Fix switch_root implementation.
Add the MS_MOVE of cwd to / and chroot into it. chdir is also
called to ensure cwd does not point outside the chroot.
The switch_root toy was also blocking any case where NEW_ROOT/init
did not exist, even though NEW_INIT was a required parameter and
did not have to be '/init'. Change it to handle any NEW_INIT
passed as either a relative or absolute path.
With this change, the switch_root toy actually works from initramfs.
diff --git a/toys/other/switch_root.c b/toys/other/switch_root.c
index 0861c70..acbae2b 100644
--- a/toys/other/switch_root.c
+++ b/toys/other/switch_root.c
@@ -67,8 +67,13 @@
}
TT.rootdev=st2.st_dev;
+ // trim any / characters from the init cmdline, as we want to test it with
+ // stat(), relative to newroot. *cmdline is also used below, but by that
+ // point we are in the chroot, so a relative path is still OK.
+ while (**cmdline == '/') (*cmdline)++;
+
// init program must exist and be an executable file
- if (stat("init", &st1) || !S_ISREG(st1.st_mode) || !(st1.st_mode&0100)) {
+ if (stat(*cmdline, &st1) || !S_ISREG(st1.st_mode) || !(st1.st_mode&0100)) {
error_msg("bad init");
goto panic;
}
@@ -81,6 +86,24 @@
// Ok, enough safety checks: wipe root partition.
dirtree_read("/", del_node);
+ // