From 20e1db19db5d6b9e4e83021595eab0dc8f107bef Mon Sep 17 00:00:00 2001 From: Pablo Neira Ayuso Date: Thu, 23 Aug 2012 02:09:11 +0000 Subject: 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 Signed-off-by: David S. Miller --- net/netlink/af_netlink.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'net/netlink') diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index 1445d73533e..527023823b5 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -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(); } -- cgit v1.2.3-70-g09d2