If -f is used and the output file name with ".new" appended already

exists, unlink it first and then create it safely rather than
truncating it.  This is much safer when creating files in a
world-writable directory.

Also add documentation for keytab merging.

1 files changed, 4 insertions, 1 deletions

diff --git a/client/file.c b/client/file.c
index ce25ab5..17f0f23 100644
--- a/client/file.c
+++ b/client/file.c
@@ -26,7 +26,10 @@ overwrite_file(const char *name, const void *data, size_t length)
     int fd;
     ssize_t status;
 
-    fd = open(name, O_WRONLY | O_CREAT | O_TRUNC, 0600);
+    if (access(name, F_OK) == 0)
+        if (unlink(name) < 0)
+            sysdie("unable to delete existing file %s", name);
+    fd = open(name, O_WRONLY | O_CREAT | O_EXCL, 0600);
     if (fd < 0)
         sysdie("open of %s failed", name);
     status = write(fd, data, length);