posix: Use posix_spawn for wordexp

This patch replaces the fork+exec by posix_spawn on wordexp, which
allows a better scability on Linux and simplifies the thread
cancellation handling.

The only change which can not be implemented with posix_spawn the
/dev/null check to certify it is indeed the expected device.  I am
not sure how effetive this check is since /dev/null tampering means
something very wrong with the system and this is the least of the
issues.  My view is the tests is really out of the place and the
hardening provided is minimum.

If the idea is still to provide such check, I think a possibilty
would be to open /dev/null, check it, add a dup2 file action, and
close the file descriptor.

Checked on powerpc64le-linux-gnu and x86_64-linux-gnu.

	* include/spawn.h (__posix_spawn_file_actions_addopen): New
	prototype.
	* posix/spawn_faction_addopen.c (posix_spawn_file_actions_addopen):
	Add internal alias.
	* posix/wordexp.c (create_environment, free_environment): New
	functions.
	(exec_comm_child, exec_comm): Use posix_spawn instead of fork+exec.
	* posix/wordexp-test.c: Use libsupport.

5 files changed, 126 insertions, 158 deletions

diff --git a/ChangeLog b/ChangeLog
index 1d4f418e17..2e34b2da34 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,14 @@
 2019-10-09  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
 
+	* include/spawn.h (__posix_spawn_file_actions_addopen): New
+	prototype.
+	* posix/spawn_faction_addopen.c (posix_spawn_file_actions_addopen):
+	Add internal alias.
+	* posix/wordexp.c (create_environment, free_environment): New
+	functions.
+	(exec_comm_child, exec_comm): Use posix_spawn instead of fork+exec.
+	* posix/wordexp-test.c: Use libsupport.
+
 	* sysdeps/unix/sysv/linux/mips/mips64/getdents64.c (__getdents64):
 	Add small optimization for older kernel to avoid issuing
 	__NR_getdents64 on each call and replace scratch_buffer usage with
diff --git a/include/spawn.h b/include/spawn.h
index 7fdd965bd7..4a0b1849da 100644
--- a/include/spawn.h
+++ b/include/spawn.h
@@ -11,6 +11,9 @@ __typeof (posix_spawn_file_actions_addclose)
 __typeof (posix_spawn_file_actions_adddup2)
   __posix_spawn_file_actions_adddup2 attribute_hidden;
 
+__typeof (posix_spawn_file_actions_addopen)
+  __posix_spawn_file_actions_addopen attribute_hidden;
+
 __typeof (posix_spawn_file_actions_destroy)
   __posix_spawn_file_actions_destroy attribute_hidden;
 
diff --git a/posix/spawn_faction_addopen.c b/posix/spawn_faction_addopen.c
index d5694ee4d7..4fd64bb005 100644
--- a/posix/spawn_faction_addopen.c
+++ b/posix/spawn_faction_addopen.c
@@ -25,9 +25,9 @@
 /* Add an action to FILE-ACTIONS which tells the implementation to call
    `open' for the given file during the `spawn' call.  */
 int
-posix_spawn_file_actions_addopen (posix_spawn_file_actions_t *file_actions,
-				  int fd, const char *path, int oflag,
-				  mode_t mode)
+__posix_spawn_file_actions_addopen (posix_spawn_file_actions_t *file_actions,
+				    int fd, const char *path, int oflag,
+				    mode_t mode)
 {
   struct __spawn_action *rec;
 
@@ -60,3 +60,5 @@ posix_spawn_file_actions_addopen (posix_spawn_file_actions_t *file_actions,
 
   return 0;
 }
+weak_alias (__posix_spawn_file_actions_addopen,
+	    posix_spawn_file_actions_addopen)
diff --git a/posix/wordexp-test.c b/posix/wordexp-test.c
index a4d8bcf1da..7cbac030ab 100644
--- a/posix/wordexp-test.c
+++ b/posix/wordexp-test.c
@@ -15,19 +15,19 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <sys/stat.h>
-#include <sys/types.h>
-#include <sys/mman.h>
+#include <wordexp.h>
+#include <stdio.h>
 #include <fcntl.h>
-#include <unistd.h>
 #include <pwd.h>
-#include <stdio.h>
-#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
-#include <wordexp.h>
+#include <sys/mman.h>
+
 #include <libc-pointer-arith.h>
-#include <dso_handle.h>
+#include <array_length.h>
+#include <support/xunistd.h>
+#include <support/check.h>
+#include <support/next_to_fault.h>
 
