net: add debug check in skb_reset_inner_mac_header()

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

This needs CONFIG_DEBUG_NET=y.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Joe Damato <jdamato@fastly.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Link: https://patch.msgid.link/20241105174403.850330-5-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 8dafd1295a6e921e9fba69b730286ea28fdc5249..32a7d8a65b9f8f6087007177e763dc9498215e34 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2982,7 +2982,10 @@ static inline unsigned char *skb_inner_mac_header(const struct sk_buff *skb)
 
 static inline void skb_reset_inner_mac_header(struct sk_buff *skb)
 {
-       skb->inner_mac_header = skb->data - skb->head;
+       long offset = skb->data - skb->head;
+
+       DEBUG_NET_WARN_ON_ONCE(offset != (typeof(skb->inner_mac_header))offset);
+       skb->inner_mac_header = offset;
 }
 
 static inline void skb_set_inner_mac_header(struct sk_buff *skb,