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

[Tomas Hozza <thozza@redhat.com>]

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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.


Regards,

Tomas Hozza
Associate Software Engineer
BaseOS - Brno, CZ

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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