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bootstrap-initrd

Linux initrd to bootstrap from a small binary seed git clone https://anongit.hacktivis.me/git/bootstrap-initrd.git/

init.c (2686B)

    

  1. // bootstrap-initrd: Linux initrd to bootstrap from a small binary seed
  2. // SPDX-FileCopyrightText: 2017 Haelwenn (lanodan) Monnier <contact+utils@hacktivis.me>
  3. // SPDX-License-Identifier: MPL-2.0
  5. #define _POSIX_C_SOURCE 200809L
  6. #define _XOPEN_SOURCE 700 // mknod
  8. #include "src/oksh_tcc.h"
  10. #include <errno.h>
  11. #include <fcntl.h>  // O_RDONLY
  12. #include <spawn.h>  // posix_spawn
  13. #include <stdio.h>  // fprintf
  14. #include <stdlib.h> // setenv
  15. #include <string.h> // strerror
  16. #include <sys/mount.h>
  17. #include <sys/stat.h>      // mknod
  18. #include <sys/sysmacros.h> // makedev
  19. #include <sys/wait.h>      // waitpid
  20. #include <unistd.h>        // chdir, environ
  22. /* From SUS Chapter 8: Environment variable */
  23. extern char **environ;
  25. static int
  26. exec_wait(char *args[])
  27. {
  28. 	pid_t child = 0;
  29. 	// Allows to avoid a fork+exec
  30. 	int ret = posix_spawn(&child, args[0], NULL, NULL, args, environ);
  31. 	if(ret != 0)
  32. 	{
  33. 		fprintf(stderr, "Failed spawning command with argv[0] = '%s': %s\n", args[0], strerror(errno));
  34. 		return -1;
  35. 	}
  37. 	int stat;
  38. 	if(waitpid(child, &stat, 0) == -1)
  39. 	{
  40. 		fprintf(stderr, "Failed waiting for child of pid %d: %s\n", child, strerror(errno));
  41. 		return -1;
  42. 	}
  44. 	if(!WIFEXITED(stat))
  45. 	{
  46. 		fprintf(stderr, "'%s' did not exit normally\n", args[0]);
  47. 		return -1;
  48. 	}
  50. 	if(WEXITSTATUS(stat) != 0)
  51. 	{
  52. 		fprintf(stderr, "'%s' exited with code %d\n", args[0], WEXITSTATUS(stat));
  53. 		return -1;
  54. 	}
  56. 	return 0;
  57. }
  59. static int
  60. build_oksh()
  61. {
  62. 	chdir("/src/oksh-oksh-7.8");
  64. 	fprintf(stderr, "Compiling oksh-7.8\n");
  66. 	if(exec_wait(oksh_tcc_cmd) < 0) return -1;
  68. 	fprintf(stderr, "Compiled oksh !\n");
  70. 	return 0;
  71. }
  73. int
  74. main(int argc, char *argv[])
  75. {
  76. 	setenv("PATH", "/bin:/usr/bin:/usr/local/bin", 1);
  77. 	setenv("HOME", "/root", 1);
  78. 	setenv("LOGNAME", "root", 1);
  80. 	if(build_oksh() < 0) return 1;
  82. 	if(mount("sysfs", "/sys", "sysfs", MS_NOSUID | MS_NODEV | MS_NOEXEC | MS_RELATIME, NULL) < 0)
  83. 		fprintf(stderr, "Failed to mount /sys: %s\n", strerror(errno));
  85. 	if(mount("proc", "/proc", "proc", MS_NOSUID | MS_NODEV | MS_NOEXEC | MS_RELATIME, "hidepid=2") <
  86. 	   0)
  87. 		fprintf(stderr, "Failed to mount /proc: %s\n", strerror(errno));
  89. 	if(mount("devtmpfs", "/dev", "devtmpfs", MS_NOSUID | MS_NOEXEC, NULL) < 0)
  90. 		fprintf(stderr, "Failed to mount /proc: %s\n", strerror(errno));
  92. 	errno = 0;
  93. 	if(mknod("/dev/null", S_IFCHR | 0666, makedev(0x1, 0x3)) < 0)
  94. 	{
  95. 		if(errno != 0 && errno != EEXIST)
  96. 			fprintf(stderr, "Failed to create /dev/null: %s\n", strerror(errno));
  97. 	}
  99. 	fprintf(stderr, "Launching: /bin/oksh /init.sh\n");
  101. 	if(execl("/bin/oksh", "-sh", "/init.sh", (char *)0) < 0)
  102. 	{
  103. 		fprintf(stderr, "Failed to execute: %s\n", strerror(errno));
  104. 		return 1;
  105. 	}
  107. 	fprintf(stderr, "Unreachable\n");
  108. }