linux-kernel - Re: [PATCH net] Revert "net/smc: Introduce TCP ULP support"

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Message-ID: <aXuQ5HoYULzQlFD9@horms.kernel.org>
Date: Thu, 29 Jan 2026 16:55:00 +0000
From: Simon Horman <horms@...nel.org>
To: "D. Wythe" <alibuda@...ux.alibaba.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	Dust Li <dust.li@...ux.alibaba.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Sidraya Jayagond <sidraya@...ux.ibm.com>,
	Wenjia Zhang <wenjia@...ux.ibm.com>,
	Mahanta Jambigi <mjambigi@...ux.ibm.com>,
	Tony Lu <tonylu@...ux.alibaba.com>,
	Wen Gu <guwen@...ux.alibaba.com>, linux-kernel@...r.kernel.org,
	linux-rdma@...r.kernel.org, linux-s390@...r.kernel.org,
	netdev@...r.kernel.org, oliver.yang@...ux.alibaba.com,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH net] Revert "net/smc: Introduce TCP ULP support"

On Wed, Jan 28, 2026 at 01:54:52PM +0800, D. Wythe wrote:
> This reverts commit d7cd421da9da2cc7b4d25b8537f66db5c8331c40.
> 
> As reported by Al Viro, the TCP ULP support for SMC is fundamentally
> broken. The implementation attempts to convert an active TCP socket
> into an SMC socket by modifying the underlying `struct file`, dentry,
> and inode in-place, which violates core VFS invariants that assume
> these structures are immutable for an open file, creating a risk of
> use after free errors and general system instability.
> 
> Given the severity of this design flaw and the fact that cleaner
> alternatives (e.g., LD_PRELOAD, BPF) exist for legacy application
> transparency, the correct course of action is to remove this feature
> entirely.
> 
> Fixes: d7cd421da9da ("net/smc: Introduce TCP ULP support")
> Link: https://lore.kernel.org/netdev/Yus1SycZxcd+wHwz@ZenIV/
> Reported-by: Al Viro <viro@...iv.linux.org.uk>
> Signed-off-by: D. Wythe <alibuda@...ux.alibaba.com>
> Reviewed-by: Tony Lu <tonylu@...ux.alibaba.com>
> Reviewed-by: Dust Li <dust.li@...ux.alibaba.com>

Reviewed-by: Simon Horman <horms@...nel.org>