Subject: Re: [PATCH net-next] seg6: fix parameter passing when calling NF_HOOK() in End.DX4 and End.DX6 behaviors

From: Simon Horman <[email-masked]>
Date: Mon, 3 Jun 2024 19:21:16 +0100

On Thu, May 30, 2024 at 03:43:38PM +0800, Jianguo Wu wrote:
> From: Jianguo Wu <[email-masked]>
> 
> input_action_end_dx4() and input_action_end_dx6() call NF_HOOK() for PREROUTING hook,
> for PREROUTING hook, we should passing a valid indev, and a NULL outdev to NF_HOOK(),
> otherwise may trigger a NULL pointer dereference, as below:

nit: The text above should be line-wrapped so that it is
     no more than 75 columns wide.

Link: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes

> 
>     [74830.647293] BUG: kernel NULL pointer dereference, address: 0000000000000090
>     [74830.655633] #PF: supervisor read access in kernel mode
>     [74830.657888] #PF: error_code(0x0000) - not-present page
>     [74830.659500] PGD 0 P4D 0
>     [74830.660450] Oops: 0000 [#1] PREEMPT SMP PTI
>     ...
>     [74830.664953] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
>     [74830.666569] RIP: 0010:rpfilter_mt+0x44/0x15e [ipt_rpfilter]
>     ...
>     [74830.689725] Call Trace:
>     [74830.690402]  <IRQ>
>     [74830.690953]  ? show_trace_log_lvl+0x1c4/0x2df
>     [74830.692020]  ? show_trace_log_lvl+0x1c4/0x2df
>     [74830.693095]  ? ipt_do_table+0x286/0x710 [ip_tables]
>     [74830.694275]  ? __die_body.cold+0x8/0xd
>     [74830.695205]  ? page_fault_oops+0xac/0x140
>     [74830.696244]  ? exc_page_fault+0x62/0x150
>     [74830.697225]  ? asm_exc_page_fault+0x22/0x30
>     [74830.698344]  ? rpfilter_mt+0x44/0x15e [ipt_rpfilter]
>     [74830.699540]  ipt_do_table+0x286/0x710 [ip_tables]
>     [74830.700758]  ? ip6_route_input+0x19d/0x240
>     [74830.701752]  nf_hook_slow+0x3f/0xb0
>     [74830.702678]  input_action_end_dx4+0x19b/0x1e0
>     [74830.703735]  ? input_action_end_t+0xe0/0xe0
>     [74830.704734]  seg6_local_input_core+0x2d/0x60
>     [74830.705782]  lwtunnel_input+0x5b/0xb0
>     [74830.706690]  __netif_receive_skb_one_core+0x63/0xa0
>     [74830.707825]  process_backlog+0x99/0x140
>     [74830.709538]  __napi_poll+0x2c/0x160
>     [74830.710673]  net_rx_action+0x296/0x350
>     [74830.711860]  __do_softirq+0xcb/0x2ac
>     [74830.713049]  do_softirq+0x63/0x90
> 
> input_action_end_dx4() passing a NULL indev to NF_HOOK(), and finally trigger a
> NULL dereference in rpfilter_mt()->rpfilter_is_loopback():
>     static bool
>     rpfilter_is_loopback(const struct sk_buff *skb, const struct net_device *in)
>     {
>             // in is NULL
>             return skb->pkt_type == PACKET_LOOPBACK || in->flags & IFF_LOOPBACK;
>     }
> 
> Fixes: 7a3f5b0de364 ("netfilter: add netfilter hooks to SRv6 data plane")

nit: no blank line here.

> 
> Signed-off-by: Jianguo Wu <[email-masked]>

I am slightly puzzled that this bug was in
the tree for so long without being noticed.

But the above not withstanding, this looks good to me.

Reviewed-by: Simon Horman <[email-masked]>

...