netdev - RE: [PATCH net v2] tun: Check tun device queue status in tun_chr_write

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Date:   Fri, 16 Sep 2022 07:04:49 +0000
From:   "liujian (CE)" <liujian56@...wei.com>
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")
> 
> 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
> >