[PATCH 01/15] skbuff: introduce skb_pull_data

Luiz Augusto von Dentz
2021-12-01T00:03:05Z

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