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References: <20230728100035.32092-1-yuehaibing@huawei.com>
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From:   Eric Dumazet <edumazet@google.com>
Date:   Fri, 28 Jul 2023 12:50:22 +0200
Message-ID: <CANn89iJd5amMy+znSi_fP_zNLB3yta7XKcG7fVFk9h0JWDy6Pg@mail.gmail.com>
Subject: Re: [PATCH] ip6mr: Fix skb_under_panic in ip6mr_cache_report()
To:     Yue Haibing <yuehaibing@huawei.com>
Cc:     davem@davemloft.net, dsahern@kernel.org, kuba@kernel.org,
        pabeni@redhat.com, yoshfuji@linux-ipv6.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Fri, Jul 28, 2023 at 12:01=E2=80=AFPM Yue Haibing <yuehaibing@huawei.com=
> wrote:
>
>  skbuff: skb_under_panic: text:ffffffff88771f69 len:56 put:-4
>  head:ffff88805f86a800 data:ffff887f5f86a850 tail:0x88 end:0x2c0 dev:pim6=
reg
>  ------------[ cut here ]------------
>

> When setup a vlan device on dev pim6reg, DAD ns packet may sent on reg_vi=
f_xmit().
> reg_vif_xmit()
>     ip6mr_cache_report()
>         skb_push(skb, -skb_network_offset(pkt));//skb_network_offset(pkt)=
 is 4
> And skb_push declar as this:
>         void *skb_push(struct sk_buff *skb, unsigned int len);
>                 skb->data -=3D len;
>                 //0xffff888f5f86a84c - 0xfffffffc =3D 0xffff887f5f86a850
> skb->data is set to 0xffff887f5f86a850, which is invalid mem addr, lead t=
o skb_push() fails.
>
> Fixes: 14fb64e1f449 ("[IPV6] MROUTE: Support PIM-SM (SSM).")
> Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
> ---
>  net/ipv6/ip6mr.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
> index cc3d5ad17257..ee9c2ff8b0e4 100644
> --- a/net/ipv6/ip6mr.c
> +++ b/net/ipv6/ip6mr.c
> @@ -1051,9 +1051,9 @@ static int ip6mr_cache_report(const struct mr_table=
 *mrt, struct sk_buff *pkt,
>         int ret;
>
>  #ifdef CONFIG_IPV6_PIMSM_V2
> +       int nhoff =3D skb_network_offset(pkt);
>         if (assert =3D=3D MRT6MSG_WHOLEPKT || assert =3D=3D MRT6MSG_WRMIF=
WHOLE)
> -               skb =3D skb_realloc_headroom(pkt, -skb_network_offset(pkt=
)
> -                                               +sizeof(*msg));
> +               skb =3D skb_realloc_headroom(pkt, -nhoff + sizeof(*msg));
>         else
>  #endif
>                 skb =3D alloc_skb(sizeof(struct ipv6hdr) + sizeof(*msg), =
GFP_ATOMIC);
> @@ -1073,7 +1073,8 @@ static int ip6mr_cache_report(const struct mr_table=
 *mrt, struct sk_buff *pkt,
>                    And all this only to mangle msg->im6_msgtype and
>                    to set msg->im6_mbz to "mbz" :-)
>                  */
> -               skb_push(skb, -skb_network_offset(pkt));
> +               skb->data +=3D nhoff;
> +               skb->len  -=3D nhoff;

__skb_pull(skb, nhoff);

>
>                 skb_push(skb, sizeof(*msg));
>                 skb_reset_transport_header(skb);
> --
> 2.34.1
>