* keyboard.c (Fopen_dribble_file): Avoid some races.

Fixes: debbugs:17187

2 files changed, 7 insertions, 9 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index cb17738d139..2d7307412b2 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,7 @@
+2014-04-12  Paul Eggert  <eggert@cs.ucla.edu>
+
+        * keyboard.c (Fopen_dribble_file): Avoid some races.  (Bug#17187)
+
 2014-04-12  Eli Zaretskii  <eliz@gnu.org>
 
         * xdisp.c (move_it_by_lines): If a large portion of buffer text is
diff --git a/src/keyboard.c b/src/keyboard.c
index f74ba0ee581..a66054f153f 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -10088,15 +10088,9 @@ This may include sensitive information such as passwords.  */)
     {
       int fd;
       file = Fexpand_file_name (file, Qnil);
-      /* This isn't robust, since eg file could be created after we
-         check whether it exists but before emacs_open.
-         Feel free to improve it, but this is not critical.  (Bug#17187)  */
-      if (! NILP (Ffile_exists_p (file)))
-        {
-          if (chmod (SSDATA (file), 0600) < 0)
-            report_file_error ("Doing chmod", file);
-        }
-      fd = emacs_open (SSDATA (file), O_WRONLY | O_CREAT | O_TRUNC, 0600);
+      fd = emacs_open (SSDATA (file), O_WRONLY | O_CREAT | O_EXCL, 0600);
+      if (fd < 0 && errno == EEXIST && unlink (SSDATA (file)) == 0)
+        fd = emacs_open (SSDATA (file), O_WRONLY | O_CREAT | O_EXCL, 0600);
       dribble = fd < 0 ? 0 : fdopen (fd, "w");
       if (dribble == 0)
         report_file_error ("Opening dribble", file);