[PATCH v2 04/16] skbuff: Phase out ksize() fallback for frag_size

[Kees Cook]

All callers of APIs that allowed a 0-sized frag_size appear to be
passing actual size information already, so this use of ksize() can
be removed. However, just in case there is something still depending
on this behavior, issue a WARN and fall back to as before to ksize()
which means we'll also potentially get KASAN warnings.

Cc: "David S. Miller" <davem at davemloft.net>
Cc: Eric Dumazet <edumazet at google.com>
Cc: Jakub Kicinski <kuba at kernel.org>
Cc: Paolo Abeni <pabeni at redhat.com>
Cc: netdev at vger.kernel.org
Signed-off-by: Kees Cook <keescook at chromium.org>
---
 net/core/skbuff.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 0b30fbdbd0d0..84ca89c781cd 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -195,7 +195,11 @@ static void __build_skb_around(struct sk_buff *skb, void *data,
 			       unsigned int frag_size)
 {
 	struct skb_shared_info *shinfo;
-	unsigned int size = frag_size ? : ksize(data);
+	unsigned int size = frag_size;
+
+	/* All callers should be setting frag size now? */
+	if (WARN_ON_ONCE(size == 0))
+		size = ksize(data);
 
 	size -= SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 
@@ -220,12 +224,10 @@ static void __build_skb_around(struct sk_buff *skb, void *data,
 /**
  * __build_skb - build a network buffer
  * @data: data buffer provided by caller
- * @frag_size: size of data, or 0 if head was kmalloced
+ * @frag_size: size of data
  *
  * Allocate a new &sk_buff. Caller provides space holding head and
- * skb_shared_info. @data must have been allocated by kmalloc() only if
- * @frag_size is 0, otherwise data should come from the page allocator
- *  or vmalloc()
+ * skb_shared_info.
  * The return is the new skb buffer.
  * On a failure the return is %NULL, and @data is not freed.
  * Notes :
@@ -272,7 +274,7 @@ EXPORT_SYMBOL(build_skb);
  * build_skb_around - build a network buffer around provided skb
  * @skb: sk_buff provide by caller, must be memset cleared
  * @data: data buffer provided by caller
- * @frag_size: size of data, or 0 if head was kmalloced
+ * @frag_size: size of data
  */
 struct sk_buff *build_skb_around(struct sk_buff *skb,
 				 void *data, unsigned int frag_size)
@@ -294,7 +296,7 @@ EXPORT_SYMBOL(build_skb_around);
 /**
  * __napi_build_skb - build a network buffer
  * @data: data buffer provided by caller
- * @frag_size: size of data, or 0 if head was kmalloced
+ * @frag_size: size of data
  *
  * Version of __build_skb() that uses NAPI percpu caches to obtain
  * skbuff_head instead of inplace allocation.
@@ -318,7 +320,7 @@ static struct sk_buff *__napi_build_skb(void *data, unsigned int frag_size)
 /**
  * napi_build_skb - build a network buffer
  * @data: data buffer provided by caller
- * @frag_size: size of data, or 0 if head was kmalloced
+ * @frag_size: size of data
  *
  * Version of __napi_build_skb() that takes care of skb->head_frag
  * and skb->pfmemalloc when the data is a page or page fragment.
-- 
2.34.1