CVE-2012-6689 (published 2016-05-02T10:59Z)

The netlink_sendmsg function in net/netlink/af_netlink.c in the Linux kernel before 3.5.5 does not validate the dst_pid field, which allows local users to have an unspecified impact by spoofing Netlink messages.

Severity: HIGH
CVSS v2 base score: 7.2 (AV:L/AC:L/Au:N/C:C/I:C/A:C)
CVSS v3 base score: 7.8, HIGH (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)

Weakness information:
cwe_id: CWE-284
cwe_name: Improper Access Control
description: The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.
extended_description: 
            Access control involves the use of several protection mechanisms such as:
            
               Authentication (proving the identity of an actor)
               Authorization (ensuring that a given actor can access a resource), and
               Accountability (tracking of activities that were performed)
            
            When any mechanism is not applied or otherwise fails, attackers can compromise the security of the product by gaining privileges, reading sensitive information, executing commands, evading detection, etc.
            There are two distinct behaviors that can introduce access control weaknesses:
               
                  Specification: incorrect privileges, permissions, ownership, etc. are explicitly specified for either the user or the resource (for example, setting a password file to be world-writable, or giving administrator capabilities to a guest user). This action could be performed by the program or the administrator.
                  Enforcement: the mechanism contains errors that prevent it from properly enforcing the specified access control requirements (e.g., allowing the user to specify their own privileges, or allowing a syntactically-incorrect ACL to produce insecure settings). This problem occurs within the program itself, in that it does not actually enforce the intended security policy that the administrator specifies.
               
         
		 

Fix information:
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Pablo Neira Ayuso
author_date: 2012-08-23 02:09:11+00:00
msg: netlink: fix possible spoofing from non-root processes

Non-root user-space processes can send Netlink messages to other
processes that are well-known for being subscribed to Netlink
asynchronous notifications. This allows ilegitimate non-root
process to send forged messages to Netlink subscribers.

The userspace process usually verifies the legitimate origin in
two ways:

a) Socket credentials. If UID != 0, then the message comes from
   some ilegitimate process and the message needs to be dropped.

b) Netlink portID. In general, portID == 0 means that the origin
   of the messages comes from the kernel. Thus, discarding any
   message not coming from the kernel.

However, ctnetlink sets the portID in event messages that has
been triggered by some user-space process, eg. conntrack utility.
So other processes subscribed to ctnetlink events, eg. conntrackd,
know that the event was triggered by some user-space action.

Neither of the two ways to discard ilegitimate messages coming
from non-root processes can help for ctnetlink.

This patch adds capability validation in case that dst_pid is set
in netlink_sendmsg(). This approach is aggressive since existing
applications using any Netlink bus to deliver messages between
two user-space processes will break. Note that the exception is
NETLINK_USERSOCK, since it is reserved for netlink-to-netlink
userspace communication.

Still, if anyone wants that his Netlink bus allows netlink-to-netlink
userspace, then they can set NL_NONROOT_SEND. However, by default,
I don't think it makes sense to allow to use NETLINK_ROUTE to
communicate two processes that are sending no matter what information
that is not related to link/neighbouring/routing. They should be using
NETLINK_USERSOCK instead for that.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: af_netlink.c
change_type: ModificationType.MODIFY
diff: @@ -1373,7 +1373,8 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock,
 		dst_pid = addr->nl_pid;
 		dst_group = ffs(addr->nl_groups);
 		err =  -EPERM;
-		if (dst_group && !netlink_capable(sock, NL_NONROOT_SEND))
+		if ((dst_group || dst_pid) &&
+		    !netlink_capable(sock, NL_NONROOT_SEND))
 			goto out;
 	} else {
 		dst_pid = nlk->dst_pid;
@@ -2147,6 +2148,7 @@ static void __init netlink_add_usersock_entry(void)
 	rcu_assign_pointer(nl_table[NETLINK_USERSOCK].listeners, listeners);
 	nl_table[NETLINK_USERSOCK].module = THIS_MODULE;
 	nl_table[NETLINK_USERSOCK].registered = 1;
+	nl_table[NETLINK_USERSOCK].nl_nonroot = NL_NONROOT_SEND;
 
 	netlink_table_ungrab();
 }

programming_language: C