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[82.132.212.67]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c20f0d30dafsm92165866b.2.2026.08.12.06.37.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 12 Aug 2026 06:37:47 -0700 (PDT) Message-ID: <4f0685a2-562e-4b63-a6f8-9522ed5ff793@gmail.com> Date: Wed, 12 Aug 2026 14:37:38 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net v3 2/2] net: tcp: block standard payload injection into devmem skbs To: Eric Dumazet , Mina Almasry Cc: Jakub Kicinski , Willem de Bruijn , Kaiyuan Zhang , Stanislav Fomichev , Paolo Abeni , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, dev@openvswitch.org, "David S. Miller" , Simon Horman , Neal Cardwell , Kuniyuki Iwashima , Aaron Conole , Eelco Chaudron , Ilya Maximets , Jason Xing , Bobby Eshleman , Florian Westphal , Bobby Eshleman References: <20260811195405.3979177-1-almasrymina@google.com> <20260811195405.3979177-2-almasrymina@google.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 8/12/26 13:01, Eric Dumazet wrote: > On Tue, Aug 11, 2026 at 9:54 PM Mina Almasry wrote: >> >> Protect tcp_sendmsg_locked() from mistakenly appending non-zerocopy >> page fragments to unreadable devmem skbs. Create a new segment instead. >> >> Fixes: bd61848900bff ("net: devmem: Implement TX path") >> Cc: Pavel Begunkov >> Cc: Stanislav Fomichev >> Cc: Bobby Eshleman >> Reviewed-by: Pavel Begunkov >> Reviewed-by: Bobby Eshleman >> Signed-off-by: Mina Almasry >> --- >> net/ipv4/tcp.c | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c >> index 455441f1b6949..186a36c698798 100644 >> --- a/net/ipv4/tcp.c >> +++ b/net/ipv4/tcp.c >> @@ -1278,6 +1278,11 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) >> if (copy > msg_data_left(msg)) >> copy = msg_data_left(msg); >> >> + if (zc != MSG_ZEROCOPY && unlikely(!skb_frags_readable(skb))) { > > This seems wrong, as @binding could be NULL or not ? I'd say it is *supposed* to be null as device memory without zero copy doesn't make sense, but it looks like that can happen if there is no NETIF_F_SG. How about rejecting it? It'd EFAULT somewhere in skb_copy_to_page_nocache() anyway. diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 455441f1b694..f403830af65f 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1162,6 +1162,10 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) binding = NULL; goto out_err; } + if (zc != MSG_ZEROCOPY) { + err = -EOPNOTSUPP; + goto out_err; + } } } } else if (unlikely(msg->msg_flags & MSG_SPLICE_PAGES) && size) { > Also testing the condition right after a fresh skb was allocated is > adding unecessary cost. FWIW, we can even remove all extra overhead with a new SKBFL flag and checking it together with likes of skb_zcopy_pure(), but IMHO it's better to be done on top if needed. -- Pavel Begunkov