Re: [PATCH v2] netfilter: xt_owner: Add supplementary groups option

[Eric Dumazet]

On 5/8/19 10:12 AM, Lukasz Pawelczyk wrote:
> The XT_SUPPL_GROUPS flag causes GIDs specified with XT_OWNER_GID to
> be also checked in the supplementary groups of a process.
> 
> Signed-off-by: Lukasz Pawelczyk <l.pawelczyk@xxxxxxxxxxx>
> ---
>  include/uapi/linux/netfilter/xt_owner.h |  1 +
>  net/netfilter/xt_owner.c                | 23 ++++++++++++++++++++---
>  2 files changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/include/uapi/linux/netfilter/xt_owner.h b/include/uapi/linux/netfilter/xt_owner.h
> index fa3ad84957d5..d646f0dc3466 100644
> --- a/include/uapi/linux/netfilter/xt_owner.h
> +++ b/include/uapi/linux/netfilter/xt_owner.h
> @@ -8,6 +8,7 @@ enum {
>  	XT_OWNER_UID    = 1 << 0,
>  	XT_OWNER_GID    = 1 << 1,
>  	XT_OWNER_SOCKET = 1 << 2,
> +	XT_SUPPL_GROUPS = 1 << 3,
>  };
>  
>  struct xt_owner_match_info {
> diff --git a/net/netfilter/xt_owner.c b/net/netfilter/xt_owner.c
> index 46686fb73784..283a1fb5cc52 100644
> --- a/net/netfilter/xt_owner.c
> +++ b/net/netfilter/xt_owner.c
> @@ -91,11 +91,28 @@ owner_mt(const struct sk_buff *skb, struct xt_action_param *par)
>  	}
>  
>  	if (info->match & XT_OWNER_GID) {
> +		unsigned int i, match = false;
>  		kgid_t gid_min = make_kgid(net->user_ns, info->gid_min);
>  		kgid_t gid_max = make_kgid(net->user_ns, info->gid_max);
> -		if ((gid_gte(filp->f_cred->fsgid, gid_min) &&
> -		     gid_lte(filp->f_cred->fsgid, gid_max)) ^
> -		    !(info->invert & XT_OWNER_GID))
> +		struct group_info *gi = filp->f_cred->group_info;
> +
> +		if (gid_gte(filp->f_cred->fsgid, gid_min) &&
> +		    gid_lte(filp->f_cred->fsgid, gid_max))
> +			match = true;
> +
> +		if (!match && (info->match & XT_SUPPL_GROUPS) && gi) {
> +			for (i = 0; i < gi->ngroups; ++i) {
> +				kgid_t group = gi->gid[i];
> +
> +				if (gid_gte(group, gid_min) &&
> +				    gid_lte(group, gid_max)) {
> +					match = true;
> +					break;
> +				}
> +			}
> +		}
> +
> +		if (match ^ !(info->invert & XT_OWNER_GID))
>  			return false;
>  	}
>  
> 

How can this be safe on SMP ?