GNU bug report logs - #61095
possible misuse of posix_spawn API on non-linux OSes

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From: Ludovic Courtès <ludo <at> gnu.org>
To: 61095 <at> debbugs.gnu.org
Cc: Ludovic Courtès <ludo <at> gnu.org>, Josselin Poiret <dev <at> jpoiret.xyz>, Omar Polo <op <at> omarpolo.com>, Andrew Whatson <whatson <at> tailcall.au>
Subject: bug#61095: [PATCH 3/3] Use 'posix_spawn_file_actions_addclosefrom_np' where available.
Date: Thu, 30 Mar 2023 00:30:57 +0200

* configure.ac: Check for 'posix_spawn_file_actions_addclosefrom_np'.
* libguile/posix.c (HAVE_ADDCLOSEFROM): New macro.
(close_inherited_fds): Wrap in #ifdef HAVE_ADDCLOSEFROM.
(do_spawn) [HAVE_ADDCLOSEFROM]: Use 'posix_spawn_file_actions_addclosefrom_np'.
---
 configure.ac     |  4 +++-
 libguile/posix.c | 14 ++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index d5ce1c4ac..4a93be979 100644
--- a/configure.ac
+++ b/configure.ac
@@ -515,6 +515,7 @@ AC_CHECK_HEADERS([crt_externs.h])
 #   sched_getaffinity, sched_setaffinity - GNU extensions (glibc)
 #   sendfile - non-POSIX, found in glibc
 #   pipe2 - non-POSIX, found in glibc (GNU/Linux and GNU/Hurd)
+#   posix_spawn_file_actions_addclosefrom_np - glibc >= 2.34
 #
 AC_CHECK_FUNCS([DINFINITY DQNAN cexp chsize clog clog10 ctermid         \
   fesetround ftime ftruncate fchown fchownat fchmod fchdir readlinkat	\
@@ -528,7 +529,8 @@ AC_CHECK_FUNCS([DINFINITY DQNAN cexp chsize clog clog10 ctermid         \
   index bcopy rindex truncate isblank _NSGetEnviron              \
   strcoll_l strtod_l strtol_l newlocale uselocale utimensat     \
   fstatat futimens openat						\
-  sched_getaffinity sched_setaffinity sendfile pipe2])
+  sched_getaffinity sched_setaffinity sendfile pipe2
+  posix_spawn_file_actions_addclosefrom_np])
 
 # The newlib C library uses _NL_ prefixed locale langinfo constants.
 AC_CHECK_DECLS([_NL_NUMERIC_GROUPING], [], [], [[#include <langinfo.h>]])
diff --git a/libguile/posix.c b/libguile/posix.c
index b5830c43b..3adc743c4 100644
--- a/libguile/posix.c
+++ b/libguile/posix.c
@@ -1322,6 +1322,12 @@ SCM_DEFINE (scm_fork, "primitive-fork", 0, 0, 0,
 #undef FUNC_NAME
 #endif /* HAVE_FORK */
 
+#ifdef HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCLOSEFROM_NP
+# define HAVE_ADDCLOSEFROM 1
+#endif
+
+#ifndef HAVE_ADDCLOSEFROM
+
 static void
 close_inherited_fds (posix_spawn_file_actions_t *actions, int max_fd)
 {
@@ -1346,6 +1352,8 @@ close_inherited_fds (posix_spawn_file_actions_t *actions, int max_fd)
     }
 }
 
+#endif
+
 static pid_t
 do_spawn (char *exec_file, char **exec_argv, char **exec_env,
           int in, int out, int err, int spawnp)
@@ -1389,7 +1397,13 @@ do_spawn (char *exec_file, char **exec_argv, char **exec_env,
   posix_spawn_file_actions_adddup2 (&actions, fd_slot[1], 1);
   posix_spawn_file_actions_adddup2 (&actions, fd_slot[2], 2);
 
+#ifdef HAVE_ADDCLOSEFROM
+  /* This function appears in glibc 2.34.  It's both free from race
+     conditions and more efficient than the alternative.  */
+  posix_spawn_file_actions_addclosefrom_np (&actions, 3);
+#else
   close_inherited_fds (&actions, max_fd);
+#endif
 
   int res = -1;
   if (spawnp)
-- 
2.39.2

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