[PATCH 1/3] add PROTO_CMSG_DATA_ONLY to __sys_sendmsg_sock

[Victor Stewart <v@nametag.social>]

add PROTO_CMSG_DATA_ONLY whitelisting to __sys_sendmsg_sock

Signed-off by: Victor Stewart <v@nametag.social>
---
 net/socket.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/socket.c b/net/socket.c
index 6e6cccc2104f..6995835d6355 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2416,9 +2416,11 @@ static int ___sys_sendmsg(struct socket *sock,
struct user_msghdr __user *msg,
 long __sys_sendmsg_sock(struct socket *sock, struct msghdr *msg,
                        unsigned int flags)
 {
-       /* disallow ancillary data requests from this path */
-       if (msg->msg_control || msg->msg_controllen)
-               return -EINVAL;
+       if (msg->msg_control || msg->msg_controllen) {
+               /* disallow ancillary data reqs unless cmsg is plain data */
+               if (!(sock->ops->flags & PROTO_CMSG_DATA_ONLY))
+                       return -EINVAL;
+       }

        return ____sys_sendmsg(sock, msg, flags, NULL, 0);
 }