Re: [PATCH] net: don't unconditionally copy_from_user a struct ifreq for socket ioctls

On Thu, Aug 26, 2021 at 1:59 AM Arnd Bergmann [off-list ref] wrote:

On Thu, Aug 26, 2021 at 3:28 AM Peter Collingbourne [off-list ref] wrote:

quoted

-       } else {
+       } else if (is_dev_ioctl_cmd(cmd)) {
                struct ifreq ifr;
                bool need_copyout;
                if (copy_from_user(&ifr, argp, sizeof(struct ifreq)))

@@ -1118,6 +1118,8 @@ static long sock_do_ioctl(struct net *net, struct socket *sock,
                if (!err && need_copyout)
                        if (copy_to_user(argp, &ifr, sizeof(struct ifreq)))
                                return -EFAULT;
+       } else {
+               err = -ENOTTY;
        }
        return err;
 }

@@ -3306,6 +3308,8 @@ static int compat_ifr_data_ioctl(struct net *net, unsigned int cmd,
        struct ifreq ifreq;
        u32 data32;

+       if (!is_dev_ioctl_cmd(cmd))
+               return -ENOTTY;
        if (copy_from_user(ifreq.ifr_name, u_ifreq32->ifr_name, IFNAMSIZ))
                return -EFAULT;
        if (get_user(data32, &u_ifreq32->ifr_data))

This adds yet another long switch() statement into the socket ioctl
case, when there
is already one in compat_sock_ioctl_trans(), one in dev_ifsioc() and one in
dev_ioctl(), all with roughly the same set of ioctl command codes. If

I think that David's suggestion of using _IOC_TYPE() should be enough
to address this for now.

any of them
are called frequently, that makes it all even slower, so I wonder if
there should
be a larger rework altogether. Maybe something based on a single lookup table
that we search through directly from sock_ioctl()/compat_sock_ioctl() to deal
with the differences in handling (ifreq based, compat handler, proto_ops
override, dev_load, rtnl_lock, rcu_read_lock, CAP_NET_ADMIN, copyout, ...).

You are also adding the checks into different places for native and compat
mode, which makes them diverge more when we should be trying to
make them more common.

I think based on my recent changes, some other simplifications are possible,
based on how the compat path already enumerates all the dev ioctls.

I think we should leave that for a followup if still necessary.

Peter