linux-kernel - [PATCH 4.9 24/54] gso: Validate assumption of frag

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Message-Id: <20170501212632.745131758@linuxfoundation.org>
Date:   Mon,  1 May 2017 14:31:31 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ilan Tayari <ilant@...lanox.com>,
        Ilya Lesokhin <ilyal@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.9 24/54] gso: Validate assumption of frag_list segementation

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ilan Tayari <ilant@...lanox.com>


[ 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@...lanox.com>
Signed-off-by: Ilya Lesokhin <ilyal@...lanox.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/core/skbuff.c |   18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3076,22 +3076,32 @@ struct sk_buff *skb_segment(struct sk_bu
 	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