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

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

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

Make sure skb_mac_header(), skb_mac_offset() and skb_mac_header_len() uses
are not fooled if the mac header has not been set.

These checks are enabled if CONFIG_DEBUG_NET=y

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

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/linux/skbuff.h | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 82edf0359ab32d0d7cd583676b38d569ce0b24cc..cd4a8268894acce4bde16dc0fedb7eb13706f515 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2763,8 +2763,14 @@ static inline void skb_set_network_header(struct sk_buff *skb, const int offset)
 	skb->network_header += offset;
 }
 
+static inline int skb_mac_header_was_set(const struct sk_buff *skb)
+{
+	return skb->mac_header != (typeof(skb->mac_header))~0U;
+}
+
 static inline unsigned char *skb_mac_header(const struct sk_buff *skb)
 {
+	DEBUG_NET_WARN_ON_ONCE(!skb_mac_header_was_set(skb));
 	return skb->head + skb->mac_header;
 }
 
@@ -2775,14 +2781,10 @@ static inline int skb_mac_offset(const struct sk_buff *skb)
 
 static inline u32 skb_mac_header_len(const struct sk_buff *skb)
 {
+	DEBUG_NET_WARN_ON_ONCE(!skb_mac_header_was_set(skb));
 	return skb->network_header - skb->mac_header;
 }
 
-static inline int skb_mac_header_was_set(const struct sk_buff *skb)
-{
-	return skb->mac_header != (typeof(skb->mac_header))~0U;
-}
-
 static inline void skb_unset_mac_header(struct sk_buff *skb)
 {
 	skb->mac_header = (typeof(skb->mac_header))~0U;
-- 
2.36.1.476.g0c4daa206d-goog

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

[Paolo Abeni]

Hello,

On Mon, 2022-06-20 at 02:30 -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> Make sure skb_mac_header(), skb_mac_offset() and skb_mac_header_len() uses
> are not fooled if the mac header has not been set.
> 
> These checks are enabled if CONFIG_DEBUG_NET=y
> 
> This commit will likely expose existing bugs in linux networking stacks.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> ---
>  include/linux/skbuff.h | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 82edf0359ab32d0d7cd583676b38d569ce0b24cc..cd4a8268894acce4bde16dc0fedb7eb13706f515 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -2763,8 +2763,14 @@ static inline void skb_set_network_header(struct sk_buff *skb, const int offset)
>  	skb->network_header += offset;
>  }
>  
> +static inline int skb_mac_header_was_set(const struct sk_buff *skb)
> +{
> +	return skb->mac_header != (typeof(skb->mac_header))~0U;
> +}
> +
>  static inline unsigned char *skb_mac_header(const struct sk_buff *skb)
>  {
> +	DEBUG_NET_WARN_ON_ONCE(!skb_mac_header_was_set(skb));
>  	return skb->head + skb->mac_header;
>  }
>  
> @@ -2775,14 +2781,10 @@ static inline int skb_mac_offset(const struct sk_buff *skb)
>  
>  static inline u32 skb_mac_header_len(const struct sk_buff *skb)
>  {
> +	DEBUG_NET_WARN_ON_ONCE(!skb_mac_header_was_set(skb));

The patch LGTM. 

I'm wondering if it's worthy adding similar debug checks for network
and transport offset (with more patches). e.g. still in
skb_mac_header_len():

	DEBUG_NET_WARN_ON_ONCE(skb->network_header < skb->mac_header);

Thanks!

Paolo

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

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (master)
by Paolo Abeni <pabeni@redhat.com>:

On Mon, 20 Jun 2022 02:30:17 -0700 you wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> Make sure skb_mac_header(), skb_mac_offset() and skb_mac_header_len() uses
> are not fooled if the mac header has not been set.
> 
> These checks are enabled if CONFIG_DEBUG_NET=y
> 
> [...]

Here is the summary with links:
  - [net-next] net: warn if mac header was not set
    https://git.kernel.org/netdev/net-next/c/f9aefd6b2aa3

You are awesome, thank you!
-- 
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