net: add debug check in skb_reset_transport_header()

Make sure (skb->data - skb->head) can fit in skb->transport_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/20241105174403.850330-6-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 32a7d8a65b9f8f6087007177e763dc9498215e34..f76524844e7edc5fe4e0afc27ce71eed7fbd40f9 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3007,7 +3007,10 @@ static inline unsigned char *skb_transport_header(const struct sk_buff *skb)
 
 static inline void skb_reset_transport_header(struct sk_buff *skb)
 {
-       skb->transport_header = skb->data - skb->head;
+       long offset = skb->data - skb->head;
+
+       DEBUG_NET_WARN_ON_ONCE(offset != (typeof(skb->transport_header))offset);
+       skb->transport_header = offset;
 }
 
 static inline void skb_set_transport_header(struct sk_buff *skb,