From mboxrd@z Thu Jan  1 00:00:00 1970
From: Nelson Elhage <nelhage@ksplice.com>
Subject: Re: NULL dereference in econet AUN-over-UDP receive
Date: Wed, 8 Dec 2010 23:18:22 -0500
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References: <20101209003015.GA27906@ksplice.com>
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To: David Miller <davem@davemloft.net>
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Yep, that fixes the crash.

Tested-by: Nelson Elhage <nelhage@ksplice.com>

On Wed, Dec 8, 2010 at 9:02 PM, David Miller <davem@davemloft.net> wrot=
e:
> From: Eric Dumazet <eric.dumazet@gmail.com>
> Date: Thu, 09 Dec 2010 02:37:47 +0100
>
>> Le mercredi 08 d=E9cembre 2010 =E0 19:30 -0500, Nelson Elhage a =E9c=
rit :
>>> While testing one of my econet reproducers on a patched kernel, I t=
riggered a
>>> NULL pointer dereference in the econet AUN-over-UDP receive path. U=
pon further
>>> investigation, I now suspect that this code path hasn't worked at a=
ll in years.
>>>
>>> A copy of the oops is below for your reference, but here's my analy=
sis:
>>>
>>> When aun_data_available receives a data packet (ah->code =3D=3D 2),=
 it calls
>>> aun_incoming to process the skb. The start of aun_incoming looks li=
ke:
>>>
>>> static void aun_incoming(struct sk_buff *skb, struct aunhdr *ah, si=
ze_t len)
>>> {
>>> =A0 =A0 =A0struct iphdr *ip =3D ip_hdr(skb);
>>> =A0 =A0 =A0unsigned char stn =3D ntohl(ip->saddr) & 0xff;
>>> =A0 =A0 =A0struct sock *sk =3D NULL;
>>> =A0 =A0 =A0struct sk_buff *newskb;
>>> ---> =A0 =A0 =A0 =A0 struct ec_device *edev =3D skb->dev->ec_ptr;
>>>
>>
>> This can be changed to use skb_dst(skb)->dev instead
>>
>> struct dst *dst =3D skb_dst(skb);
>>
>> if (dst) {
>> =A0 =A0 =A0 dev =3D dst->dev;
>> =A0 =A0 =A0 ...
>> }
>
> Nelson please test if this patch fixes your crash:
>
> econet: Fix crash in aun_incoming().
>
> Unconditional use of skb->dev won't work here,
> try to fetch the econet device via skb_dst()->dev
> instead.
>
> Suggested by Eric Dumazet.
>
> Reported-by: Nelson Elhage <nelhage@ksplice.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>
>
> diff --git a/net/econet/af_econet.c b/net/econet/af_econet.c
> index f180371..15dcc1a 100644
> --- a/net/econet/af_econet.c
> +++ b/net/econet/af_econet.c
> @@ -851,9 +851,13 @@ static void aun_incoming(struct sk_buff *skb, st=
ruct aunhdr *ah, size_t len)
> =A0{
> =A0 =A0 =A0 =A0struct iphdr *ip =3D ip_hdr(skb);
> =A0 =A0 =A0 =A0unsigned char stn =3D ntohl(ip->saddr) & 0xff;
> + =A0 =A0 =A0 struct dst_entry *dst =3D skb_dst(skb);
> + =A0 =A0 =A0 struct ec_device *edev =3D NULL;
> =A0 =A0 =A0 =A0struct sock *sk =3D NULL;
> =A0 =A0 =A0 =A0struct sk_buff *newskb;
> - =A0 =A0 =A0 struct ec_device *edev =3D skb->dev->ec_ptr;
> +
> + =A0 =A0 =A0 if (dst)
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 edev =3D dst->dev->ec_ptr;
>
> =A0 =A0 =A0 =A0if (! edev)
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0goto bad;
>