gso: handle new frag_list of frags GRO packets

Recently GRO started generating packets with frag_lists of frags.
This was not handled by GSO, thus leading to a crash.

Thankfully these packets are of a regular form and are easy to
handle.  This patch handles them in two ways.  For completely
non-linear frag_list entries, we simply continue to iterate over
the frag_list frags once we exhaust the normal frags.  For frag_list
entries with linear parts, we call pskb_trim on the first part
of the frag_list skb, and then process the rest of the frags in
the usual way.

This patch also kills a chunk of dead frag_list code that has
obviously never ever been run since it ends up generating a bogus
GSO-segmented packet with a frag_list entry.

Future work is planned to split super big packets into TSO
ones.

Fixes: 8a29111c7ca6 ("net: gro: allow to build full sized skb")
Reported-by: Christoph Paasch <christoph.paasch@uclouvain.be>
Reported-by: Jerry Chu <hkchu@google.com>
Reported-by: Sander Eikelenboom <linux@eikelenboom.it>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Sander Eikelenboom <linux@eikelenboom.it>
Tested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 50 insertions, 25 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 8cec1e6b844d..2718fed53d8c 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2796,6 +2796,7 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
         struct sk_buff *segs = NULL;
         struct sk_buff *tail = NULL;
         struct sk_buff *fskb = skb_shinfo(skb)->frag_list;
+        skb_frag_t *skb_frag = skb_shinfo(skb)->frags;
         unsigned int mss = skb_shinfo(skb)->gso_size;
         unsigned int doffset = skb->data - skb_mac_header(skb);
         unsigned int offset = doffset;
@@ -2835,16 +2836,38 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
                 if (hsize > len || !sg)
                         hsize = len;
 
-                if (!hsize && i >= nfrags) {
-                        BUG_ON(fskb->len != len);
+                if (!hsize && i >= nfrags && skb_headlen(fskb) &&
+                    (skb_headlen(fskb) == len || sg)) {
+                        BUG_ON(skb_headlen(fskb) > len);
+
+                        i = 0;
+                        nfrags = skb_shinfo(fskb)->nr_frags;
+                        skb_frag = skb_shinfo(fskb)->frags;
+                        pos += skb_headlen(fskb);
+
+                        while (pos < offset + len) {
+                                BUG_ON(i >= nfrags);
+
+                                size = skb_frag_size(skb_frag);
+                                if (pos + size > offset + len)
+                                        break;
+
+                                i++;
+                                pos += size;
+                                skb_frag++;
+                        }
 
-                        pos += len;
                         nskb = skb_clone(fskb, GFP_ATOMIC);
                         fskb = fskb->next;
 
                         if (unlikely(!nskb))
                                 goto err;
 
+                        if (unlikely(pskb_trim(nskb, len))) {
+                                kfree_skb(nskb);
+                                goto err;
+                        }
+
                         hsize = skb_end_offset(nskb);
                         if (skb_cow_head(nskb, doffset + headroom)) {
                                 kfree_skb(nskb);
@@ -2881,7 +2904,7 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
                                                  nskb->data - tnl_hlen,
                                                  doffset + tnl_hlen);
 
-                if (fskb != skb_shinfo(skb)->frag_list)
+                if (nskb->len == len + doffset)
                         goto perform_csum_check;
 
                 if (!sg) {
@@ -2899,8 +2922,28 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
 
                 skb_shinfo(nskb)->tx_flags = skb_shinfo(skb)->tx_flags & SKBTX_SHARED_FRAG;
 
-                while (pos < offset + len && i < nfrags) {
-                        *frag = skb_shinfo(skb)->frags[i];
+                while (pos < offset + len) {
+                        if (i >= nfrags) {
+                                BUG_ON(skb_headlen(fskb));
+
+                                i = 0;
+                                nfrags = skb_shinfo(fskb)->nr_frags;
+                                skb_frag = skb_shinfo(fskb)->frags;
+
+                                BUG_ON(!nfrags);
+
+                                fskb = fskb->next;
+                        }
+
+                        if (unlikely(skb_shinfo(nskb)->nr_frags >=
+                                     MAX_SKB_FRAGS)) {
+                                net_warn_ratelimited(
+                                        "skb_segment: too many frags: %u %u\n",
+                                        pos, mss);
+                                goto err;
+                        }
+
+                        *frag = *skb_frag;
                         __skb_frag_ref(frag);
                         size = skb_frag_size(frag);
 
@@ -2913,6 +2956,7 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
 
                         if (pos + size <= offset + len) {
                                 i++;
+                                skb_frag++;
                                 pos += size;
                         } else {
                                 skb_frag_size_sub(frag, pos + size - (offset + len));
@@ -2922,25 +2966,6 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
                         frag++;
                 }
 
-                if (pos < offset + len) {
-                        struct sk_buff *fskb2 = fskb;
-
-                        BUG_ON(pos + fskb->len != offset + len);
-
-                        pos += fskb->len;
-                        fskb = fskb->next;
-
-                        if (fskb2->next) {
-                                fskb2 = skb_clone(fskb2, GFP_ATOMIC);
-                                if (!fskb2)
-                                        goto err;
-                        } else
-                                skb_get(fskb2);
-
-                        SKB_FRAG_ASSERT(nskb);
-                        skb_shinfo(nskb)->frag_list = fskb2;
-                }
-
 skip_fraglist:
                 nskb->data_len = len - hsize;
                 nskb->len += nskb->data_len;