skbuff: introduce skb_pull_data

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.

Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

1 files changed, 24 insertions, 0 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index a33247fdb8f5..dd3ef966efdb 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2024,6 +2024,30 @@ 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;
+}
+EXPORT_SYMBOL(skb_pull_data);
+
+/**
  *	skb_trim - remove end from a buffer
  *	@skb: buffer to alter
  *	@len: new length