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[82.132.228.95]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-482e28dc10asm3118431f8f.19.2026.08.26.07.36.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 26 Aug 2026 07:36:25 -0700 (PDT) Message-ID: <75cf5a10-f7ae-4b4d-ae47-1556a30d76c9@gmail.com> Date: Wed, 26 Aug 2026 15:36:23 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net 1/1] tcp: reject non zerocopy devmem tx To: Mina Almasry Cc: "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org References: Content-Language: en-US From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 8/23/26 16:58, Mina Almasry wrote: > On Sat, Aug 22, 2026 at 3:57 AM Pavel Begunkov wrote: ...> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c > index b4237d0e994d6..1e34f50770446 100644 > --- a/net/ipv4/tcp.c > +++ b/net/ipv4/tcp.c > @@ -1170,7 +1170,8 @@ int tcp_sendmsg_locked(struct sock *sk, struct > msghdr *msg, size_t size) > } > > if (!sockc_err && sockc.dmabuf_id && > - (!(flags & MSG_ZEROCOPY) || !sock_flag(sk, SOCK_ZEROCOPY))) { > + (!(flags & MSG_ZEROCOPY) || !sock_flag(sk, SOCK_ZEROCOPY) || This check before your diff fells off. From a quick look, via io_uring you can have a sendmsg call with dmabuf_id that would happily pass this check but never goes through net_devmem_get_binding() and msg_zerocopy_realloc(). It's not much too problematic for now but feels dangerous to rely on it in the current form. I think we want sth like this in the end. if (sockc.dmabuf_id && !sockc_err) { if (!binding || zc != MSG_ZEROCOPY) // fail; } > + zc != MSG_ZEROCOPY)) { > err = -EINVAL; > goto out_err; > } > > It will return EINVAL instead of EOPNOTSUPP but I think that is OK. -- Pavel Begunkov