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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org Cc: asml.silence@gmail.com, Mina Almasry Subject: [PATCH net v2 1/1] tcp: reject non zerocopy devmem tx Date: Fri, 4 Sep 2026 14:43:07 +0100 Message-ID: X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Devmem tcp tx doesn't work without zero-copy, however it's not currently enforced if NETIF_F_SG isn't present. In this case, tcp_sendmsg_locked() will try the copy path and try to copy data from an iovec which consists of offsets into the dma-buf and would normally fail. Moreover, d9c56501c72fd ("net: tcp: block mixing readable and unreadable frags") relies on that and assumes that the devmem binding is present IFF we're using the zero-copy path, which can be used to mix net-iov and pages in a single skb, and break invariants. Let's reject devmem tx without zero-copy. Note, the parameter check the patch is modifying is too loose, we can create an io_uring request with dmabuf_id and all ZC flags, but which won't have the binding. We replace it with stricter validation. Fixes: bd61848900bff ("net: devmem: Implement TX path") Fixes: d9c56501c72fd ("net: tcp: block mixing readable and unreadable frags") Signed-off-by: Pavel Begunkov --- v2: combine with post ubuf assignment dmabuf_id checks net/ipv4/tcp.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index b4237d0e994d..10f58281be17 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1169,8 +1169,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) zc = MSG_SPLICE_PAGES; } - if (!sockc_err && sockc.dmabuf_id && - (!(flags & MSG_ZEROCOPY) || !sock_flag(sk, SOCK_ZEROCOPY))) { + if (!sockc_err && sockc.dmabuf_id && (zc != MSG_ZEROCOPY || !binding)) { err = -EINVAL; goto out_err; } -- 2.54.0