From: Eli Zaretskii <eliz@gnu.org>
Date: Wed, 27 Feb 2013 18:37:31 +0000 (+0200)
Subject: Fix race conditions with MS-Windows lock files by using _sopen.
X-Git-Tag: emacs-24.3.90~173^2~6^2~31
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=531e70eca4c3bcd44942a67f5ea1a8bb1cb41dad;p=emacs.git

Fix race conditions with MS-Windows lock files by using _sopen.

 src/filelock.c (create_lock_file) [WINDOWSNT]: Use _sopen with
 _SH_DENYRW flag, instead of emacs_open, to deny any other process
 access to the lock file until it is written and closed.

Fixes: debbugs:13807
---

diff --git a/src/ChangeLog b/src/ChangeLog
index f5617487fda..4135dadf28a 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,10 @@
+2013-02-27  Eli Zaretskii  <eliz@gnu.org>
+
+	* filelock.c (create_lock_file) [WINDOWSNT]: Use _sopen with
+	_SH_DENYRW flag, instead of emacs_open, to deny any other process
+	access to the lock file until it is written and closed.
+	(Bug#13807)
+
 2013-02-27  Paul Eggert  <eggert@cs.ucla.edu>
 
 	* callint.c (Qcall_interactively):
diff --git a/src/filelock.c b/src/filelock.c
index 4d556de2454..78cd60a12e1 100644
--- a/src/filelock.c
+++ b/src/filelock.c
@@ -44,6 +44,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include "coding.h"
 #include "systime.h"
 #ifdef WINDOWSNT
+#include <share.h>
 #include "w32.h"	/* for dostounix_filename */
 #endif
 
@@ -353,12 +354,17 @@ create_lock_file (char *lfname, char *lock_info_str, bool force)
      create a regular file with the lock info written as its
      contents.  */
   {
-    int fd = emacs_open (lfname, O_WRONLY | O_BINARY | O_CREAT | O_EXCL,
-			 S_IREAD | S_IWRITE);
+    /* Deny everybody else any kind of access to the file until we are
+       done writing it and close the handle.  This makes the entire
+       open/write/close operation atomic, as far as other processes
+       are concerned.  */
+    int fd = _sopen (lfname,
+		     _O_WRONLY | _O_BINARY | _O_CREAT | _O_EXCL | _O_NOINHERIT,
+		     _SH_DENYRW, S_IREAD | S_IWRITE);
 
     if (fd < 0 && errno == EEXIST && force)
-      fd = emacs_open (lfname, O_WRONLY | O_BINARY | O_TRUNC,
-		       S_IREAD | S_IWRITE);
+      fd = _sopen (lfname, _O_WRONLY | _O_BINARY | _O_TRUNC |_O_NOINHERIT,
+		   _SH_DENYRW, S_IREAD | S_IWRITE);
     if (fd >= 0)
       {
 	ssize_t lock_info_len = strlen (lock_info_str);