[RFC][PATCH]: match supplementary gids in owner match

[Patrick McHardy <kaber@trash.net>]

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This patch adds support for matching supplementary gids to the owner match.
I wrote it for someone else, i haven't even tested it. According to him, 
it works as
expected. If someone likes it, feel free to add to pom. I was thinking 
about making
an extra flag so normal behaviour would be as before and matching 
supplementary
gid matching would be optional. If someone wants this, just tell me.

Bye
Patrick

[-- Attachment #2: ipt_owner-supgids.diff --]
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===== net/ipv4/netfilter/ipt_owner.c 1.3 vs edited =====
--- 1.3/net/ipv4/netfilter/ipt_owner.c	Thu Aug  8 16:55:29 2002
+++ edited/net/ipv4/netfilter/ipt_owner.c	Mon Jul 14 19:25:36 2003
@@ -109,6 +109,49 @@
 }
 
 static int
+match_gid(const struct sk_buff *skb, gid_t gid)
+{
+	struct task_struct *p;
+	struct files_struct *files;
+	int i;
+
+	/* direct match */
+	if (gid == skb->sk->socket->file->f_gid)
+		return 1;
+
+	/* find owner of socket and check supplementary gids */
+	read_lock(&tasklist_lock);
+	for_each_task(p) {
+		/* racy, owner could have called setfsgid */
+		if (p->fsgid != skb->sk->socket->file->f_gid)
+			continue;
+
+		task_lock(p);
+		files = p->files;
+		if(files) {
+			read_lock(&files->file_lock);
+			for (i=0; i < files->max_fds; i++) {
+				if (fcheck_files(files, i) == skb->sk->socket->file) {
+					int j, ret = 0;
+					read_unlock(&files->file_lock);
+					for (j = 0; j < p->ngroups; j++)
+						if (p->groups[j] == gid) {
+							ret = 1;
+							break;
+						}
+					task_unlock(p);
+					read_unlock(&tasklist_lock);
+					return ret;
+				}
+			}
+			read_unlock(&files->file_lock);
+		}
+		task_unlock(p);
+	}
+	read_unlock(&tasklist_lock);
+	return 0;
+}
+static int
 match(const struct sk_buff *skb,
       const struct net_device *in,
       const struct net_device *out,
@@ -130,7 +173,7 @@
 	}
 
 	if(info->match & IPT_OWNER_GID) {
-		if((skb->sk->socket->file->f_gid != info->gid) ^
+		if(!match_gid(skb, info->gid) ^
 		    !!(info->invert & IPT_OWNER_GID))
 			return 0;
 	}