Re: [PATCH] net: check for dev pointer being NULL in dev_hard_header() to avoid GPF

[Eric Dumazet]

On Thu, Dec 1, 2022 at 2:16 PM Pavan Chebbi <pavan.chebbi@xxxxxxxxxxxx> wrote:
>
> On Wed, Nov 30, 2022 at 7:43 PM George Kennedy
> <george.kennedy@xxxxxxxxxx> wrote:
> >
> > The dev pointer can be NULL in dev_hard_header(). Add check for dev being
> > NULL in dev_hard_header() to avoid GPF.
> >
> > general protection fault, probably for non-canonical address
> >     0xdffffc0000000046: 0000 [#1] PREEMPT SMP KASAN NOPTI
> > KASAN: null-ptr-deref in range [0x0000000000000230-0x0000000000000237]
> > CPU: 1 PID: 45 Comm: kworker/1:1 Not tainted 6.1.0-rc7+ #2
> > Hardware name: Red Hat KVM, BIOS 1.15.0-2.module+el8.6.0+20659+3dcf7c70
> > Workqueue: mld mld_ifc_work
> > RIP: 0010:macvlan_hard_header (./include/linux/netdevice.h:3057
> >     (discriminator 4) drivers/net/macvlan.c:594 (discriminator 4))
> > RSP: 0018:ffff888103d377d0 EFLAGS: 00010212
> > RAX: dffffc0000000000 RBX: ffff88801cf1a000 RCX: 0000000000000000
> > RDX: 0000000000000046 RSI: 0000000000000000 RDI: 0000000000000230
> > RBP: ffff88801e8ef328 R08: 0000000000000000 R09: 0000000000000060
> > R10: 0000000000000000 R11: 0000000000000000 R12: ffff88801f0497c0
> > R13: 0000000000000000 R14: ffff888045187c98 R15: 0000000000000060
> > FS:  0000000000000000(0000) GS:ffff888106c80000(0000)
> >     knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00007fbf3f1c1840 CR3: 0000000014e36000 CR4: 00000000000006e0
> > Call Trace:
> >  <TASK>
> > neigh_connected_output (./include/linux/netdevice.h:3060
> >     net/core/neighbour.c:1595)
> > ip6_finish_output2 (./include/net/neighbour.h:546
> >     net/ipv6/ip6_output.c:134)
> > ip6_finish_output (net/ipv6/ip6_output.c:195 net/ipv6/ip6_output.c:206)
> > ip6_output (./include/linux/netfilter.h:291 net/ipv6/ip6_output.c:227)
> > NF_HOOK.constprop.0 (./include/net/dst.h:445
> >     ./include/linux/netfilter.h:302)
> > mld_sendpack (net/ipv6/mcast.c:1824)
> > mld_send_cr (net/ipv6/mcast.c:2122)
> > mld_ifc_work (net/ipv6/mcast.c:2655)
> > process_one_work (kernel/workqueue.c:2294)
> > worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2437)
> > kthread (kernel/kthread.c:376)
> > ret_from_fork (arch/x86/entry/entry_64.S:312)
> >  </TASK>
> > Modules linked in:
> > Dumping ftrace buffer:
> >    (ftrace buffer empty)
> > ---[ end trace 0000000000000000 ]---
> >
> > Fixes: 0c4e85813d0a ("[NET]: Wrap netdevice hardware header creation.")
> > Reported-by: syzkaller <syzkaller@xxxxxxxxxxxxxxxx>
> > Signed-off-by: George Kennedy <george.kennedy@xxxxxxxxxx>
> > ---
> >  include/linux/netdevice.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > index eddf8ee270e7..9b25a6301fa5 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -3054,7 +3054,7 @@ static inline int dev_hard_header(struct sk_buff *skb, struct net_device *dev,
> >                                   const void *daddr, const void *saddr,
> >                                   unsigned int len)
> >  {
> > -       if (!dev->header_ops || !dev->header_ops->create)
> > +       if (!dev || !dev->header_ops || !dev->header_ops->create)

Do  you have a repro ?

This patch will not prevent a crash later I think.

Please fix the root cause, thanks !

> >                 return 0;
>
> net_device being NULL during eth header construction? seems like a
> more serious issue?
> If it indeed is a genuine scenario I think a better description is needed...
>
> >
> >         return dev->header_ops->create(skb, dev, type, daddr, saddr, len);
> > --
> > 2.31.1
> >