From:   Luiz Augusto von Dentz <luiz.dentz@gmail.com>
To:     davem@davemloft.net, kuba@kernel.org
Cc:     linux-bluetooth@vger.kernel.org, netdev@vger.kernel.org,
        dan.carpenter@oracle.com,
        Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Subject: [PATCH 01/15] skbuff: introduce skb_pull_data
Date:   Tue, 30 Nov 2021 16:02:01 -0800
Message-Id: <20211201000215.1134831-2-luiz.dentz@gmail.com>
In-Reply-To: <20211201000215.1134831-1-luiz.dentz@gmail.com>
References: <20211201000215.1134831-1-luiz.dentz@gmail.com>
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From: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

Like skb_pull but returns the original data pointer before pulling the
data after performing a check against sbk->len.

This allows to change code that does "struct foo *p = (void *)skb->data;"
which is hard to audit and error prone, to:

        p = skb_pull_data(skb, sizeof(*p));
        if (!p)
                return;

Which is both safer and cleaner.

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
 include/linux/skbuff.h |  2 ++
 net/core/skbuff.c      | 23 +++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index eba256af64a5..877dda38684a 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2373,6 +2373,8 @@ static inline void *skb_pull_inline(struct sk_buff *skb, unsigned int len)
 	return unlikely(len > skb->len) ? NULL : __skb_pull(skb, len);
 }
 
+void *skb_pull_data(struct sk_buff *skb, size_t len);
+
 void *__pskb_pull_tail(struct sk_buff *skb, int delta);
 
 static inline void *__pskb_pull(struct sk_buff *skb, unsigned int len)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index a33247fdb8f5..0b19833ffbce 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2023,6 +2023,29 @@ void *skb_pull(struct sk_buff *skb, unsigned int len)
 }
 EXPORT_SYMBOL(skb_pull);
 
+/**
+ *	skb_pull_data - remove data from the start of a buffer returning its
+ *	original position.
+ *	@skb: buffer to use
+ *	@len: amount of data to remove
+ *
+ *	This function removes data from the start of a buffer, returning
+ *	the memory to the headroom. A pointer to the original data in the buffer
+ *	is returned after checking if there is enough data to pull. Once the
+ *	data has been pulled future pushes will overwrite the old data.
+ */
+void *skb_pull_data(struct sk_buff *skb, size_t len)
+{
+	void *data = skb->data;
+
+	if (skb->len < len)
+		return NULL;
+
+	skb_pull(skb, len);
+
+	return data;
+}
+
 /**
  *	skb_trim - remove end from a buffer
  *	@skb: buffer to alter
-- 
2.33.1