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--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -912,6 +912,49 @@ static inline void skb_reserve(struct sk
skb->tail+=len;
}
+/*
+ * CPUs often take a performance hit when accessing unaligned memory
+ * locations. The actual performance hit varies, it can be small if the
+ * hardware handles it or large if we have to take an exception and fix it
+ * in software.
+ *
+ * Since an ethernet header is 14 bytes network drivers often end up with
+ * the IP header at an unaligned offset. The IP header can be aligned by
+ * shifting the start of the packet by 2 bytes. Drivers should do this
+ * with:
+ *
+ * skb_reserve(NET_IP_ALIGN);
+ *
+ * The downside to this alignment of the IP header is that the DMA is now
+ * unaligned. On some architectures the cost of an unaligned DMA is high
+ * and this cost outweighs the gains made by aligning the IP header.
+ *
+ * Since this trade off varies between architectures, we allow NET_IP_ALIGN
+ * to be overridden.
+ */
+#ifndef NET_IP_ALIGN
+#define NET_IP_ALIGN 2
+#endif
+
+/*
+ * The networking layer reserves some headroom in skb data (via
+ * dev_alloc_skb). This is used to avoid having to reallocate skb data when
+ * the header has to grow. In the default case, if the header has to grow
+ * 16 bytes or less we avoid the reallocation.
+ *
+ * Unfortunately this headroom changes the DMA alignment of the resulting
+ * network packet. As for NET_IP_ALIGN, this unaligned DMA is expensive
+ * on some architectures. An architecture can override this value,
+ * perhaps setting it to a cacheline in size (since that will maintain
+ * cacheline alignment of the DMA). It must be a power of 2.
+ *
+ * Various parts of the networking layer expect at least 16 bytes of
+ * headroom, you should not reduce this.
+ */
+#ifndef NET_SKB_PAD
+#define NET_SKB_PAD 16
+#endif
+
extern int ___pskb_trim(struct sk_buff *skb, unsigned int len, int realloc);
static inline void __skb_trim(struct sk_buff *skb, unsigned int len)
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -185,22 +185,31 @@ static __inline__ ssize_t tun_get_user(s
{
struct tun_pi pi = { 0, __constant_htons(ETH_P_IP) };
struct sk_buff *skb;
- size_t len = count;
+ size_t len = count, align = 0;
if (!(tun->flags & TUN_NO_PI)) {
if ((len -= sizeof(pi)) > count)
return -EINVAL;
- memcpy_fromiovec((void *)&pi, iv, sizeof(pi));
+ if(memcpy_fromiovec((void *)&pi, iv, sizeof(pi)))
+ return -EFAULT;
}
-
- if (!(skb = alloc_skb(len + 2, GFP_KERNEL))) {
+
+ if ((tun->flags & TUN_TYPE_MASK) == TUN_TAP_DEV)
+ align = NET_IP_ALIGN;
+
+ if (!(skb = alloc_skb(len + align, GFP_KERNEL))) {
tun->stats.rx_dropped++;
return -ENOMEM;
}
- skb_reserve(skb, 2);
- memcpy_fromiovec(skb_put(skb, len), iv, len);
+ if (align)
+ skb_reserve(skb, align);
+ if (memcpy_fromiovec(skb_put(skb, len), iv, len)) {
+ tun->stats.rx_dropped++;
+ kfree_skb(skb);
+ return -EFAULT;
+ }
skb->dev = &tun->dev;
switch (tun->flags & TUN_TYPE_MASK) {
@@ -271,7 +280,8 @@ static __inline__ ssize_t tun_put_user(s
pi.flags |= TUN_PKT_STRIP;
}
- memcpy_toiovec(iv, (void *) &pi, sizeof(pi));
+ if(memcpy_toiovec(iv, (void *) &pi, sizeof(pi)))
+ return -EFAULT;
total += sizeof(pi);
}
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