linux-kernel - [PATCH 3.16 15/61] selinux: properly handle multiple messages in selinux_netlink

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Message-ID: <lsq.1591725832.420858282@decadent.org.uk>
Date:   Tue, 09 Jun 2020 19:04:06 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Dmitry Vyukov" <dvyukov@...gle.com>, stable@...r.kernel.org,
        "Paul Moore" <paul@...l-moore.com>,
        "Stephen Smalley" <stephen.smalley.work@...il.com>
Subject: [PATCH 3.16 15/61] selinux: properly handle multiple messages in
 selinux_netlink_send()

3.16.85-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Paul Moore <paul@...l-moore.com>

commit fb73974172ffaaf57a7c42f35424d9aece1a5af6 upstream.

Fix the SELinux netlink_send hook to properly handle multiple netlink
messages in a single sk_buff; each message is parsed and subject to
SELinux access control.  Prior to this patch, SELinux only inspected
the first message in the sk_buff.

Cc: stable@...r.kernel.org
Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Reviewed-by: Stephen Smalley <stephen.smalley.work@...il.com>
Signed-off-by: Paul Moore <paul@...l-moore.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -4669,39 +4669,59 @@ static int selinux_tun_dev_open(void *se
 
 static int selinux_nlmsg_perm(struct sock *sk, struct sk_buff *skb)
 {
-	int err = 0;
-	u32 perm;
+	int rc = 0;
+	unsigned int msg_len;
+	unsigned int data_len = skb->len;
+	unsigned char *data = skb->data;
 	struct nlmsghdr *nlh;
 	struct sk_security_struct *sksec = sk->sk_security;
+	u16 sclass = sksec->sclass;
+	u32 perm;
 
-	if (skb->len < NLMSG_HDRLEN) {
-		err = -EINVAL;
-		goto out;
-	}
-	nlh = nlmsg_hdr(skb);
+	while (data_len >= nlmsg_total_size(0)) {
+		nlh = (struct nlmsghdr *)data;
 
-	err = selinux_nlmsg_lookup(sksec->sclass, nlh->nlmsg_type, &perm);
-	if (err) {
-		if (err == -EINVAL) {
+		/* NOTE: the nlmsg_len field isn't reliably set by some netlink
+		 *       users which means we can't reject skb's with bogus
+		 *       length fields; our solution is to follow what
+		 *       netlink_rcv_skb() does and simply skip processing at
+		 *       messages with length fields that are clearly junk
+		 */
+		if (nlh->nlmsg_len < NLMSG_HDRLEN || nlh->nlmsg_len > data_len)
+			return 0;
+
+		rc = selinux_nlmsg_lookup(sclass, nlh->nlmsg_type, &perm);
+		if (rc == 0) {
+			rc = sock_has_perm(current, sk, perm);
+			if (rc)
+				return rc;
+		} else if (rc == -EINVAL) {
+			/* -EINVAL is a missing msg/perm mapping */
 			pr_warn_ratelimited("SELinux: unrecognized netlink"
-			       " message: protocol=%hu nlmsg_type=%hu sclass=%s"
-			       " pig=%d comm=%s\n",
-			       sk->sk_protocol, nlh->nlmsg_type,
-			       secclass_map[sksec->sclass - 1].name,
-			       task_pid_nr(current), current->comm);
-			if (!selinux_enforcing || security_get_allow_unknown())
-				err = 0;
+				" message: protocol=%hu nlmsg_type=%hu sclass=%s"
+				" pid=%d comm=%s\n",
+				sk->sk_protocol, nlh->nlmsg_type,
+				secclass_map[sclass - 1].name,
+				task_pid_nr(current), current->comm);
+			if (selinux_enforcing && !security_get_allow_unknown())
+				return rc;
+			rc = 0;
+		} else if (rc == -ENOENT) {
+			/* -ENOENT is a missing socket/class mapping, ignore */
+			rc = 0;
+		} else {
+			return rc;
 		}
 
-		/* Ignore */
-		if (err == -ENOENT)
-			err = 0;
-		goto out;
+		/* move to the next message after applying netlink padding */
+		msg_len = NLMSG_ALIGN(nlh->nlmsg_len);
+		if (msg_len >= data_len)
+			return 0;
+		data_len -= msg_len;
+		data += msg_len;
 	}
 
-	err = sock_has_perm(current, sk, perm);
-out:
-	return err;
+	return rc;
 }
 
 #ifdef CONFIG_NETFILTER