[Patch net] gre: refetch erspan header from skb->data after pskb_may_pull()

[Patch net] gre: refetch erspan header from skb->data after pskb_may_pull()

[Cong Wang]

After pskb_may_pull() we should always refetch the header
pointers from the skb->data in case it got reallocated.

In gre_parse_header(), the erspan header is still fetched
from the 'options' pointer which is fetched before
pskb_may_pull().

Found this during code review of a KMSAN bug report.

Fixes: cb73ee40b1b3 ("net: ip_gre: use erspan key field for tunnel lookup")
Cc: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
 net/ipv4/gre_demux.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/gre_demux.c b/net/ipv4/gre_demux.c
index 44bfeecac33e..5fd6e8ed02b5 100644
--- a/net/ipv4/gre_demux.c
+++ b/net/ipv4/gre_demux.c
@@ -127,7 +127,7 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 		if (!pskb_may_pull(skb, nhs + hdr_len + sizeof(*ershdr)))
 			return -EINVAL;
 
-		ershdr = (struct erspan_base_hdr *)options;
+		ershdr = (struct erspan_base_hdr *)(skb->data + nhs + hdr_len);
 		tpi->key = cpu_to_be32(get_session_id(ershdr));
 	}
 
-- 
2.21.0

Re: [Patch net] gre: refetch erspan header from skb->data after pskb_may_pull()

[Simon Horman]

Hi Cong,

On Thu, Dec 05, 2019 at 07:39:02PM -0800, Cong Wang wrote:
> After pskb_may_pull() we should always refetch the header
> pointers from the skb->data in case it got reallocated.
> 
> In gre_parse_header(), the erspan header is still fetched
> from the 'options' pointer which is fetched before
> pskb_may_pull().
> 
> Found this during code review of a KMSAN bug report.
> 
> Fixes: cb73ee40b1b3 ("net: ip_gre: use erspan key field for tunnel lookup")
> Cc: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
> ---
>  net/ipv4/gre_demux.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/gre_demux.c b/net/ipv4/gre_demux.c
> index 44bfeecac33e..5fd6e8ed02b5 100644
> --- a/net/ipv4/gre_demux.c
> +++ b/net/ipv4/gre_demux.c
> @@ -127,7 +127,7 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
>  		if (!pskb_may_pull(skb, nhs + hdr_len + sizeof(*ershdr)))
>  			return -EINVAL;
>  
> -		ershdr = (struct erspan_base_hdr *)options;
> +		ershdr = (struct erspan_base_hdr *)(skb->data + nhs + hdr_len);

It seems to me that in the case of WCCPv2 hdr_len will be 4 bytes longer
than where options would be advanced to. Is that a problem here?

>  		tpi->key = cpu_to_be32(get_session_id(ershdr));
>  	}
>  
> -- 
> 2.21.0
> 

Re: [Patch net] gre: refetch erspan header from skb->data after pskb_may_pull()

[Lorenzo Bianconi]

>
> Hi Cong,
>
> On Thu, Dec 05, 2019 at 07:39:02PM -0800, Cong Wang wrote:
> > After pskb_may_pull() we should always refetch the header
> > pointers from the skb->data in case it got reallocated.
> >
> > In gre_parse_header(), the erspan header is still fetched
> > from the 'options' pointer which is fetched before
> > pskb_may_pull().
> >
> > Found this during code review of a KMSAN bug report.
> >
> > Fixes: cb73ee40b1b3 ("net: ip_gre: use erspan key field for tunnel lookup")
> > Cc: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
> > Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
> > ---
> >  net/ipv4/gre_demux.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/ipv4/gre_demux.c b/net/ipv4/gre_demux.c
> > index 44bfeecac33e..5fd6e8ed02b5 100644
> > --- a/net/ipv4/gre_demux.c
> > +++ b/net/ipv4/gre_demux.c
> > @@ -127,7 +127,7 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
> >               if (!pskb_may_pull(skb, nhs + hdr_len + sizeof(*ershdr)))
> >                       return -EINVAL;
> >
> > -             ershdr = (struct erspan_base_hdr *)options;
> > +             ershdr = (struct erspan_base_hdr *)(skb->data + nhs + hdr_len);
>
> It seems to me that in the case of WCCPv2 hdr_len will be 4 bytes longer
> than where options would be advanced to. Is that a problem here?
>

Hi Simon,

I guess the two conditions are mutually exclusive since tpi->proto is
initialized with greh->protocol. Am I missing something?

