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>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index eba256a..877dda3 100644 (file)
--- 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 a33247f..dd3ef96 100644 (file)
--- 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