netdev - [PATCH] net:fix up skbs delta_truesize in UDP GRO frag

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Message-ID: <1645767824-6899-1-git-send-email-lena.wang@mediatek.com>
Date:   Fri, 25 Feb 2022 13:43:43 +0800
From:   Lena Wang <lena.wang@...iatek.com>
To:     <davem@...emloft.net>, <kuba@...nel.org>, <matthias.bgg@...il.com>
CC:     <wsd_upstream@...iatek.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <lena.wang@...iatek.com>,
        <hao.lin@...iatek.com>
Subject: [PATCH] net:fix up skbs delta_truesize in UDP GRO frag_list

From: lena wang <lena.wang@...iatek.com>

The truesize for a UDP GRO packet is added by main skb and skbs in main
skb's frag_list:
skb_gro_receive_list
        p->truesize += skb->truesize;

When uncloning skb, it will call pskb_expand_head and trusesize for
frag_list skbs may increase. This can occur when allocators uses
__netdev_alloc_skb and not jump into __alloc_skb. This flow does not
use ksize(len) to calculate truesize while pskb_expand_head uses.
skb_segment_list
err = skb_unclone(nskb, GFP_ATOMIC);
pskb_expand_head
        if (!skb->sk || skb->destructor == sock_edemux)
                skb->truesize += size - osize;

If we uses increased truesize adding as delta_truesize, it will be
larger than before and even larger than previous total truesize value
if skbs in frag_list are abundant. The main skb truesize will become
smaller and even a minus value or a huge value for an unsigned int
parameter. Then the following memory check will drop this abnormal skb.

To avoid this error we should use the original truesize to segment the
main skb.

Signed-off-by: lena wang <lena.wang@...iatek.com>
---
 net/core/skbuff.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 9d0388be..8b7356c 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3876,6 +3876,7 @@ struct sk_buff *skb_segment_list(struct sk_buff *skb,
 		list_skb = list_skb->next;
 
 		err = 0;
+		delta_truesize += nskb->truesize;
 		if (skb_shared(nskb)) {
 			tmp = skb_clone(nskb, GFP_ATOMIC);
 			if (tmp) {
@@ -3900,7 +3901,6 @@ struct sk_buff *skb_segment_list(struct sk_buff *skb,
 		tail = nskb;
 
 		delta_len += nskb->len;
-		delta_truesize += nskb->truesize;
 
 		skb_push(nskb, -skb_network_offset(nskb) + offset);
 
-- 
1.9.1