From f9f78a2cbfdb91b7505fbd3360183d17dd79d409 Mon Sep 17 00:00:00 2001
From: "Roland C. Dowdeswell" <elric@imrryr.org>
Date: Thu, 31 May 2012 17:30:29 +0100
Subject: [PATCH] kadm5_log_reinit() needs to obtain its lock before truncating
 the file.

We can't use O_TRUNC on open because (without O_EXLOCK which is
not portable) we would be modifying the file without an exclusive
lock.  So, we drop the use of O_TRUNC and use ftruncate(2) after
obtaining the lock via flock(2).
---
 lib/kadm5/log.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/lib/kadm5/log.c b/lib/kadm5/log.c
index 659a9c5e9..5ace4682d 100644
--- a/lib/kadm5/log.c
+++ b/lib/kadm5/log.c
@@ -124,6 +124,7 @@ kadm5_ret_t
 kadm5_log_reinit (kadm5_server_context *context)
 {
     int fd;
+    int ret;
     kadm5_log_context *log_context = &context->log_context;
 
     if (log_context->log_fd != -1) {
@@ -131,12 +132,18 @@ kadm5_log_reinit (kadm5_server_context *context)
 	close (log_context->log_fd);
 	log_context->log_fd = -1;
     }
-    fd = open (log_context->log_file, O_RDWR | O_CREAT | O_TRUNC, 0600);
+    fd = open (log_context->log_file, O_RDWR | O_CREAT, 0600);
     if (fd < 0)
 	return errno;
     if (flock (fd, LOCK_EX) < 0) {
+	ret = errno;
 	close (fd);
-	return errno;
+	return ret;
+    }
+    if (ftruncate(fd, 0) < 0) {
+	ret = errno;
+	close(fd);
+	return ret;
     }
 
     log_context->version = 0;