From: Eric Dumazet <edumazet@google.com>
Date: Thu, 2 Jun 2022 16:18:58 +0000 (-0700)
Subject: net: add debug info to __skb_pull()
X-Git-Tag: baikal/aarch64/sdk6.1~3836^2^2~1
X-Git-Url: https://git.baikalelectronics.ru/sdk/?a=commitdiff_plain;h=5a8d94ef5e341bfcdaf0a3fb41cb05d5da7d5205;p=kernel.git

net: add debug info to __skb_pull()

While analyzing yet another syzbot report, I found the following
patch very useful. It allows to better understand what went wrong.

This debug info is only enabled if CONFIG_DEBUG_NET=y,
which is the case for syzbot builds.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index da96f0d3e753f..d3d10556f0fae 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2696,7 +2696,14 @@ void *skb_pull(struct sk_buff *skb, unsigned int len);
 static inline void *__skb_pull(struct sk_buff *skb, unsigned int len)
 {
 	skb->len -= len;
-	BUG_ON(skb->len < skb->data_len);
+	if (unlikely(skb->len < skb->data_len)) {
+#if defined(CONFIG_DEBUG_NET)
+		skb->len += len;
+		pr_err("__skb_pull(len=%u)\n", len);
+		skb_dump(KERN_ERR, skb, false);
+#endif
+		BUG();
+	}
 	return skb->data += len;
 }