Re: Two netlink patches

[Serge Hallyn <serue us ibm com>]

Well, the attached (compiled, but untested) patch does move the code
into audit.c the way Chris wanted, adding only one line to
dummy_netlink_send and cap_netlink_send.  But it also would require some
changes to SELinux, I assume, to at least handle the new CAP_AUDIT bit.

By extending the NETLINK_CREDS(skb), I assume you mean adding a void
*security?  Perhaps that's actually the cleaner way to go, if only
because it lets the actual receiving subsystem perform the check, rather
than netlink.  That's the part I don't like about my patch.  While in
this case it's just audit, that may change, and soon
security_netlink_send becomes a central location for checks for all
sorts of protocols...

So does extending NETLINK_CREDS seem (politically) feasible?  Or does
the attached patch seem acceptable?

-serge

On Thu, 2004-12-16 at 10:29 -0500, Stephen Smalley wrote:
> On Thu, 2004-12-16 at 11:25, Serge Hallyn wrote:
> > Hi,
> > 
> > I believe a single CAP_AUDIT_CONTROL bit should suffice for defining an
> > MRMLOSPP-compliant audit role.  I will send out a new patch asap which
> > also nixes cap_netlink_audit_send and just leaves the code in dummy.
> > 
> > Does this seem sufficient?  Or do you (Chris) object to having this test
> > in the netlink send codepath?  As far as I can see, the only legitimate
> > alternative would be to in fact move audit control to a different
> > (pseudo-fs?) interface.
> 
> For just a capability check, you can check on the receive path based on
> NETLINK_CREDS(skb)->eff_cap, as long as the security modules set all of
> the capability bits in that field properly (commoncap already does so,
> and SELinux and dummy could easily be changed to do so).  In contrast,
> we don't have that option for SELinux permissions, because we don't have
> any way to convey either the sender security context or the computed
> permissions in NETLINK_CREDS without extending that structure. 
> 
-- 
Serge Hallyn <serue us ibm com>

Index: linux-2.6.9/include/linux/audit.h
===================================================================
--- linux-2.6.9.orig/include/linux/audit.h	2004-12-15 17:42:23.000000000 -0600
+++ linux-2.6.9/include/linux/audit.h	2004-12-16 10:44:24.000000000 -0600
@@ -193,6 +193,8 @@ extern void		    audit_send_reply(int pi
 					     int done, int multi,
 					     void *payload, int size);
 extern void		    audit_log_lost(const char *message);
+struct sk_buff;
+extern int		    audit_netlink_ok(struct sk_buff *skb);
 #else
 #define audit_log(t,f,...) do { ; } while (0)
 #define audit_log_start(t) ({ NULL; })
@@ -206,6 +208,7 @@ extern void		    audit_log_lost(const ch
 #define audit_set_backlog_limit(l) do { ; } while (0)
 #define audit_set_enabled(s) do { ; } while (0)
 #define audit_set_failure(s) do { ; } while (0)
+#define audit_netlink_ok(n) do { 0; } while (0)
 #endif
 #endif
 #endif
Index: linux-2.6.9/include/linux/capability.h
===================================================================
--- linux-2.6.9.orig/include/linux/capability.h	2004-12-16 10:27:20.000000000 -0600
+++ linux-2.6.9/include/linux/capability.h	2004-12-16 10:27:32.000000000 -0600
@@ -284,6 +284,10 @@ typedef __u32 kernel_cap_t;
 
