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

[Pavel Begunkov <asml.silence@gmail.com>]

On 23/11/2020 15:35, Victor Stewart wrote:
> add __sys_whitelisted_cmsghdrs() and configure __sys_recvmsg_sock and
> __sys_sendmsg_sock to use it.

They haven't been disabled without a reason, and that's not only
because of creds. Did you verify that it's safe to allow those?

> 
> 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))

Its definition below and I don't see a forward declaration anywhere.
Did you even compile this?

> +                       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)

Don't call it __sys*

> +{
> +       for (struct cmsghdr *cmsg = CMSG_FIRSTHDR(msg); cmsg != NULL;
> cmsg = CMSG_NXTHDR(message, cmsg))

no var declarations in for, run checkpatch.pl first

> +               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 ||

extra space after "("

don't forget about brackets when mixing bitwise and logical and/or

It would look better if you'd get rid of outer brackets and propagate ! 

> __sys_whitelisted_cmsghdrs(msr) ))
>                         return -EINVAL;
>         }
> 

-- 
Pavel Begunkov