lib/: set O_CLOEXEC on all fds

As found by
  git grep -E '(open|setmntent|pipe2?)\(' |
    grep -vE '((zfs|zpool)_|fd|dl|lzc_re|pidfile_|g_)open\('

FreeBSD's pidfile_open() says nothing about the flags of the files it
opens, but we can't do anything about it anyway; the implementation does
open all files with O_CLOEXEC

Consider this output with zpool.d/media appended with
"pid=$$; (ls -l /proc/$pid/fd > /dev/tty)":
  $ /sbin/zpool iostat -vc media
  lrwx------ 0 -> /dev/pts/0
  l-wx------ 1 -> 'pipe:[3278500]'
  l-wx------ 2 -> /dev/null
  lrwx------ 3 -> /dev/zfs
  lr-x------ 4 -> /proc/31895/mounts
  lrwx------ 5 -> /dev/zfs
  lr-x------ 10 -> /usr/lib/zfs-linux/zpool.d/media
vs
  $ ./zpool iostat -vc vendor,upath,iostat,media
  lrwx------ 0 -> /dev/pts/0
  l-wx------ 1 -> 'pipe:[3279887]'
  l-wx------ 2 -> /dev/null
  lr-x------ 10 -> /usr/lib/zfs-linux/zpool.d/media

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Ahelenia Ziemiańska <[email protected]>
Closes #11866

1 files changed, 4 insertions, 6 deletions

diff --git a/lib/libzfs/libzfs_pool.c b/lib/libzfs/libzfs_pool.c
index 9ef97cd67..12de6887d 100644
--- a/lib/libzfs/libzfs_pool.c
+++ b/lib/libzfs/libzfs_pool.c
@@ -4809,13 +4809,11 @@ zpool_load_compat(const char *compatibility,
 	 * as they're only needed if the filename is relative
 	 * which will be checked during the openat().
 	 */
-#ifdef O_PATH
-	sdirfd = open(ZPOOL_SYSCONF_COMPAT_D, O_DIRECTORY | O_PATH);
-	ddirfd = open(ZPOOL_DATA_COMPAT_D, O_DIRECTORY | O_PATH);
-#else
-	sdirfd = open(ZPOOL_SYSCONF_COMPAT_D, O_DIRECTORY | O_RDONLY);
-	ddirfd = open(ZPOOL_DATA_COMPAT_D, O_DIRECTORY | O_RDONLY);
+#ifndef O_PATH
+#define	O_PATH O_RDONLY
 #endif
+	sdirfd = open(ZPOOL_SYSCONF_COMPAT_D, O_DIRECTORY | O_PATH | O_CLOEXEC);
+	ddirfd = open(ZPOOL_DATA_COMPAT_D, O_DIRECTORY | O_PATH | O_CLOEXEC);
 
 	(void) strlcpy(filenames, compatibility, ZFS_MAXPROPLEN);
 	file = strtok_r(filenames, ",", &ps);