 #define IFS " \n\t"
 
@@ -40,7 +40,7 @@ struct test_case_struct
   size_t wordc;
   const char *wordv[10];
   const char *ifs;
-} test_case[] =
+} static test_case[] =
   {
     /* Simple word- and field-splitting */
     { 0, NULL, "one", 0, 1, { "one", }, IFS },
@@ -213,8 +213,6 @@ struct test_case_struct
     { WRDE_SYNTAX, NULL, "`\\", 0, 0, { NULL, }, IFS },     /* BZ 18042  */
     { WRDE_SYNTAX, NULL, "${", 0, 0, { NULL, }, IFS },      /* BZ 18043  */
     { WRDE_SYNTAX, NULL, "L${a:", 0, 0, { NULL, }, IFS },   /* BZ 18043#c4  */
-
-    { -1, NULL, NULL, 0, 0, { NULL, }, IFS },
   };
 
 static int testit (struct test_case_struct *tc);
@@ -226,21 +224,19 @@ command_line_test (const char *words)
   wordexp_t we;
   int i;
   int retval = wordexp (words, &we, 0);
-  printf ("wordexp returned %d\n", retval);
+  printf ("info: wordexp returned %d\n", retval);
   for (i = 0; i < we.we_wordc; i++)
-    printf ("we_wordv[%d] = \"%s\"\n", i, we.we_wordv[i]);
+    printf ("info: we_wordv[%d] = \"%s\"\n", i, we.we_wordv[i]);
 }
 
-int
-main (int argc, char *argv[])
+static int
+do_test (int argc, char *argv[])
 {
-  const char *globfile[] = { "one", "two", "three", NULL };
+  const char *globfile[] = { "one", "two", "three" };
   char tmpdir[32];
   struct passwd *pw;
   const char *cwd;
   int test;
-  int fail = 0;
-  int i;
   struct test_case_struct ts;
 
   if (argc > 1)
@@ -253,21 +249,18 @@ main (int argc, char *argv[])
 
   /* Set up arena for pathname expansion */
   tmpnam (tmpdir);
-  if (mkdir (tmpdir, S_IRWXU) || chdir (tmpdir))
-    return -1;
-  else
-    {
-      int fd;
+  xmkdir (tmpdir, S_IRWXU);
+  TEST_VERIFY_EXIT (chdir (tmpdir) == 0);
 
-      for (i = 0; globfile[i]; ++i)
-	if ((fd = creat (globfile[i], S_IRUSR | S_IWUSR)) == -1
-	    || close (fd))
-	  return -1;
+  for (int i = 0; i < array_length (globfile); ++i)
+    {
+      int fd = xopen (globfile[i], O_WRONLY|O_CREAT|O_TRUNC,
+		      S_IRUSR | S_IWUSR);
+      xclose (fd);
     }
 
-  for (test = 0; test_case[test].retval != -1; test++)
-    if (testit (&test_case[test]))
-      ++fail;
+  for (test = 0; test < array_length (test_case); test++)
+    TEST_COMPARE (testit (&test_case[test]), 0);
 
   /* Tilde-expansion tests. */
   pw = getpwnam ("root");
@@ -281,8 +274,7 @@ main (int argc, char *argv[])
       ts.wordv[0] = pw->pw_dir;
       ts.ifs = IFS;
 
-      if (testit (&ts))
-	++fail;
+      TEST_COMPARE (testit (&ts), 0);
 
       ts.retval = 0;
       ts.env = pw->pw_dir;
@@ -292,8 +284,7 @@ main (int argc, char *argv[])
       ts.wordv[0] = "x";
       ts.ifs = IFS;
 
-      if (testit (&ts))
-	++fail;
+      TEST_COMPARE (testit (&ts), 0);
     }
 
   /* "~" expands to value of $HOME when HOME is set */
@@ -308,8 +299,7 @@ main (int argc, char *argv[])
   ts.wordv[1] = "/dummy/home/foo";
   ts.ifs = IFS;
 
-  if (testit (&ts))
-    ++fail;
+  TEST_COMPARE (testit (&ts), 0);
 
