Re: [PATCH] tools/hv/hv_kvp_daemon.c: Netlink source address validation allows DoS

[Tomas Hozza <thozza@redhat.com>]

>From 6199072f8131056efce208f04e6985d1f9968d8e Mon Sep 17 00:00:00 2001
From: Tomas Hozza <thozza@redhat.com>
Date: Mon, 5 Nov 2012 10:08:16 +0100
Subject: [PATCH] Netlink source address validation allows DoS

The source code without this patch caused hypervkvpd to exit when it processed
a spoofed Netlink packet which has been sent from an untrusted local user.
Netlink messages with a non-zero nl_pid source address should just be ignored.
---
 tools/hv/hv_kvp_daemon.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/hv/hv_kvp_daemon.c b/tools/hv/hv_kvp_daemon.c
index 3ea3af2..7d74497 100755
--- a/tools/hv/hv_kvp_daemon.c
+++ b/tools/hv/hv_kvp_daemon.c
@@ -1478,13 +1478,19 @@ int main(void)
 		len = recvfrom(fd, kvp_recv_buffer, sizeof(kvp_recv_buffer), 0,
 				addr_p, &addr_l);
 
-		if (len < 0 || addr.nl_pid) {
+		if (len < 0) {
 			syslog(LOG_ERR, "recvfrom failed; pid:%u error:%d %s",
 					addr.nl_pid, errno, strerror(errno));
 			close(fd);
 			return -1;
 		}
 
+		if (addr.nl_pid) {
+			syslog(LOG_WARNING, "Received packet from untrusted pid:%u",
+					addr.nl_pid);
+			continue;
+		}
+
 		incoming_msg = (struct nlmsghdr *)kvp_recv_buffer;
 		incoming_cn_msg = (struct cn_msg *)NLMSG_DATA(incoming_msg);
 		hv_msg = (struct hv_kvp_msg *)incoming_cn_msg->data;
-- 
1.7.11.7

----- Original Message -----
> 
> 
> > -----Original Message-----
> > From: Tomas Hozza [mailto:thozza@redhat.com]
> > Sent: Tuesday, November 06, 2012 10:21 AM
> > To: gregkh@linuxfoundation.org; linux-kernel@vger.kernel.org;
> > devel@linuxdriverproject.org; apw@canonical.com;
> > jasowang@redhat.com
> > Cc: Olaf Hering; KY Srinivasan
> > Subject: [PATCH] tools/hv/hv_kvp_daemon.c: Netlink source address
> > validation
> > allows DoS
> > 
> > Hi.
> > 
> > After discussion with KY Srinivasan and Olaf Hering I'm sending you
> > a patch for the HyperV KVP daemon distributed in linux kernel
> > "tools/hv/hv_kvp_daemon.c".
> > 
> > There is an issue in the current daemon source causing hyperv kvp
> > daemon
> > to exit when it processes a spoofed Netlink packet which has been
> > sent
> > from an untrusted local user.
> > 
> > This patch is fixing this, so now the Netlink messages with a
> > non-zero
> > nl_pid source address are just ignored.
> 
> You don't want to send the patch as an attachment.  Please send the
> patch
> as part of the mail.
> 
> Regards,
> 
> K. Y
> > 
> > 
> > Regards,
> > 
> > Tomas Hozza
> > Associate Software Engineer
> > BaseOS - Brno, CZ
>