netdev - [PATCH net] gve: fix frag

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Message-ID: <20230831213812.3042540-1-edumazet@google.com>
Date: Thu, 31 Aug 2023 21:38:12 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>, Bailey Forrest <bcf@...gle.com>, 
	Willem de Bruijn <willemb@...gle.com>, Catherine Sullivan <csully@...gle.com>
Subject: [PATCH net] gve: fix frag_list chaining

gve_rx_append_frags() is able to build skbs chained with frag_list,
like GRO engine.

Problem is that shinfo->frag_list should only be used
for the head of the chain.

All other links should use skb->next pointer.

Otherwise, built skbs are not valid and can cause crashes.

Equivalent code in GRO (skb_gro_receive()) is:

    if (NAPI_GRO_CB(p)->last == p)
        skb_shinfo(p)->frag_list = skb;
    else
        NAPI_GRO_CB(p)->last->next = skb;
    NAPI_GRO_CB(p)->last = skb;

Fixes: 9b8dd5e5ea48 ("gve: DQO: Add RX path")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Bailey Forrest <bcf@...gle.com>
Cc: Willem de Bruijn <willemb@...gle.com>
Cc: Catherine Sullivan <csully@...gle.com>
---
 drivers/net/ethernet/google/gve/gve_rx_dqo.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/google/gve/gve_rx_dqo.c b/drivers/net/ethernet/google/gve/gve_rx_dqo.c
index ea0e38b4d9e9f6c41441729d6ae5693186f03040..f281e42a7ef9680e2049a185782a37d402c7f886 100644
--- a/drivers/net/ethernet/google/gve/gve_rx_dqo.c
+++ b/drivers/net/ethernet/google/gve/gve_rx_dqo.c
@@ -570,7 +570,10 @@ static int gve_rx_append_frags(struct napi_struct *napi,
 		if (!skb)
 			return -1;
 
-		skb_shinfo(rx->ctx.skb_tail)->frag_list = skb;
+		if (rx->ctx.skb_tail == rx->ctx.skb_head)
+			skb_shinfo(rx->ctx.skb_head)->frag_list = skb;
+		else
+			rx->ctx.skb_tail->next = skb;
 		rx->ctx.skb_tail = skb;
 		num_frags = 0;
 	}
-- 
2.42.0.283.g2d96d420d3-goog