net: add a debug check in __skb_push()

Add the following check, to detect bugs sooner for CONFIG_DEBUG_NET=y
builds.

	DEBUG_NET_WARN_ON_ONCE(skb->data < skb->head);

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260130160253.2936789-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index e6bfe5d..8b399dd 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2813,6 +2813,7 @@ static inline void *__skb_push(struct sk_buff *skb, unsigned int len)
        DEBUG_NET_WARN_ON_ONCE(len > INT_MAX);
 
        skb->data -= len;
+       DEBUG_NET_WARN_ON_ONCE(skb->data < skb->head);
        skb->len  += len;
        return skb->data;
 }