From 125755776bc6d4dd53eaf551c87e3d460625d638 Mon Sep 17 00:00:00 2001 From: Pavel Begunkov Date: Fri, 4 Sep 2026 14:43:07 +0100 Subject: [PATCH] tcp: reject non zerocopy devmem tx 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 Reviewed-by: Mina Almasry Link: https://patch.msgid.link/fdc2478d8f21268d7078556409887d8e6ba0ad32.1788529053.git.asml.silence@gmail.com Signed-off-by: Paolo Abeni --- 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 1c867a302444..562752352afe 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; }