glibc/sysdeps/unix/sysv/linux/fexecve.c

/* Copyright (C) 1994-2021 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 <errno.h>
#include <stddef.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>

#include <sysdep.h>
#include <sys/syscall.h>
#include <kernel-features.h>


/* Execute the file FD refers to, overlaying the running program image.
   ARGV and ENVP are passed to the new program, as for `execve'.  */
int
fexecve (int fd, char *const argv[], char *const envp[])
{
  if (fd < 0 || argv == NULL || envp == NULL)
    {
      __set_errno (EINVAL);
      return -1;
    }

#ifdef __NR_execveat
  /* Avoid implicit array coercion in syscall macros.  */
  INLINE_SYSCALL (execveat, 5, fd, "", &argv[0], &envp[0], AT_EMPTY_PATH);
# ifndef __ASSUME_EXECVEAT
  if (errno != ENOSYS)
    return -1;
# endif
#endif

#ifndef __ASSUME_EXECVEAT
  /* We use the /proc filesystem to get the information.  If it is not
     mounted we fail.  */
  char buf[sizeof "/proc/self/fd/" + sizeof (int) * 3];
  __snprintf (buf, sizeof (buf), "/proc/self/fd/%d", fd);

  /* We do not need the return value.  */
  __execve (buf, argv, envp);

  int save = errno;

  /* We come here only if the 'execve' call fails.  Determine whether
     /proc is mounted.  If not we return ENOSYS.  */
  struct stat64 st;
  if (__stat64 ("/proc/self/fd", &st) != 0 && errno == ENOENT)
    save = ENOSYS;

  __set_errno (save);
#endif

  return -1;
}