linux: Add execveat system call wrapper

It operates similar to execve and it is is already used to implement
fexecve without requiring /proc to be mounted.  However, different
than fexecve, if the syscall is not supported by the kernel an error
is returned instead of trying a fallback.

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

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

1 files changed, 183 insertions, 0 deletions

diff --git a/posix/tst-execveat.c b/posix/tst-execveat.c
new file mode 100644
index 0000000000..53178c10d5
--- /dev/null
+++ b/posix/tst-execveat.c
@@ -0,0 +1,183 @@
+/* Test execveat at the various corner cases.
+   Copyright (C) 2021 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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <fcntl.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <dirent.h>
+#include <support/check.h>
+#include <support/support.h>
+#include <support/temp_file.h>
+#include <support/xdlfcn.h>
+#include <support/xstdio.h>
+#include <support/xunistd.h>
+#include <wait.h>
+#include <support/test-driver.h>
+
+int
+call_execveat (int fd, const char *pathname, int flags, int expected_fail,
+               int num)
+{
+  char *envp[] = { (char *) "FOO=3", NULL };
+  char *argv[] = { (char *) "sh", (char *) "-c", (char *) "exit $FOO", NULL };
+  pid_t pid;
+  int status;
+
+  if (test_verbose > 0)
+    printf ("call line number: %d\n", num);
+
+  pid = xfork ();
+  if (pid == 0)
+    {
+      TEST_COMPARE (execveat (fd, pathname, argv, envp, flags), -1);
+      if (errno == ENOSYS)
+	exit (EXIT_UNSUPPORTED);
+      else if (errno == expected_fail)
+        {
+          if (test_verbose > 0)
+            printf ("expected fail: errno %d\n", errno);
+          _exit (0);
+        }
+      else
+        FAIL_EXIT1 ("execveat failed: %m (%d)", errno);
+    }
+  xwaitpid (pid, &status, 0);
+
+  if (!WIFEXITED (status))
+    FAIL_RET ("child hasn't exited normally");
+
+  if (WIFEXITED (status))
+    {
+      if (WEXITSTATUS (status) == EXIT_UNSUPPORTED)
+        FAIL_UNSUPPORTED ("execveat is unimplemented");
+      else if (expected_fail != 0)
+        TEST_COMPARE (WEXITSTATUS (status), 0);
+      else
+        TEST_COMPARE (WEXITSTATUS (status), 3);
+    }
+  return 0;
+}
+
+static int
+do_test (void)
+{
+  DIR *dirp;
+  int fd, fd_out;
+  char *tmp_dir, *symlink_name, *tmp_sh;
+  struct stat64 st;
+
+  dirp = opendir ("/bin");
+  if (dirp == NULL)
+    FAIL_EXIT1 ("failed to open /bin");
+  fd = dirfd (dirp);
+
+  /* Call execveat for various fd/pathname combinations.  */
+
+  /* Check the pathname relative to a valid dirfd.  */
+  call_execveat (fd, "sh", 0, 0, __LINE__);
+  xchdir ("/bin");
+  /* Use the special value AT_FDCWD as dirfd. Quoting open(2):
+     If pathname is relative and dirfd is the special value AT_FDCWD, then
+     pathname is interpreted relative to the current working directory of
+     the calling process.  */
+  call_execveat (AT_FDCWD, "sh", 0, 0, __LINE__);
+  xclose (fd);
+#ifdef O_PATH
+  /* Check the pathname relative to a valid dirfd with O_PATH.  */
+  fd = xopen ("/bin", O_PATH | O_DIRECTORY, O_RDONLY);
+  call_execveat (fd, "sh", 0, 0, __LINE__);
+  xclose (fd);
+
+  /* Check absolute pathname, dirfd should be ignored.  */
+  call_execveat (AT_FDCWD, "/bin/sh", 0, 0, __LINE__);
+  fd = xopen ("/usr", O_PATH | O_DIRECTORY, 0);
+  /* Same check for absolute pathname, but with input file descriptor
+     openend with different flags.  The dirfd should be ignored.  */
+  call_execveat (fd, "/bin/sh", 0, 0, __LINE__);
+  xclose (fd);
+#endif
+
+  fd = xopen ("/usr", O_RDONLY, 0);
+  /* Same check for absolute pathname, but with input file descriptor
+     openend with different flags.  The dirfd should be ignored.  */
+  call_execveat (fd, "/bin/sh", 0, 0, __LINE__);
+  xclose (fd);
+
+  fd = xopen ("/bin/sh", O_RDONLY, 0);
+  /* Check relative pathname, where dirfd does not point to a directory.  */
+  call_execveat (fd, "sh", 0, ENOTDIR, __LINE__);
+  /* Check absolute pathname, but dirfd is a regular file.  The dirfd
+     should be ignored.  */
+  call_execveat (fd, "/bin/sh", 0, 0, __LINE__);
+  xclose (fd);
+
+#ifdef O_PATH
+  /* Quoting open(2): O_PATH
+     Obtain a file descriptor that can be used for two purposes: to
+     indicate a location in the filesystem tree and to perform
+     operations that act purely at the file descriptor level.  */
+  fd = xopen ("/bin/sh", O_PATH, 0);
+  /* Check the empty pathname.  Dirfd is a regular file with O_PATH.  */
+  call_execveat (fd, "", 0, ENOENT, __LINE__);
+  /* Same check for an empty pathname, but with AT_EMPTY_PATH flag.
+     Quoting open(2):
+     If oldpath is an empty string, create a link to the file referenced
+     by olddirfd (which may have been obtained using the open(2) O_PATH flag. */
+  call_execveat (fd, "", AT_EMPTY_PATH, 0, __LINE__);
+  call_execveat (fd, "", AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW, 0, __LINE__);
+  xclose (fd);
+
+  /* Create a temporary directory "tmp_dir" and create a symbolik link tmp_sh
+     pointing to /bin/sh inside the tmp_dir. Open dirfd as a symbolic link.  */
+  tmp_dir = support_create_temp_directory ("tst-execveat_dir");
+  symlink_name = xasprintf ("%s/symlink", tmp_dir);
+  xsymlink ("tmp_sh", symlink_name);
+  add_temp_file (symlink_name);
+  tmp_sh = xasprintf ("%s/tmp_sh", tmp_dir);
+  add_temp_file (tmp_sh);
+  fd_out = xopen (symlink_name, O_CREAT | O_WRONLY, 0);
+  xstat ("/bin/sh", &st);
+  fd = xopen ("/bin/sh", O_RDONLY, 0);
+  xcopy_file_range (fd, 0, fd_out, 0, st.st_size, 0);
+  xfchmod (fd_out, 0700);
+  xclose (fd);
+  xclose (fd_out);
+  fd_out = xopen (symlink_name, O_PATH, 0);
+
+ /* Check the empty pathname. Dirfd is a symbolic link.  */
+  call_execveat (fd_out, "", 0, ENOENT, __LINE__);
+  call_execveat (fd_out, "", AT_EMPTY_PATH, 0, __LINE__);
+  call_execveat (fd_out, "", AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW, 0,
+                 __LINE__);
+  xclose (fd_out);
+  free (symlink_name);
+  free (tmp_sh);
+  free (tmp_dir);
+#endif
+
+  /* Call execveat with closed fd, we expect this to fail with EBADF.  */
+  call_execveat (fd, "sh", 0, EBADF, __LINE__);
+  /* Call execveat with closed fd, we expect this to pass because the pathname is
+     absolute.  */
+  call_execveat (fd, "/bin/sh", 0, 0, __LINE__);
+
+  return 0;
+}
+
+#include <support/test-driver.c>