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117 lines
2.9 KiB
117 lines
2.9 KiB
/* switch_root.c - Switch from rootfs/initramfs to another filesystem
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*
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* Copyright 2005 Rob Landley <rob@landley.net>
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USE_SWITCH_ROOT(NEWTOY(switch_root, "<2c:h", TOYFLAG_SBIN))
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config SWITCH_ROOT
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bool "switch_root"
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default y
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help
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usage: switch_root [-c /dev/console] NEW_ROOT NEW_INIT...
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Use from PID 1 under initramfs to free initramfs, chroot to NEW_ROOT,
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and exec NEW_INIT.
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-c Redirect console to device in NEW_ROOT
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-h Hang instead of exiting on failure (avoids kernel panic)
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*/
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#define FOR_switch_root
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#include "toys.h"
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#include <sys/vfs.h>
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GLOBALS(
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char *c;
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dev_t rootdev;
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)
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static int del_node(struct dirtree *node)
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{
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if (node->st.st_dev == TT.rootdev && dirtree_notdotdot(node)) {
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int flag = 0;
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if (S_ISDIR(node->st.st_mode)) {
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if (!node->again) return DIRTREE_COMEAGAIN;
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flag = AT_REMOVEDIR;
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}
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unlinkat(dirtree_parentfd(node), node->name, flag);
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}
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return 0;
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}
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void switch_root_main(void)
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{
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char *newroot = *toys.optargs, **cmdline = toys.optargs+1;
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struct stat st1, st2;
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struct statfs stfs;
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int console = console; // gcc's "may be used" warnings are broken.
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if (getpid() != 1) error_exit("not pid 1");
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// Root filesystem we're leaving must be ramfs or tmpfs
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if (statfs("/", &stfs) ||
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(stfs.f_type != 0x858458f6 && stfs.f_type != 0x01021994))
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{
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error_msg("not ramfs");
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goto panic;
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}
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// New directory must be different filesystem instance
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if (chdir(newroot) || stat(".", &st1) || stat("/", &st2) ||
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st1.st_dev == st2.st_dev)
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{
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error_msg("bad newroot '%s'", newroot);
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goto panic;
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}
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TT.rootdev=st2.st_dev;
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// trim any / characters from the init cmdline, as we want to test it with
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// stat(), relative to newroot. *cmdline is also used below, but by that
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// point we are in the chroot, so a relative path is still OK.
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while (**cmdline == '/') (*cmdline)++;
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// init program must exist and be an executable file
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if (stat(*cmdline, &st1) || !S_ISREG(st1.st_mode) || !(st1.st_mode&0100)) {
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error_msg("bad init");
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goto panic;
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}
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if (TT.c && -1 == (console = open(TT.c, O_RDWR))) {
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perror_msg("bad console '%s'", TT.c);
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goto panic;
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}
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// Ok, enough safety checks: wipe root partition.
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dirtree_read("/", del_node);
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// Fix the appearance of the mount table in the newroot chroot
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if (mount(".", "/", NULL, MS_MOVE, NULL)) {
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perror_msg("mount");
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goto panic;
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}
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// Enter the new root before starting init
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if (chroot(".")) {
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perror_msg("chroot");
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goto panic;
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}
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// Make sure cwd does not point outside of the chroot
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if (chdir("/")) {
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perror_msg("chdir");
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goto panic;
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}
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if (TT.c) {
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int i;
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for (i=0; i<3; i++) if (console != i) dup2(console, i);
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if (console>2) close(console);
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}
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execv(*cmdline, cmdline);
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perror_msg("Failed to exec '%s'", *cmdline);
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panic:
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if (toys.optflags & FLAG_h) for (;;) wait(NULL);
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}
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