net: Do not allocate page fragments that are not skb aligned

This patch addresses the fact that there are drivers, specifically tun,
that will call into the network page fragment allocators with buffer sizes
that are not cache aligned. Doing this could result in data alignment
and DMA performance issues as these fragment pools are also shared with the
skb allocator and any other devices that will use napi_alloc_frags or
netdev_alloc_frags.

Fixes: ffde7328 ("net: Split netdev_alloc_frag into __alloc_page_frag and add __napi_alloc_frag")
Reported-by: NJann Horn <jannh@google.com>
Signed-off-by: NAlexander Duyck <alexander.h.duyck@linux.intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -356,6 +356,8 @@ static void *__netdev_alloc_frag(unsigned int fragsz, gfp_t gfp_mask)
  */
 void *netdev_alloc_frag(unsigned int fragsz)
 {
+	fragsz = SKB_DATA_ALIGN(fragsz);
+
 	return __netdev_alloc_frag(fragsz, GFP_ATOMIC);
 }
 EXPORT_SYMBOL(netdev_alloc_frag);
@@ -369,6 +371,8 @@ static void *__napi_alloc_frag(unsigned int fragsz, gfp_t gfp_mask)
 
 void *napi_alloc_frag(unsigned int fragsz)
 {
+	fragsz = SKB_DATA_ALIGN(fragsz);
+
 	return __napi_alloc_frag(fragsz, GFP_ATOMIC);
 }
 EXPORT_SYMBOL(napi_alloc_frag);