gso: Validate assumption of frag_list segementation

[ Upstream commit 43170c4e0ba709c79130c3fe5a41e66279950cd0 ]

Commit 07b26c9454a2 ("gso: Support partial splitting at the frag_list
pointer") assumes that all SKBs in a frag_list (except maybe the last
one) contain the same amount of GSO payload.

This assumption is not always correct, resulting in the following
warning message in the log:
    skb_segment: too many frags

For example, mlx5 driver in Striding RQ mode creates some RX SKBs with
one frag, and some with 2 frags.
After GRO, the frag_list SKBs end up having different amounts of payload.
If this frag_list SKB is then forwarded, the aforementioned assumption
is violated.

Validate the assumption, and fall back to software GSO if it not true.

Change-Id: Ia03983f4a47b6534dd987d7a2aad96d54d46d212
Fixes: 07b26c9454a2 ("gso: Support partial splitting at the frag_list pointer")
Signed-off-by: Ilan Tayari <ilant@mellanox.com>
Signed-off-by: Ilya Lesokhin <ilyal@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 14 insertions, 4 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 5ec34eae3f0a..fe008f1bd930 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3076,22 +3076,32 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
         if (sg && csum && (mss != GSO_BY_FRAGS))  {
                 if (!(features & NETIF_F_GSO_PARTIAL)) {
                         struct sk_buff *iter;
+                        unsigned int frag_len;
 
                         if (!list_skb ||
                             !net_gso_ok(features, skb_shinfo(head_skb)->gso_type))
                                 goto normal;
 
-                        /* Split the buffer at the frag_list pointer.
-                         * This is based on the assumption that all
-                         * buffers in the chain excluding the last
-                         * containing the same amount of data.
+                        /* If we get here then all the required
+                         * GSO features except frag_list are supported.
+                         * Try to split the SKB to multiple GSO SKBs
+                         * with no frag_list.
+                         * Currently we can do that only when the buffers don't
+                         * have a linear part and all the buffers except
+                         * the last are of the same length.
                          */
+                        frag_len = list_skb->len;
                         skb_walk_frags(head_skb, iter) {
+                                if (frag_len != iter->len && iter->next)
+                                        goto normal;
                                 if (skb_headlen(iter))
                                         goto normal;
 
                                 len -= iter->len;
                         }
+
+                        if (len != frag_len)
+                                goto normal;
                 }
 
                 /* GSO partial only requires that we trim off any excess that