netdev - [PATCH net-next 7/7] net: add debug check in skb_reset_mac

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Message-ID: <20241105174403.850330-8-edumazet@google.com>
Date: Tue,  5 Nov 2024 17:44:03 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 7/7] net: add debug check in skb_reset_mac_header()

Make sure (skb->data - skb->head) can fit in skb->mac_header

This needs CONFIG_DEBUG_NET=y.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/linux/skbuff.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index f1e49a32880df8f3716c585d13c1085a2183978a..e5095d75abba18c5c5301ddc39c40cdcf5e528ed 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3063,7 +3063,10 @@ static inline void skb_unset_mac_header(struct sk_buff *skb)
 
 static inline void skb_reset_mac_header(struct sk_buff *skb)
 {
-	skb->mac_header = skb->data - skb->head;
+	long offset = skb->data - skb->head;
+
+	DEBUG_NET_WARN_ON_ONCE(offset != (typeof(skb->mac_header))offset);
+	skb->mac_header = offset;
 }
 
 static inline void skb_set_mac_header(struct sk_buff *skb, const int offset)
-- 
2.47.0.199.ga7371fff76-goog