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

[Eric Dumazet]

On Thu, Dec 1, 2022 at 9:44 PM George Kennedy <george.kennedy@xxxxxxxxxx> wrote:
>
>
>
> On 12/1/2022 2:25 PM, Eric Dumazet wrote:
> > 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 ?
> See syzkaller repros attached.
>
> > This patch will not prevent a crash later I think.
>
> The repro ran overnight without failure with the patch applied.

Yes, but the patch is hiding a potential bug that might show up with
other 'repros'



>
> >
> > Please fix the root cause, thanks !
>
> Will try.

Thanks, having a repro definitely should help to find the real bug.

I took a look at macvlan , and could not see how vlan->lowerdev  could
be NULL in the first place.

>
> Thanks,
> George
> >
> >>>                  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
> >>>