netif_get_rxqueue net/core/dev.c:4611 [inline] pc :
> > > > netif_receive_generic_xdp+0xb10/0xb50 net/core/dev.c:4683 lr :
> > > > netif_get_rxqueue net/core/dev.c:4611 [inline] lr :
> > > > netif_receive_generic_xdp+0xb10/0xb50 net/core/dev.c:4683 sp :
> > > > ffffa00016127770
> > > > x29: ffffa00016127770 x28: ffff3f4607d6acb4
> > > > x27: ffff3f4607d6acb0 x26: ffff3f4607d6ad20
> > > > x25: ffff3f461de3c000 x24: ffff3f4607d6ad28
> > > > x23: ffffa00010059000 x22: ffff3f4608719100
> > > > x21: 0000000000000003 x20: ffffa000161278a0
> > > > x19: ffff3f4607d6ac40 x18: 0000000000000000
> > > > x17: 0000000000000000 x16: 00000000f2f2f204
> > > > x15: 00000000f2f20000 x14: 6465766965636572
> > > > x13: 20306576656e6567 x12: ffff98b8ed3b924d
> > > > x11: 1ffff8b8ed3b924c x10: ffff98b8ed3b924c
> > > > x9 : ffffc5c76525c9c4 x8 : 0000000000000000
> > > > x7 : 0000000000000001 x6 : ffff98b8ed3b924c
> > > > x5 : ffff3f460f3b29c0 x4 : dfffa00000000000
> > > > x3 : ffffc5c765000000 x2 : 0000000000000000
> > > > x1 : 0000000000000000 x0 : ffff3f460f3b29c0 Call trace:
> > > >  netif_get_rxqueue net/core/dev.c:4611 [inline]
> > > >  netif_receive_generic_xdp+0xb10/0xb50 net/core/dev.c:4683
> > > > do_xdp_generic net/core/dev.c:4777 [inline]
> > > >  do_xdp_generic+0x9c/0x190 net/core/dev.c:4770
> > > >  tun_get_user+0xd94/0x2010 drivers/net/tun.c:1938
> > > >  tun_chr_write_iter+0x98/0x100 drivers/net/tun.c:2036
> > > > call_write_iter
> > > > include/linux/fs.h:1960 [inline]
> > > >  new_sync_write+0x260/0x370 fs/read_write.c:515
> > > > vfs_write+0x51c/0x61c
> > > > fs/read_write.c:602
> > > >  ksys_write+0xfc/0x200 fs/read_write.c:655  __do_sys_write
> > > > fs/read_write.c:667 [inline]  __se_sys_write fs/read_write.c:664
> > > > [inline]
> > > >  __arm64_sys_write+0x50/0x60 fs/read_write.c:664  __invoke_syscall
> > > > arch/arm64/kernel/syscall.c:36 [inline]  invoke_syscall
> > > > arch/arm64/kernel/syscall.c:48 [inline]
> > > >  el0_svc_common.constprop.0+0xf4/0x414
> > > > arch/arm64/kernel/syscall.c:155 do_el0_svc+0x50/0x11c
> > > > arch/arm64/kernel/syscall.c:217
> > > >  el0_svc+0x20/0x30 arch/arm64/kernel/entry-common.c:353
> > > >  el0_sync_handler+0xe4/0x1e0 arch/arm64/kernel/entry-common.c:369
> > > >  el0_sync+0x148/0x180 arch/arm64/kernel/entry.S:683
> > > >
> > > > This is because the detached queue is used to send data. Therefore,
> > > > we need to check the queue status in the tun_chr_write_iter function.
> > > >
> > > > Fixes: cde8b15f1aab ("tuntap: add ioctl to attach or detach a file
> > > > form tuntap device")
> > >
> Hello,
> Sorry, fixes tag is wrong. The warning should be introduced by commit 3fe260e00cd0 (" net: tun: record RX queue in skb before do_xdp_generic() "). Before this, do_xdp_generic always uses queue0. Therefore, when the warning is generated due to detached, queue0 is used and is printed only once, which is harmless. So it's not a problem.
> What do you think about  this warning?

I tend to keep this warning (it might be too late to fix).

Thanks

>
> > > Not sure this deserves a stable.
> > >
> > > > Signed-off-by: Liu Jian <liujian56@...wei.com>
> > > > ---
> > > > v1->v2: add fixes tag
> > > >  drivers/net/tun.c | 5 +++++
> > > >  1 file changed, 5 insertions(+)
> > > >
> > > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c index
> > > > 259b2b84b2b3..261411c1a6bb 100644
> > > > --- a/drivers/net/tun.c
> > > > +++ b/drivers/net/tun.c
> > > > @@ -2019,6 +2019,11 @@ static ssize_t tun_chr_write_iter(struct
> > > > kiocb
> > > *iocb, struct iov_iter *from)
> > > >         if (!tun)
> > > >                 return -EBADFD;
> > > >
> > > > +       if (tfile->detached) {
> > >
> > > tfile->detached is synchronized through rtnl_lock which is probably
> > > not suitable for the datapath. We probably need to rcuify this.
> > >
> > > > +               tun_put(tun);
> > > > +               return -ENETDOWN;
> > >
> > > Another question is that can some user space depend on this behaviour?
> > > I wonder if it's more safe to pretend the packet was received here?
> > >
> > Thanks for your review. I don't know whether there was any depend on this
> > behavior.
> > If that's the case, I think it's better to keep this warning.
> > What is your opinion on this warning?
> >
> > > Thanks
> > >
> > > > +       }
> > > > +
> > > >         if ((file->f_flags & O_NONBLOCK) || (iocb->ki_flags & IOCB_NOWAIT))
> > > >                 noblock = 1;
> > > >
> > > > --
> > > > 2.17.1
> > > >
>

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