kongweibin reported a kernel panic in ip6_forward() when input interface
has no in6 dev associated.

The following tc commands were used to reproduce this panic:
tc qdisc del dev vxlan100 root
tc qdisc add dev vxlan100 root netem corrupt 5%

CC: stable@vger.kernel.org
Fixes: ccd27f05ae7b ("ipv6: fix 'disable_policy' for fwd packets")
Reported-by: kongweibin <kongweibin2@huawei.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
---

kongweibin, could you test this patch with your setup?

Thanks,
Nicolas

 net/ipv6/ip6_output.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index e23f058166af..fa63ef2bd99c 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -485,7 +485,7 @@ int ip6_forward(struct sk_buff *skb)
 		goto drop;
 
 	if (!net->ipv6.devconf_all->disable_policy &&
-	    !idev->cnf.disable_policy &&
+	    (!idev || !idev->cnf.disable_policy) &&
 	    !xfrm6_policy_check(NULL, XFRM_POLICY_FWD, skb)) {
 		__IP6_INC_STATS(net, idev, IPSTATS_MIB_INDISCARDS);
 		goto drop;
-- 
2.33.0

Hello:

This patch was applied to netdev/net.git (master)
by David S. Miller <davem@davemloft.net>:

On Fri,  8 Apr 2022 16:03:42 +0200 you wrote:
> kongweibin reported a kernel panic in ip6_forward() when input interface
> has no in6 dev associated.
> 
> The following tc commands were used to reproduce this panic:
> tc qdisc del dev vxlan100 root
> tc qdisc add dev vxlan100 root netem corrupt 5%
> 
> [...]

Here is the summary with links:
  - [net] ipv6: fix panic when forwarding a pkt with no in6 dev
    https://git.kernel.org/netdev/net/c/e3fa461d8b0e

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

On 4/8/22 8:03 AM, Nicolas Dichtel wrote:
> kongweibin reported a kernel panic in ip6_forward() when input interface
> has no in6 dev associated.
> 
> The following tc commands were used to reproduce this panic:
> tc qdisc del dev vxlan100 root
> tc qdisc add dev vxlan100 root netem corrupt 5%
> 
> CC: stable@vger.kernel.org
> Fixes: ccd27f05ae7b ("ipv6: fix 'disable_policy' for fwd packets")
> Reported-by: kongweibin <kongweibin2@huawei.com>
> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
> ---
> 

Reviewed-by: David Ahern <dsahern@kernel.org>

On 4/8/22 07:03, Nicolas Dichtel wrote:
> kongweibin reported a kernel panic in ip6_forward() when input interface
> has no in6 dev associated.
>
> The following tc commands were used to reproduce this panic:
> tc qdisc del dev vxlan100 root
> tc qdisc add dev vxlan100 root netem corrupt 5%

Not sure I understand how these qdisc changes can trigger a NULL idev ?

Do we have another bug, like skb->cb[] content being mangled ?


>
> CC: stable@vger.kernel.org
> Fixes: ccd27f05ae7b ("ipv6: fix 'disable_policy' for fwd packets")
> Reported-by: kongweibin <kongweibin2@huawei.com>
> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
> ---
>
> kongweibin, could you test this patch with your setup?
>
> Thanks,
> Nicolas
>
>   net/ipv6/ip6_output.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index e23f058166af..fa63ef2bd99c 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -485,7 +485,7 @@ int ip6_forward(struct sk_buff *skb)
>   		goto drop;
>   
>   	if (!net->ipv6.devconf_all->disable_policy &&
> -	    !idev->cnf.disable_policy &&
> +	    (!idev || !idev->cnf.disable_policy) &&
>   	    !xfrm6_policy_check(NULL, XFRM_POLICY_FWD, skb)) {
>   		__IP6_INC_STATS(net, idev, IPSTATS_MIB_INDISCARDS);
>   		goto drop;

> kongweibin, could you test this patch with your setup?
>
> Thanks,
> Nicolas
>
>   net/ipv6/ip6_output.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c index 
> e23f058166af..fa63ef2bd99c 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -485,7 +485,7 @@ int ip6_forward(struct sk_buff *skb)
>   		goto drop;
>   
>   	if (!net->ipv6.devconf_all->disable_policy &&
> -	    !idev->cnf.disable_policy &&
> +	    (!idev || !idev->cnf.disable_policy) &&
>   	    !xfrm6_policy_check(NULL, XFRM_POLICY_FWD, skb)) {
>   		__IP6_INC_STATS(net, idev, IPSTATS_MIB_INDISCARDS);
>   		goto drop;

I have test the patch with my setup, it is OK.



>> kongweibin reported a kernel panic in ip6_forward() when input 
>> interface has no in6 dev associated.
>>
>> The following tc commands were used to reproduce this panic:
>> tc qdisc del dev vxlan100 root
>> tc qdisc add dev vxlan100 root netem corrupt 5%
>
>Not sure I understand how these qdisc changes can trigger a NULL idev ?
>
>Do we have another bug, like skb->cb[] content being mangled ?
>

As for why qdisc makes the idev null, I tracked where the iif assigned in ip6_rcv_core,
there is no problem there.

Not sure what has changed that makes the iif value wrong.