 #define CAP_LEASE            28
 
+/* Allow control of audit subsystem */
+
+#define CAP_AUDIT	     29
+
 #ifdef __KERNEL__
 /* 
  * Bounding set
Index: linux-2.6.9/include/linux/netlink.h
===================================================================
--- linux-2.6.9.orig/include/linux/netlink.h	2004-12-02 16:08:23.000000000 -0600
+++ linux-2.6.9/include/linux/netlink.h	2004-12-02 16:14:17.000000000 -0600
@@ -120,6 +120,7 @@ extern int netlink_attach(int unit, int 
 extern void netlink_detach(int unit);
 extern int netlink_post(int unit, struct sk_buff *skb);
 extern struct sock *netlink_kernel_create(int unit, void (*input)(struct sock *sk, int len));
+extern int netlink_get_msgtype(struct sk_buff *skb);
 extern void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err);
 extern int netlink_unicast(struct sock *ssk, struct sk_buff *skb, __u32 pid, int nonblock);
 extern int netlink_broadcast(struct sock *ssk, struct sk_buff *skb, __u32 pid,
Index: linux-2.6.9/kernel/audit.c
===================================================================
--- linux-2.6.9.orig/kernel/audit.c	2004-12-02 16:02:22.000000000 -0600
+++ linux-2.6.9/kernel/audit.c	2004-12-16 10:46:25.000000000 -0600
@@ -327,8 +327,8 @@ static int audit_receive_msg(struct sk_b
 				 &status_set, sizeof(status_set));
 		break;
 	case AUDIT_SET:
-		if (!capable(CAP_SYS_ADMIN))
-			return -EPERM;
+		if (nlh->nlmsg_len < sizeof(struct audit_status))
+			return -EINVAL;
 		status_get   = (struct audit_status *)data;
 		if (status_get->mask & AUDIT_STATUS_ENABLED) {
 			err = audit_set_enabled(status_get->enabled);
@@ -364,8 +364,8 @@ static int audit_receive_msg(struct sk_b
 		audit_log_end(ab);
 		break;
 	case AUDIT_LOGIN:
-		if (!capable(CAP_SYS_ADMIN))
-			return -EPERM;
+		if (nlh->nlmsg_len < sizeof(struct audit_login))
+			return -EINVAL;
 		login = (struct audit_login *)data;
 		ab = audit_log_start(NULL);
 		if (ab) {
@@ -384,9 +384,12 @@ static int audit_receive_msg(struct sk_b
 					 login->loginuid);
 #endif
 		break;
-	case AUDIT_LIST:
 	case AUDIT_ADD:
 	case AUDIT_DEL:
+		if (nlh->nlmsg_len < sizeof(struct audit_rule))
+			return -EINVAL;
+		/* fallthrough */
+	case AUDIT_LIST:
 #ifdef CONFIG_AUDITSYSCALL
 		err = audit_receive_filter(nlh->nlmsg_type, pid, uid, seq,
 					   data);
@@ -810,3 +813,38 @@ void audit_log(struct audit_context *ctx
 		audit_log_end(ab);
 	}
 }
+
+int audit_netlink_ok(struct sk_buff *skb)
+{
+	int err = 0;
+	int msgtype;
+	
+	if (!skb || !skb->sk || skb->sk->sk_protocol != NETLINK_AUDIT)
+		goto out;
+
+	msgtype = netlink_get_msgtype(skb);
+
+	switch(msgtype) {
+		case 0:  /* not an audit msg */
+
+		case AUDIT_GET:
+		case AUDIT_LIST:
+			break;
+
+		case AUDIT_SET:
+		case AUDIT_USER:
+		case AUDIT_LOGIN:
+
+		case AUDIT_ADD:
+		case AUDIT_DEL:
+			if (!capable(CAP_AUDIT))
+				err = -EPERM;
+			break;
+
+		default:  /* permission denied: bad msg */
+			err = -EINVAL;
+	}
+
+out:
+	return err;
+}
Index: linux-2.6.9/kernel/auditsc.c
===================================================================
--- linux-2.6.9.orig/kernel/auditsc.c	2004-12-02 16:02:22.000000000 -0600
+++ linux-2.6.9/kernel/auditsc.c	2004-12-15 15:27:16.000000000 -0600
@@ -250,8 +250,6 @@ int audit_receive_filter(int type, int p
 		audit_send_reply(pid, seq, AUDIT_LIST, 1, 1, NULL, 0);
 		break;
 	case AUDIT_ADD:
-		if (!capable(CAP_SYS_ADMIN))
-			return -EPERM;
 		if (!(entry = kmalloc(sizeof(*entry), GFP_KERNEL)))
 			return -ENOMEM;
 		if (audit_copy_rule(&entry->rule, data)) {
Index: linux-2.6.9/net/netlink/af_netlink.c
===================================================================
--- linux-2.6.9.orig/net/netlink/af_netlink.c	2004-12-02 16:09:27.000000000 -0600
+++ linux-2.6.9/net/netlink/af_netlink.c	2004-12-03 08:52:19.000000000 -0600
@@ -518,6 +518,18 @@ static int netlink_connect(struct socket
 	return err;
 }
 
+int netlink_get_msgtype(struct sk_buff *skb)
+{
+	struct nlmsghdr *nlh = (struct nlmsghdr *)skb->data;
+
+	if (skb->len < NLMSG_SPACE(0))
+		return -EINVAL;
+
+	if (nlh->nlmsg_len < sizeof(*nlh) || skb->len < nlh->nlmsg_len)
+		return -EINVAL;
+	return nlh->nlmsg_type;
+}
+
 static int netlink_getname(struct socket *sock, struct sockaddr *addr, int *addr_len, int peer)
 {
 	struct sock *sk = sock->sk;
@@ -1511,6 +1523,7 @@ MODULE_LICENSE("GPL");
 
 MODULE_ALIAS_NETPROTO(PF_NETLINK);
 
+EXPORT_SYMBOL(netlink_get_msgtype);
 EXPORT_SYMBOL(netlink_ack);
 EXPORT_SYMBOL(netlink_broadcast);
 EXPORT_SYMBOL(netlink_dump_start);
Index: linux-2.6.9/security/commoncap.c
===================================================================
--- linux-2.6.9.orig/security/commoncap.c	2004-12-02 16:08:24.000000000 -0600
+++ linux-2.6.9/security/commoncap.c	2004-12-16 10:39:45.000000000 -0600
@@ -23,11 +23,13 @@
 #include <linux/ptrace.h>
 #include <linux/xattr.h>
 #include <linux/hugetlb.h>
+#include <net/sock.h>
+#include <linux/audit.h>
 
 int cap_netlink_send(struct sock *sk, struct sk_buff *skb)
 {
 	NETLINK_CB(skb).eff_cap = current->cap_effective;
-	return 0;
+	return audit_netlink_ok(skb);
 }
 
 EXPORT_SYMBOL(cap_netlink_send);
Index: linux-2.6.9/security/dummy.c
===================================================================
--- linux-2.6.9.orig/security/dummy.c	2004-12-02 16:08:24.000000000 -0600
+++ linux-2.6.9/security/dummy.c	2004-12-16 10:40:57.000000000 -0600
@@ -732,7 +732,7 @@ static int dummy_netlink_send (struct so
 		cap_raise (NETLINK_CB (skb).eff_cap, CAP_NET_ADMIN);
 	else
 		NETLINK_CB (skb).eff_cap = 0;
-	return 0;
+	return audit_netlink_ok(skb);
 }
 
 static int dummy_netlink_recv (struct sk_buff *skb)