[RFC 1/1] whitelisting UDP GSO and GRO cmsgs

[Victor Stewart <v@nametag.social>]

add __sys_whitelisted_cmsghdrs() and configure __sys_recvmsg_sock and
__sys_sendmsg_sock to use it.

Signed-off by: Victor Stewart <v@nametag.social>
---
 net/socket.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/net/socket.c b/net/socket.c
index 6e6cccc2104f..44e28bb08bbe 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2416,9 +2416,9 @@ 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 (!__sys_whitelisted_cmsghdrs(msr))
+                       return -EINVAL;

        return ____sys_sendmsg(sock, msg, flags, NULL, 0);
 }
@@ -2620,6 +2620,15 @@ static int ___sys_recvmsg(struct socket *sock,
struct user_msghdr __user *msg,
        return err;
 }

+static bool __sys_whitelisted_cmsghdrs(struct msghdr *msg)
+{
+       for (struct cmsghdr *cmsg = CMSG_FIRSTHDR(msg); cmsg != NULL;
cmsg = CMSG_NXTHDR(message, cmsg))
+               if (cmsg->cmsg_level != SOL_UDP || (cmsg->cmsg_type !=
UDP_GRO && cmsg->cmsg_type != UDP_SEGMENT))
+                       return false;
+
+       return true;
+}
+
 /*
  *     BSD recvmsg interface
  */
@@ -2630,7 +2639,7 @@ long __sys_recvmsg_sock(struct socket *sock,
struct msghdr *msg,
 {
        if (msg->msg_control || msg->msg_controllen) {
                /* disallow ancillary data reqs unless cmsg is plain data */
-               if (!(sock->ops->flags & PROTO_CMSG_DATA_ONLY))
+               if (!( sock->ops->flags & PROTO_CMSG_DATA_ONLY ||
__sys_whitelisted_cmsghdrs(msr) ))
                        return -EINVAL;
        }