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From: Jiayuan Chen <jiayuan.chen@linux.dev>
To: William Bowling <vakzz@zellic.io>, netdev@vger.kernel.org
Cc: "David S . Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Steffen Klassert <steffen.klassert@secunet.com>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	David Ahern <dsahern@kernel.org>
Subject: Re: [PATCH net] net: skbuff: preserve shared-frag marker during coalescing
Date: Thu, 14 May 2026 16:46:49 +0800	[thread overview]
Message-ID: <1707b255-05ac-4d7d-8f06-3c7ac37a23f9@linux.dev> (raw)
In-Reply-To: <20260513041635.1289541-1-vakzz@zellic.io>


On 5/13/26 12:16 PM, William Bowling wrote:
> skb_try_coalesce() can attach paged frags from @from to @to.  If @from
> has SKBFL_SHARED_FRAG set, the resulting @to skb can contain the same
> externally-owned or page-cache-backed frags, but the shared-frag marker
> is currently lost.
>
> That breaks the invariant relied on by later in-place writers.  In
> particular, ESP input checks skb_has_shared_frag() before deciding
> whether an uncloned nonlinear skb can skip skb_cow_data().  If TCP
> receive coalescing has moved shared frags into an unmarked skb, ESP can
> see skb_has_shared_frag() as false and decrypt in place over page-cache
> backed frags.
>
> Propagate SKBFL_SHARED_FRAG when skb_try_coalesce() transfers paged
> frags.  The tailroom copy path does not need the marker because it copies
> bytes into @to's linear data rather than transferring frag descriptors.
>
> Fixes: cef401de7be8 ("net: fix possible wrong checksum generation")
> Fixes: f4c50a4034e6 ("xfrm: esp: avoid in-place decrypt on shared skb frags")

Tested-by: Jiayuan Chen <jiayuan.chen@linux.dev>

I have reproduced and tesed it in 5.15/6.6/upstream with 
https://github.com/v12-security/pocs/tree/main/fragnesia

This patch fixed the issue.

Thanks


  parent reply	other threads:[~2026-05-14  8:47 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-05-13  4:16 [PATCH net] net: skbuff: preserve shared-frag marker during coalescing William Bowling
2026-05-13  8:03 ` Eric Dumazet
2026-05-13 11:31   ` Hyunwoo Kim
2026-05-14  8:46 ` Jiayuan Chen [this message]
2026-05-15  1:00 ` patchwork-bot+netdevbpf

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