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

[Pavan Chebbi]

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)
>                 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
>

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