   /* "~" expands to home dir from passwd file if HOME is not set */
 
@@ -325,14 +315,13 @@ main (int argc, char *argv[])
       ts.wordv[0] = pw->pw_dir;
       ts.ifs = IFS;
 
-      if (testit (&ts))
-	++fail;
+      TEST_COMPARE (testit (&ts), 0);
     }
 
   puts ("tests completed, now cleaning up");
 
   /* Clean up */
-  for (i = 0; globfile[i]; ++i)
+  for (int i = 0; i < array_length (globfile); ++i)
     remove (globfile[i]);
 
   if (cwd == NULL)
@@ -341,33 +330,20 @@ main (int argc, char *argv[])
   chdir (cwd);
   rmdir (tmpdir);
 
-  printf ("tests failed: %d\n", fail);
-
-  return fail != 0;
+  return 0;
 }
 
-static const char *
+struct support_next_to_fault
 at_page_end (const char *words)
 {
-  const int pagesize = getpagesize ();
-  char *start = mmap (0, 2 * pagesize, PROT_READ|PROT_WRITE,
-		      MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
-
-  if (start == MAP_FAILED)
-    return start;
-
-  if (mprotect (start + pagesize, pagesize, PROT_NONE))
-    {
-      munmap (start, 2 * pagesize);
-      return MAP_FAILED;
-    }
+  const size_t words_size = strlen (words) + 1;
+  struct support_next_to_fault ntf
+    = support_next_to_fault_allocate (words_size);
 
   /* Includes terminating NUL.  */
-  const size_t words_size = strlen (words) + 1;
-  char *words_start = start + pagesize - words_size;
-  memcpy (words_start, words, words_size);
+  memcpy (ntf.buffer, words, words_size);
 
-  return words_start;
+  return ntf;
 }
 
 static int
@@ -395,20 +371,20 @@ testit (struct test_case_struct *tc)
   sav_we.we_offs = 3;
   we = sav_we;
 
-  printf ("Test %d (%s): ", ++tests, tc->words);
+  printf ("info: test %d (%s): ", ++tests, tc->words);
   fflush (NULL);
-  const char *words = at_page_end (tc->words);
+  struct support_next_to_fault words = at_page_end (tc->words);
 
   if (tc->flags & WRDE_APPEND)
     {
       /* initial wordexp() call, to be appended to */
       if (wordexp ("pre1 pre2", &we, tc->flags & ~WRDE_APPEND) != 0)
         {
-	  printf ("FAILED setup\n");
+	  printf ("info: FAILED setup\n");
 	  return 1;
 	}
     }
-  retval = wordexp (words, &we, tc->flags);
+  retval = wordexp (words.buffer, &we, tc->flags);
 
   if (tc->flags & WRDE_DOOFFS)
       start_offs = sav_we.we_offs;
@@ -436,7 +412,7 @@ testit (struct test_case_struct *tc)
   if (bzzzt)
     {
       printf ("FAILED\n");
-      printf ("Test words: <%s>, need retval %d, wordc %Zd\n",
+      printf ("info: Test words: <%s>, need retval %d, wordc %Zd\n",
 	      tc->words, tc->retval, tc->wordc);
       if (start_offs != 0)
 	printf ("(preceded by %d NULLs)\n", start_offs);
@@ -465,12 +441,11 @@ testit (struct test_case_struct *tc)
   if (retval == 0 || retval == WRDE_NOSPACE)
     wordfree (&we);
 
-  const int page_size = getpagesize ();
-  char *start = (char *) PTR_ALIGN_DOWN (words, page_size);
-
-  if (munmap (start, 2 * page_size) != 0)
-    return 1;
+  support_next_to_fault_free (&words);
 
   fflush (NULL);
   return bzzzt;
 }
+
+#define TEST_FUNCTION_ARGV do_test
+#include <support/test-driver.c>
diff --git a/posix/wordexp.c b/posix/wordexp.c
index 6a6e3a8e11..2aa6085fb2 100644
--- a/posix/wordexp.c
+++ b/posix/wordexp.c
@@ -25,33 +25,18 @@
 #include <libintl.h>
 #include <paths.h>
 #include <pwd.h>
-#include <signal.h>
 #include <stdbool.h>
 #include <stdio.h>
-#include <stdlib.h>
 #include <string.h>
 #include <sys/param.h>
-#include <sys/stat.h>
-#include <sys/time.h>
-#include <sys/types.h>
-#include <sys/types.h>
 #include <sys/wait.h>
 #include <unistd.h>
-#include <wchar.h>
 #include <wordexp.h>
-#include <kernel-features.h>
+#include <spawn.h>
 #include <scratch_buffer.h>
-
-#include <libc-lock.h>
 #include <_itoa.h>
-
-/* Undefine the following line for the production version.  */
-/* #define NDEBUG 1 */
 #include <assert.h>
 
