From d53beee9e511af84fb39cd2aa6c1c1cc3cfd06d2 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Sun, 4 Feb 2007 15:01:41 +0000
Subject: Use SCM_CREDENTIALS for authentication of netlink data from kernel

git-svn-id: file:///home/lennart/svn/public/avahi/trunk@1381 941a03a8-eaeb-0310-b9a0-b1bbd8fe43fe
---
 avahi-autoipd/iface-linux.c | 38 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/avahi-autoipd/iface-linux.c b/avahi-autoipd/iface-linux.c
index 2ad8a61..55e1da6 100644
--- a/avahi-autoipd/iface-linux.c
+++ b/avahi-autoipd/iface-linux.c
@@ -66,6 +66,7 @@ AVAHI_LLIST_HEAD(Address, addresses) = NULL;
 
 int iface_init(int i) {
     struct sockaddr_nl addr;
+    int on = 1;
     
     if ((fd = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE)) < 0) {
         daemon_log(LOG_ERR, "socket(PF_NETLINK): %s", strerror(errno));
@@ -81,6 +82,11 @@ int iface_init(int i) {
         daemon_log(LOG_ERR, "bind(): %s", strerror(errno));
         goto fail;
     }
+    
+    if (setsockopt(fd, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on)) < 0) {
+        daemon_log(LOG_ERR, "SO_PASSCRED: %s", strerror(errno));
+        goto fail;
+    }
 
     ifindex = i;
     
@@ -179,13 +185,41 @@ static int process_response(int wait_for_done, unsigned seq) {
         size_t bytes;
         ssize_t r;
         char replybuf[2048];
+        char cred_msg[CMSG_SPACE(sizeof(struct ucred))];
+        struct msghdr msghdr;
+        struct cmsghdr *cmsghdr;
+        struct ucred *ucred;
+        struct iovec iov; 
         struct nlmsghdr *p = (struct nlmsghdr *) replybuf;
+        
+        memset(&iov, 0, sizeof(iov));
+        iov.iov_base = replybuf; 
+ 	iov.iov_len = sizeof(replybuf);
+
+        memset(&msghdr, 0, sizeof(msghdr));
+        msghdr.msg_name = (void*) NULL;
+        msghdr.msg_namelen = 0; 
+        msghdr.msg_iov = &iov; 
+        msghdr.msg_iovlen = 1; 
+        msghdr.msg_control = cred_msg; 
+        msghdr.msg_controllen = sizeof(cred_msg); 
+ 	msghdr.msg_flags = 0;
+        
+        if ((r = recvmsg(fd, &msghdr, 0)) < 0) {
+            daemon_log(LOG_ERR, "recvmsg() failed: %s", strerror(errno));
+            return -1;
+        }
 
-        if ((r = recv(fd, replybuf, sizeof(replybuf), 0)) < 0) {
-            daemon_log(LOG_ERR, "recv() failed: %s", strerror(errno));
+        if (!(cmsghdr = CMSG_FIRSTHDR(&msghdr)) || cmsghdr->cmsg_type != SCM_CREDENTIALS) {
+            daemon_log(LOG_WARNING, "No sender credentials received, ignoring data."); 
             return -1;
         }
 
+        ucred = (struct ucred*) CMSG_DATA(cmsghdr);
+        
+        if (ucred->uid != 0)
+            return -1;
+
         bytes = (size_t) r;
         
         for (; bytes > 0; p = NLMSG_NEXT(p, bytes)) {
-- 
cgit