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, 19 insertions, 7 deletions

diff --git a/posix/execvpe.c b/posix/execvpe.c
index 859c0f69bf..ea67d19fcd 100644
--- a/posix/execvpe.c
+++ b/posix/execvpe.c
@@ -67,11 +67,9 @@ maybe_script_execute (const char *file, char *const argv[], char *const envp[])
   __execve (new_argv[0], new_argv, envp);
 }
 
-
-/* Execute FILE, searching in the `PATH' environment variable if it contains
-   no slashes, with arguments ARGV and environment from ENVP.  */
-int
-__execvpe (const char *file, char *const argv[], char *const envp[])
+static int
+__execvpe_common (const char *file, char *const argv[], char *const envp[],
+	          bool exec_script)
 {
   /* We check the simple case first. */
   if (*file == '\0')
@@ -85,7 +83,7 @@ __execvpe (const char *file, char *const argv[], char *const envp[])
     {
       __execve (file, argv, envp);
 
-      if (errno == ENOEXEC)
+      if (errno == ENOEXEC && exec_script)
         maybe_script_execute (file, argv, envp);
 
       return -1;
@@ -137,7 +135,7 @@ __execvpe (const char *file, char *const argv[], char *const envp[])
 
       __execve (buffer, argv, envp);
 
-      if (errno == ENOEXEC)
+      if (errno == ENOEXEC && exec_script)
         /* This has O(P*C) behavior, where P is the length of the path and C
            is the argument count.  A better strategy would be allocate the
            substitute argv and reuse it each time through the loop (so it
@@ -184,4 +182,18 @@ __execvpe (const char *file, char *const argv[], char *const envp[])
   return -1;
 }
 
+/* Execute FILE, searching in the `PATH' environment variable if it contains
+   no slashes, with arguments ARGV and environment from ENVP.  */
+int
+__execvpe (const char *file, char *const argv[], char *const envp[])
+{
+  return __execvpe_common (file, argv, envp, true);
+}
 weak_alias (__execvpe, execvpe)
+
+/* Same as __EXECVPE, but does not try to execute NOEXEC files.  */
+int
+__execvpex (const char *file, char *const argv[], char *const envp[])
+{
+  return __execvpe_common (file, argv, envp, false);
+}