-/* Get some device information.  */
-#include <device-nrs.h>
-
 /*
  * This is a recursive-descent-style word expansion routine.
  */
@@ -812,61 +797,76 @@ parse_arith (char **word, size_t *word_length, size_t *max_length,
   return WRDE_SYNTAX;
 }
 
+#define DYNARRAY_STRUCT        strlist
+#define DYNARRAY_ELEMENT       char *
+#define DYNARRAY_PREFIX        strlist_
+/* Allocates about 512/1024 (32/64 bit) on stack.  */
+#define DYNARRAY_INITIAL_SIZE  128
+#include <malloc/dynarray-skeleton.c>
+
 /* Function called by child process in exec_comm() */
-static inline void
-__attribute__ ((always_inline))
-exec_comm_child (char *comm, int *fildes, int showerr, int noexec)
+static pid_t
+exec_comm_child (char *comm, int *fildes, bool showerr, bool noexec)
 {
-  const char *args[4] = { _PATH_BSHELL, "-c", comm, NULL };
+  pid_t pid = -1;
 
-  /* Execute the command, or just check syntax? */
-  if (noexec)
-    args[1] = "-nc";
+  /* Execute the command, or just check syntax?  */
+  const char *args[] = { _PATH_BSHELL, noexec ? "-nc" : "-c", comm, NULL };
+
+  posix_spawn_file_actions_t fa;
+  /* posix_spawn_file_actions_init does not fail.  */
+  __posix_spawn_file_actions_init (&fa);
 
-  /* Redirect output.  */
-  if (__glibc_likely (fildes[1] != STDOUT_FILENO))
+  /* Redirect output.  For check syntax only (noexec being true), exec_comm
+     explicits sets fildes[1] to -1, so check its value to avoid a failure in
+     __posix_spawn_file_actions_adddup2.  */
+  if (fildes[1] != -1)
     {
-      __dup2 (fildes[1], STDOUT_FILENO);
-      __close (fildes[1]);
+      if (__glibc_likely (fildes[1] != STDOUT_FILENO))
+	{
+	  if (__posix_spawn_file_actions_adddup2 (&fa, fildes[1],
+						  STDOUT_FILENO) != 0
+	      || __posix_spawn_file_actions_addclose (&fa, fildes[1]) != 0)
+	    goto out;
+	}
+      else
+	/* Reset the close-on-exec flag (if necessary).  */
+	if (__posix_spawn_file_actions_adddup2 (&fa, fildes[1], fildes[1])
+	    != 0)
+	  goto out;
     }
-  else
-    /* Reset the close-on-exec flag (if necessary).  */
-    __fcntl (fildes[1], F_SETFD, 0);
 
   /* Redirect stderr to /dev/null if we have to.  */
-  if (showerr == 0)
+  if (!showerr)
+    if (__posix_spawn_file_actions_addopen (&fa, STDERR_FILENO, _PATH_DEVNULL,
+					    O_WRONLY, 0) != 0)
+      goto out;
+
+  struct strlist newenv;
+  strlist_init (&newenv);
+
+  bool recreate_env = getenv ("IFS") != NULL;
+  if (recreate_env)
     {
-      struct stat64 st;
-      int fd;
-      __close (STDERR_FILENO);
-      fd = __open (_PATH_DEVNULL, O_WRONLY);
-      if (fd >= 0 && fd != STDERR_FILENO)
-	{
-	  __dup2 (fd, STDERR_FILENO);
-	  __close (fd);
-	}
-      /* Be paranoid.  Check that we actually opened the /dev/null
-	 device.  */
-      if (__builtin_expect (__fxstat64 (_STAT_VER, STDERR_FILENO, &st), 0) != 0
-	  || __builtin_expect (S_ISCHR (st.st_mode), 1) == 0
-#if defined DEV_NULL_MAJOR && defined DEV_NULL_MINOR
-	  || st.st_rdev != __gnu_dev_makedev (DEV_NULL_MAJOR, DEV_NULL_MINOR)
-#endif
-	  )
-	/* It's not the /dev/null device.  Stop right here.  The
-	   problem is: how do we stop?  We use _exit() with an
-	   hopefully unusual exit code.  */
-	_exit (90);
+      for (char **ep = __environ; *ep != NULL; ep++)
+	if (strncmp (*ep, "IFS=", strlen ("IFS=")) != 0)
+	  strlist_add (&newenv, *ep);
+      strlist_add (&newenv, NULL);
+      if (strlist_has_failed (&newenv))
+	goto out;
     }
 