Regards,
Lorenzo

> >               tpi->key = cpu_to_be32(get_session_id(ershdr));
> >       }
> >
> > --
> > 2.21.0
> >
>

Re: [Patch net] gre: refetch erspan header from skb->data after pskb_may_pull()

[Simon Horman]

On Fri, Dec 06, 2019 at 01:55:25PM +0200, Lorenzo Bianconi wrote:
> >
> > Hi Cong,
> >
> > On Thu, Dec 05, 2019 at 07:39:02PM -0800, Cong Wang wrote:
> > > After pskb_may_pull() we should always refetch the header
> > > pointers from the skb->data in case it got reallocated.
> > >
> > > In gre_parse_header(), the erspan header is still fetched
> > > from the 'options' pointer which is fetched before
> > > pskb_may_pull().
> > >
> > > Found this during code review of a KMSAN bug report.
> > >
> > > Fixes: cb73ee40b1b3 ("net: ip_gre: use erspan key field for tunnel lookup")
> > > Cc: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
> > > Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
> > > ---
> > >  net/ipv4/gre_demux.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/net/ipv4/gre_demux.c b/net/ipv4/gre_demux.c
> > > index 44bfeecac33e..5fd6e8ed02b5 100644
> > > --- a/net/ipv4/gre_demux.c
> > > +++ b/net/ipv4/gre_demux.c
> > > @@ -127,7 +127,7 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
> > >               if (!pskb_may_pull(skb, nhs + hdr_len + sizeof(*ershdr)))
> > >                       return -EINVAL;
> > >
> > > -             ershdr = (struct erspan_base_hdr *)options;
> > > +             ershdr = (struct erspan_base_hdr *)(skb->data + nhs + hdr_len);
> >
> > It seems to me that in the case of WCCPv2 hdr_len will be 4 bytes longer
> > than where options would be advanced to. Is that a problem here?
> >
> 
> Hi Simon,
> 
> I guess the two conditions are mutually exclusive since tpi->proto is
> initialized with greh->protocol. Am I missing something?

Thanks Lorenzo,

I see that now and agree that this patch is correct.

Reviewed-by: Simon Horman <simon.horman@netronome.com>

> > >               tpi->key = cpu_to_be32(get_session_id(ershdr));
> > >       }
> > >
> > > --
> > > 2.21.0
> > >
> >
> 

Re: [Patch net] gre: refetch erspan header from skb->data after pskb_may_pull()

[Lorenzo Bianconi]

>
> After pskb_may_pull() we should always refetch the header
> pointers from the skb->data in case it got reallocated.
>
> In gre_parse_header(), the erspan header is still fetched
> from the 'options' pointer which is fetched before
> pskb_may_pull().
>
> Found this during code review of a KMSAN bug report.
>
> Fixes: cb73ee40b1b3 ("net: ip_gre: use erspan key field for tunnel lookup")
> Cc: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>

Acked-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>

> ---
>  net/ipv4/gre_demux.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/ipv4/gre_demux.c b/net/ipv4/gre_demux.c
> index 44bfeecac33e..5fd6e8ed02b5 100644
> --- a/net/ipv4/gre_demux.c
> +++ b/net/ipv4/gre_demux.c
> @@ -127,7 +127,7 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
>                 if (!pskb_may_pull(skb, nhs + hdr_len + sizeof(*ershdr)))
>                         return -EINVAL;
>
> -               ershdr = (struct erspan_base_hdr *)options;
> +               ershdr = (struct erspan_base_hdr *)(skb->data + nhs + hdr_len);
>                 tpi->key = cpu_to_be32(get_session_id(ershdr));
>         }
>
> --
> 2.21.0
>

Re: [Patch net] gre: refetch erspan header from skb->data after pskb_may_pull()

[William Tu]

On Fri, Dec 6, 2019 at 3:50 AM Lorenzo Bianconi
<lorenzo.bianconi@redhat.com> wrote:
>
> >
> > After pskb_may_pull() we should always refetch the header
> > pointers from the skb->data in case it got reallocated.
> >
> > In gre_parse_header(), the erspan header is still fetched
> > from the 'options' pointer which is fetched before
> > pskb_may_pull().
> >
> > Found this during code review of a KMSAN bug report.
> >
> > Fixes: cb73ee40b1b3 ("net: ip_gre: use erspan key field for tunnel lookup")
> > Cc: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
> > Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
>
> Acked-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
>

LGTM.
Acked-by: William Tu <u9012063@gmail.com>

From the  spec, ERSPAN has fixed size GRE header, so  I think
WCCPv2 should not exist in ERSPAN.

Re: [Patch net] gre: refetch erspan header from skb->data after pskb_may_pull()

[David Miller]

From: Cong Wang <xiyou.wangcong@gmail.com>
Date: Thu,  5 Dec 2019 19:39:02 -0800

> After pskb_may_pull() we should always refetch the header
> pointers from the skb->data in case it got reallocated.
> 
> In gre_parse_header(), the erspan header is still fetched
> from the 'options' pointer which is fetched before
> pskb_may_pull().
> 
> Found this during code review of a KMSAN bug report.
> 
> Fixes: cb73ee40b1b3 ("net: ip_gre: use erspan key field for tunnel lookup")
> Cc: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>

Applied and queued up for -stable, thanks.