Re: [PATCH v2 net] netlink: Use copy_to_user() for optval in netlink_getsockopt().

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From:   Jakub Kicinski <kuba@kernel.org>
Date:   Thu, 20 Apr 2023 20:33:24 -0700
> On Thu, 20 Apr 2023 16:33:51 -0700 Kuniyuki Iwashima wrote:
> > diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> > index f365dfdd672d..5c0d17b3984c 100644
> > --- a/net/netlink/af_netlink.c
> > +++ b/net/netlink/af_netlink.c
> > @@ -1742,7 +1742,7 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
> >  {
> >  	struct sock *sk = sock->sk;
> >  	struct netlink_sock *nlk = nlk_sk(sk);
> > -	int len, val, err;
> > +	int len, val;
> >  
> >  	if (level != SOL_NETLINK)
> >  		return -ENOPROTOOPT;
> > @@ -1753,40 +1753,27 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
> >  		return -EINVAL;
> >  
> >  	switch (optname) {
> > -	case NETLINK_PKTINFO:
> > +	case NETLINK_LIST_MEMBERSHIPS:
> > +		break;
> > +	default:
> >  		if (len < sizeof(int))
> >  			return -EINVAL;
> >  		len = sizeof(int);
> > +	}
> 
> 
> > -		err = 0;
> >  		break;
> >  	default:
> > -		err = -ENOPROTOOPT;
> > +		return -ENOPROTOOPT;
> >  	}
> > -	return err;
> > +
> > +	if (put_user(len, optlen) ||
> > +	    copy_to_user(optval, &val, len))
> > +		return -EFAULT;
> 
> Maybe this is a nit pick but we'd unnecessarily change the return value
> to unknown opts when len < 4, from -ENOPROTOOPT to -EINVAL, right?

Exactly, we should not change it.

> 
> How about we do:

This is cleaner, will do in v3.

Thanks!

> 
> 	unsigned int flag;
> 
> 	flag = 0;
> 	switch (optname) {
> 	case NETLINK_PKTINFO:
> 		flag = NETLINK_F_RECV_PKTINFO;
>  		break;
>  	case NETLINK_BROADCAST_ERROR:
> 		flag = NETLINK_F_BROADCAST_SEND_ERROR;
> 		break;
> 	...
> 	case NETLINK_LIST_MEMBERSHIPS: {
> 	...
> 	default:
> 		return -ENOPROTOOPT;
> 	}
> 
> 	if (flag) {
> 		if (len < sizeof(int))
> 			return -EINVAL;
> 		len = sizeof(int);
>  		val = nlk->flags & flag ? 1 : 0;
> 		if (put_user(len, optlen) || 
> 		    copy_to_user(optval, &val, len))
> 			return -EFAULT;
> 		...
> 	}