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

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Message-Id: <20220620093017.3366713-1-eric.dumazet@gmail.com>
Date:   Mon, 20 Jun 2022 02:30:17 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH net-next] net: warn if mac header was not set

From: Eric Dumazet <edumazet@...gle.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@...gle.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