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

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Message #22 received at 61095 <at> debbugs.gnu.org (full text, mbox):

From: Ludovic Courtès <ludo <at> gnu.org>
To: 61095 <at> debbugs.gnu.org
Cc: Ludovic Courtès <ludo <at> gnu.org>
Subject: [PATCH 1/3] 'spawn' closes only open file descriptors on
 non-GNU/Linux systems.
Date: Thu, 30 Mar 2023 00:30:55 +0200

Fixes <https://bugs.gnu.org/61095>.
Reported by Omar Polo <op <at> omarpolo.com>.

* libguile/posix.c (close_inherited_fds_slow): On systems other than
GNU/Linux, call 'addclose' only when 'fcntl' succeeds on MAX_FD.
---
 libguile/posix.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/libguile/posix.c b/libguile/posix.c
index 3a8be94e4..68e9bfade 100644
--- a/libguile/posix.c
+++ b/libguile/posix.c
@@ -1326,7 +1326,24 @@ static void
 close_inherited_fds_slow (posix_spawn_file_actions_t *actions, int max_fd)
 {
   while (--max_fd > 2)
-    posix_spawn_file_actions_addclose (actions, max_fd);
+    {
+      /* Adding a 'close' action for a file descriptor that is not open
+         causes 'posix_spawn' to fail on GNU/Hurd and on OpenBSD, but
+         not on GNU/Linux: <https://bugs.gnu.org/61095>.  Hence this
+         strategy:
+
+           - On GNU/Linux, close every FD, since that's the only
+             race-free way to make sure the child doesn't inherit one.
+           - On other systems, only close FDs currently open in the
+             parent; it works, but it's racy (XXX).
+
+         The only reliable option is 'addclosefrom'.  */
+#if ! (defined __GLIBC__ && defined __linux__)
+      int flags = fcntl (max_fd, F_GETFD, NULL);
+      if (flags >= 0)
+#endif
+        posix_spawn_file_actions_addclose (actions, max_fd);
+    }
 }
 
 static void

base-commit: e334e59589c3cbfc68d3f7d0d739000e0876b36d
-- 
2.39.2

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