tcp: reject non zerocopy devmem tx

[ Upstream commit 125755776bc6d4dd53eaf551c87e3d460625d638 ]

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 <asml.silence@gmail.com>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Link: https://patch.msgid.link/fdc2478d8f21268d7078556409887d8e6ba0ad32.1788529053.git.asml.silence@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 02f5d53245547762ea417a5869a63824c231110a..53700d6f6f2802d0e1fd04b406a1e0761d2565ec 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1132,8 +1132,7 @@ 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;
        }