-  /* Make sure the subshell doesn't field-split on our behalf. */
-  __unsetenv ("IFS");
+  /* pid is not set if posix_spawn fails, so it keep the original value
+     of -1.  */
+  __posix_spawn (&pid, _PATH_BSHELL, &fa, NULL, (char *const *) args,
+		 recreate_env ? strlist_begin (&newenv) : __environ);
 
-  __close (fildes[0]);
-  __execve (_PATH_BSHELL, (char *const *) args, __environ);
+  strlist_free (&newenv);
+
+out:
+  __posix_spawn_file_actions_destroy (&fa);
 
-  /* Bad.  What now?  */
-  abort ();
+  return pid;
 }
 
 /* Function to execute a command and retrieve the results */
@@ -884,13 +884,13 @@ exec_comm (char *comm, char **word, size_t *word_length, size_t *max_length,
   size_t maxnewlines = 0;
   char buffer[bufsize];
   pid_t pid;
-  int noexec = 0;
+  bool noexec = false;
 
   /* Do nothing if command substitution should not succeed.  */
   if (flags & WRDE_NOCMD)
     return WRDE_CMDSUB;
 
-  /* Don't fork() unless necessary */
+  /* Don't posix_spawn unless necessary */
   if (!comm || !*comm)
     return 0;
 
@@ -898,19 +898,15 @@ exec_comm (char *comm, char **word, size_t *word_length, size_t *max_length,
     return WRDE_NOSPACE;
 
  again:
-  if ((pid = __fork ()) < 0)
+  pid = exec_comm_child (comm, fildes, noexec ? false : flags & WRDE_SHOWERR,
+			 noexec);
+  if (pid < 0)
     {
-      /* Bad */
       __close (fildes[0]);
       __close (fildes[1]);
       return WRDE_NOSPACE;
     }
 
-  if (pid == 0)
-    exec_comm_child (comm, fildes, noexec ? 0 : flags & WRDE_SHOWERR, noexec);
-
-  /* Parent */
-
   /* If we are just testing the syntax, only wait.  */
   if (noexec)
     return (TEMP_FAILURE_RETRY (__waitpid (pid, &status, 0)) == pid
@@ -1091,7 +1087,7 @@ exec_comm (char *comm, char **word, size_t *word_length, size_t *max_length,
   /* Check for syntax error (re-execute but with "-n" flag) */
   if (buflen < 1 && status != 0)
     {
-      noexec = 1;
+      noexec = true;
       goto again;
     }
 
@@ -1143,26 +1139,9 @@ parse_comm (char **word, size_t *word_length, size_t *max_length,
 	      /* Go -- give script to the shell */
 	      if (comm)
 		{
-#ifdef __libc_ptf_call
-		  /* We do not want the exec_comm call to be cut short
-		     by a thread cancellation since cleanup is very
-		     ugly.  Therefore disable cancellation for
-		     now.  */
-		  // XXX Ideally we do want the thread being cancelable.
-		  // XXX If demand is there we'll change it.
-		  int state = PTHREAD_CANCEL_ENABLE;
-		  __libc_ptf_call (__pthread_setcancelstate,
-				   (PTHREAD_CANCEL_DISABLE, &state), 0);
-#endif
-
+		  /* posix_spawn already handles thread cancellation.  */
 		  error = exec_comm (comm, word, word_length, max_length,
 				     flags, pwordexp, ifs, ifs_white);
-
-#ifdef __libc_ptf_call
-		  __libc_ptf_call (__pthread_setcancelstate,
-				   (state, NULL), 0);
-#endif
-
 		  free (comm);
 		}