Re: [PATCH bpf 1/2] xsk: fix to reject invalid flags in xsk_bind

[Maciej Fijalkowski <maciejromanfijalkowski@gmail.com>]

On Fri,  8 Mar 2019 08:57:26 +0100
Björn Töpel <bjorn.topel@gmail.com> wrote:

> From: Björn Töpel <bjorn.topel@intel.com>
> 
> Passing a non-existing flag in the sxdp_flags member of struct
> sockaddr_xdp was, incorrectly, silently ignored. This patch addresses
> that behavior, and rejects any non-existing flags.
> 
> We have examined existing user space code, and to our best knowledge,
> no one is relying on the current incorrect behavior. AF_XDP is still
> in its infancy, so from our perspective, the risk of breakage is very
> low, and addressing this problem now is important.
> 
> Fixes: 965a99098443 ("xsk: add support for bind for Rx")
> Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
> ---
>  net/xdp/xsk.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index 6697084e3fdf..a14e8864e4fa 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -407,6 +407,10 @@ static int xsk_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
>  	if (sxdp->sxdp_family != AF_XDP)
>  		return -EINVAL;
>  
> +	flags = sxdp->sxdp_flags;
> +	if (flags & ~(XDP_SHARED_UMEM | XDP_COPY | XDP_ZEROCOPY))
> +		return -EINVAL;
> +

What about setting more than one flag at a time? Is it allowed/make any sense?
After a quick look it seems that they exclude each other, e.g. you can't force
a zero copy and copy mode at the same time. And for XDP_SHARED_UMEM two
remaining flags can't be set.

So maybe check here also that only one particular flag is set by doing:

if (hweight32(flags & (XDP_SHARED_UMEM | XDP_COPY | XDP_ZEROCOPY)) > 1)
	return -EINVAL;

just like we do it for IFLA_XDP_FLAGS in net/core/rtnetlink.c?

>  	mutex_lock(&xs->mutex);
>  	if (xs->dev) {
>  		err = -EBUSY;
> @@ -425,7 +429,6 @@ static int xsk_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
>  	}
>  
>  	qid = sxdp->sxdp_queue_id;
> -	flags = sxdp->sxdp_flags;
>  
>  	if (flags & XDP_SHARED_UMEM) {
>  		struct xdp_sock *umem_xs;