netdev - Re: [PATCH ipsec] xfrm: fix a NULL-ptr deref in xfrm_local

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Message-ID: <20200529104053.GH13121@gauss3.secunet.de>
Date:   Fri, 29 May 2020 12:40:53 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Xin Long <lucien.xin@...il.com>
CC:     <netdev@...r.kernel.org>, Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Sabrina Dubroca <sd@...asysnail.net>
Subject: Re: [PATCH ipsec] xfrm: fix a NULL-ptr deref in xfrm_local_error

On Tue, May 26, 2020 at 05:41:46PM +0800, Xin Long wrote:
> This patch is to fix a crash:
> 
>   [ ] kasan: GPF could be caused by NULL-ptr deref or user memory access
>   [ ] general protection fault: 0000 [#1] SMP KASAN PTI
>   [ ] RIP: 0010:ipv6_local_error+0xac/0x7a0
>   [ ] Call Trace:
>   [ ]  xfrm6_local_error+0x1eb/0x300
>   [ ]  xfrm_local_error+0x95/0x130
>   [ ]  __xfrm6_output+0x65f/0xb50
>   [ ]  xfrm6_output+0x106/0x46f
>   [ ]  udp_tunnel6_xmit_skb+0x618/0xbf0 [ip6_udp_tunnel]
>   [ ]  vxlan_xmit_one+0xbc6/0x2c60 [vxlan]
>   [ ]  vxlan_xmit+0x6a0/0x4276 [vxlan]
>   [ ]  dev_hard_start_xmit+0x165/0x820
>   [ ]  __dev_queue_xmit+0x1ff0/0x2b90
>   [ ]  ip_finish_output2+0xd3e/0x1480
>   [ ]  ip_do_fragment+0x182d/0x2210
>   [ ]  ip_output+0x1d0/0x510
>   [ ]  ip_send_skb+0x37/0xa0
>   [ ]  raw_sendmsg+0x1b4c/0x2b80
>   [ ]  sock_sendmsg+0xc0/0x110
> 
> This occurred when sending a v4 skb over vxlan6 over ipsec, in which case
> skb->protocol == htons(ETH_P_IPV6) while skb->sk->sk_family == AF_INET in
> xfrm_local_error(). Then it will go to xfrm6_local_error() where it tries
> to get ipv6 info from a ipv4 sk.
> 
> This issue was actually fixed by Commit 628e341f319f ("xfrm: make local
> error reporting more robust"), but brought back by Commit 844d48746e4b
> ("xfrm: choose protocol family by skb protocol").
> 
> So to fix it, we should call xfrm6_local_error() only when skb->protocol
> is htons(ETH_P_IPV6) and skb->sk->sk_family is AF_INET6.
> 
> Fixes: 844d48746e4b ("xfrm: choose protocol family by skb protocol")
> Reported-by: Xiumei Mu <xmu@...hat.com>
> Signed-off-by: Xin Long <lucien.xin@...il.com>

Patch applied, thanks Xin!