[PATCH net-next] net: warn if transport header was not set

[PATCH net-next] net: warn if transport header was not set

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

Make sure skb_transport_header() and skb_transport_offset() uses
are not fooled if the transport header has not been set.

This change will likely expose existing bugs in linux networking stacks.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/linux/skbuff.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index d58669d6cb91aa30edc70d59a0a7e9d4e2298842..043c59fa0bd6d921f2d2e211348929681bfce186 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2804,6 +2804,7 @@ static inline bool skb_transport_header_was_set(const struct sk_buff *skb)
 
 static inline unsigned char *skb_transport_header(const struct sk_buff *skb)
 {
+	WARN_ON_ONCE(!skb_transport_header_was_set(skb));
 	return skb->head + skb->transport_header;
 }
 
-- 
2.36.0.512.ge40c2bad7a-goog

Re: [PATCH net-next] net: warn if transport header was not set

[Jakub Kicinski]

On Mon,  9 May 2022 09:57:16 -0700 Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> Make sure skb_transport_header() and skb_transport_offset() uses
> are not fooled if the transport header has not been set.
> 
> This change will likely expose existing bugs in linux networking stacks.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> ---
>  include/linux/skbuff.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index d58669d6cb91aa30edc70d59a0a7e9d4e2298842..043c59fa0bd6d921f2d2e211348929681bfce186 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -2804,6 +2804,7 @@ static inline bool skb_transport_header_was_set(const struct sk_buff *skb)
>  
>  static inline unsigned char *skb_transport_header(const struct sk_buff *skb)
>  {
> +	WARN_ON_ONCE(!skb_transport_header_was_set(skb));
>  	return skb->head + skb->transport_header;
>  }
>  

This is for prod or for syzbot?

What are your feelings on putting this under a kconfig?

We already have a #ifdef DEBUG in skb_checksum_none_assert()
we could generalize that into some form of kconfig-gated
SKB_CHECK(). Kconfig-gated so that people don't feel self-conscious
about using it. I wrote such a patch a few times already but never 
sent it.

Re: [PATCH net-next] net: warn if transport header was not set

[Eric Dumazet]

On Mon, May 9, 2022 at 10:21 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Mon,  9 May 2022 09:57:16 -0700 Eric Dumazet wrote:
> > From: Eric Dumazet <edumazet@google.com>
> >
> > Make sure skb_transport_header() and skb_transport_offset() uses
> > are not fooled if the transport header has not been set.
> >
> > This change will likely expose existing bugs in linux networking stacks.
> >
> > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > ---
> >  include/linux/skbuff.h | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> > index d58669d6cb91aa30edc70d59a0a7e9d4e2298842..043c59fa0bd6d921f2d2e211348929681bfce186 100644
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -2804,6 +2804,7 @@ static inline bool skb_transport_header_was_set(const struct sk_buff *skb)
> >
> >  static inline unsigned char *skb_transport_header(const struct sk_buff *skb)
> >  {
> > +     WARN_ON_ONCE(!skb_transport_header_was_set(skb));
> >       return skb->head + skb->transport_header;
> >  }
> >
>
> This is for prod or for syzbot?
>
> What are your feelings on putting this under a kconfig?
>
> We already have a #ifdef DEBUG in skb_checksum_none_assert()
> we could generalize that into some form of kconfig-gated
> SKB_CHECK(). Kconfig-gated so that people don't feel self-conscious
> about using it. I wrote such a patch a few times already but never
> sent it.

Sure, we can add a CONFIG_DEBUG_NET, I think it has been suggested in the past.
Then we can ask syzbot teams to turn on this option.

I will send a series with this.