posix: Fix posix_spawnp to not execute invalid binaries in non compat mode (BZ#23264)

Current posix_spawnp implementation wrongly tries to execute invalid
binaries (for instance script without shebang) as a shell script in
non compat mode.  It was a regression introduced by
9ff72da471a509a8c19791efe469f47fa6977410 when __spawni started to use
__execvpe instead of __execve (glibc __execvpe try to execute ENOEXEC
as shell script regardless).

This patch fixes it by using an internal symbol (__execvpex) with the
faulty semantic (since compat mode is handled by spawni.c itself).

It was reported by Daniel Drake on libc-help [1].

Checked on x86_64-linux-gnu and i686-linux-gnu.

	[BZ #23264]
	* include/unistd.h (__execvpex): New prototype.
	* posix/Makefile (tests): Add tst-spawn4.
	(tests-internal): Add tst-spawn4-compat.
	* posix/execvpe.c (__execvpe_common, __execvpex): New functions.
	* posix/tst-spawn4-compat.c: New file.
	* posix/tst-spawn4.c: Likewise.
	* sysdeps/unix/sysv/linux/spawni.c (__spawni): Do not interpret invalid
	binaries as shell scripts.
	* sysdeps/posix/spawni.c (__spawni): Likewise.

[1] https://sourceware.org/ml/libc-help/2018-06/msg00012.html

1 files changed, 56 insertions, 0 deletions

diff --git a/posix/tst-spawn4.c b/posix/tst-spawn4.c
new file mode 100644
index 0000000000..e4a1fa3f00
--- /dev/null
+++ b/posix/tst-spawn4.c
@@ -0,0 +1,56 @@
+/* Check if posix_spawn does handle correctly ENOEXEC files.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <spawn.h>
+#include <errno.h>
+#include <unistd.h>
+#include <sys/stat.h>
+
+#include <support/xunistd.h>
+#include <support/check.h>
+#include <support/temp_file.h>
+
+static int
+do_test (void)
+{
+  char *scriptname;
+  int fd = create_temp_file ("tst-spawn4.", &scriptname);
+  TEST_VERIFY_EXIT (fd >= 0);
+
+  const char script[] = "echo it should not happen";
+  xwrite (fd, script, sizeof (script) - 1);
+  xclose (fd);
+
+  TEST_VERIFY_EXIT (chmod (scriptname, 0x775) == 0);
+
+  pid_t pid;
+  int status;
+
+  /* Check if scripts without shebang are correctly not executed.  */
+  status = posix_spawn (&pid, scriptname, NULL, NULL, (char *[]) { 0 },
+                        (char *[]) { 0 });
+  TEST_VERIFY_EXIT (status == ENOEXEC);
+
+  status = posix_spawnp (&pid, scriptname, NULL, NULL, (char *[]) { 0 },
+                         (char *[]) { 0 });
+  TEST_VERIFY_EXIT (status == ENOEXEC);
+
+  return 0;
+}
+
+#include <support/test-driver.c>