[PATCH] Do not listen if rtnl_send() fails in ip link iplink_have_newlink() test

["Petr Písař" <ppisar@redhat.com>]

If rtnl_send() fails in iplink_have_newlink() test, listening for
response will result in indefinite hang. This can be demonstrated by
"ip link show" while SELinux preventing from sending the RTM_NEWLINK
over netlink.

This patch checks for the return value as is done at all other
rtnl_send() calls. It falls back to IOCTL in case of failure.

Signed-off-by: Petr Písař <ppisar@redhat.com>
---
 ip/iplink.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/ip/iplink.c b/ip/iplink.c
index 58b6c20..5132868 100644
--- a/ip/iplink.c
+++ b/ip/iplink.c
@@ -178,8 +178,13 @@ static int iplink_have_newlink(void)
 		req.n.nlmsg_type = RTM_NEWLINK;
 		req.i.ifi_family = AF_UNSPEC;
 
-		rtnl_send(&rth, &req.n, req.n.nlmsg_len);
-		rtnl_listen(&rth, accept_msg, NULL);
+		if (rtnl_send(&rth, &req.n, req.n.nlmsg_len) < 0) {
+			perror("Could not check for "
+				"link configuration over netlink support");
+			have_rtnl_newlink = 0;
+		} else {
+			rtnl_listen(&rth, accept_msg, NULL);
+		}
 	}
 	return have_rtnl_newlink;
 }
-- 
1.8.3.1