[PATCH] netfilter: xt_owner: Add complementary groups option

[Lukasz Pawelczyk <l.pawelczyk@xxxxxxxxxxx>]

The XT_COMPL_GROUPS flag causes GIDs specified with XT_OWNER_GID to
be also checked in the complementary 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..67901269873d 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_COMPL_GROUPS = 1 << 3,
 };
 
 struct xt_owner_match_info {
diff --git a/net/netfilter/xt_owner.c b/net/netfilter/xt_owner.c
index 46686fb73784..1c581c14b2ab 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_COMPL_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;
 	}
 
-- 
2.20.1