[PATCH net-next] net: fix GRO skb truesize update

commit 5e10da5385d2 ("skbuff: allow 'slow_gro' for skb carring sock
reference") introduces a serious regression at the GRO layer setting
the wrong truesize for stolen-head skbs.

Restore the correct truesize: SKB_DATA_ALIGN(...) instead of
SKB_TRUESIZE(...)

Reported-by: Mat Martineau <redacted>
Fixes: 5e10da5385d2 ("skbuff: allow 'slow_gro' for skb carring sock reference")
Signed-off-by: Paolo Abeni <pabeni@redhat.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 97ed77a86bb0..02a603556408 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c

@@ -4375,7 +4375,7 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb)
 		memcpy(frag + 1, skbinfo->frags, sizeof(*frag) * skbinfo->nr_frags);
 		/* We dont need to clear skbinfo->nr_frags here */
 
-		new_truesize = SKB_TRUESIZE(sizeof(struct sk_buff));
+		new_truesize = SKB_DATA_ALIGN(sizeof(struct sk_buff));
 		delta_truesize = skb->truesize - new_truesize;
 		skb->truesize = new_truesize;
 		NAPI_GRO_CB(skb)->free = NAPI_GRO_FREE_STOLEN_HEAD;

-- 
2.26.3

On Wed, 4 Aug 2021, Paolo Abeni wrote:

commit 5e10da5385d2 ("skbuff: allow 'slow_gro' for skb carring sock
reference") introduces a serious regression at the GRO layer setting
the wrong truesize for stolen-head skbs.

Restore the correct truesize: SKB_DATA_ALIGN(...) instead of
SKB_TRUESIZE(...)

Reported-by: Mat Martineau <redacted>
Fixes: 5e10da5385d2 ("skbuff: allow 'slow_gro' for skb carring sock reference")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

With this patch I'm no longer seeing the WARN_ON_ONCE() fire in 
skb_try_coalesce(). Thanks Paolo!

Tested-by: Mat Martineau <redacted>

--
Mat Martineau
Intel

Hello:

This patch was applied to netdev/net-next.git (refs/heads/master):

On Wed,  4 Aug 2021 21:07:00 +0200 you wrote:

commit 5e10da5385d2 ("skbuff: allow 'slow_gro' for skb carring sock
reference") introduces a serious regression at the GRO layer setting
the wrong truesize for stolen-head skbs.

Restore the correct truesize: SKB_DATA_ALIGN(...) instead of
SKB_TRUESIZE(...)

[...]

Here is the summary with links:
  - [net-next] net: fix GRO skb truesize update
    https://git.kernel.org/netdev/net-next/c/af352460b465

You are awesome, thank you!
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