ipsec: ipcomp - Decompress into frags if necessary

When decompressing extremely large packets allocating them through
kmalloc is prone to failure.  Therefore it's better to use page
frags instead.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 42 insertions, 6 deletions

diff --git a/net/xfrm/xfrm_ipcomp.c b/net/xfrm/xfrm_ipcomp.c
index b51e804fbbad..800f669083fb 100644
--- a/net/xfrm/xfrm_ipcomp.c
+++ b/net/xfrm/xfrm_ipcomp.c
@@ -17,6 +17,7 @@
 
 #include <linux/crypto.h>
 #include <linux/err.h>
+#include <linux/gfp.h>
 #include <linux/list.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
@@ -49,6 +50,7 @@ static int ipcomp_decompress(struct xfrm_state *x, struct sk_buff *skb)
         u8 *scratch = *per_cpu_ptr(ipcomp_scratches, cpu);
         struct crypto_comp *tfm = *per_cpu_ptr(ipcd->tfms, cpu);
         int err = crypto_comp_decompress(tfm, start, plen, scratch, &dlen);
+        int len;
 
         if (err)
                 goto out;
@@ -58,13 +60,47 @@ static int ipcomp_decompress(struct xfrm_state *x, struct sk_buff *skb)
                 goto out;
         }
 
-        err = pskb_expand_head(skb, 0, dlen - plen, GFP_ATOMIC);
-        if (err)
-                goto out;
+        len = dlen - plen;
+        if (len > skb_tailroom(skb))
+                len = skb_tailroom(skb);
+
+        skb->truesize += len;
+        __skb_put(skb, len);
+
+        len += plen;
+        skb_copy_to_linear_data(skb, scratch, len);
+
+        while ((scratch += len, dlen -= len) > 0) {
+                skb_frag_t *frag;
+
+                err = -EMSGSIZE;
+                if (WARN_ON(skb_shinfo(skb)->nr_frags >= MAX_SKB_FRAGS))
+                        goto out;
+
+                frag = skb_shinfo(skb)->frags + skb_shinfo(skb)->nr_frags;
+                frag->page = alloc_page(GFP_ATOMIC);
+
+                err = -ENOMEM;
+                if (!frag->page)
+                        goto out;
+
+                len = PAGE_SIZE;
+                if (dlen < len)
+                        len = dlen;
+
+                memcpy(page_address(frag->page), scratch, len);
+
+                frag->page_offset = 0;
+                frag->size = len;
+                skb->truesize += len;
+                skb->data_len += len;
+                skb->len += len;
+
+                skb_shinfo(skb)->nr_frags++;
+        }
+
+        err = 0;
 
-        skb->truesize += dlen - plen;
-        __skb_put(skb, dlen - plen);
-        skb_copy_to_linear_data(skb, scratch, dlen);
 out:
         put_cpu();
         return err;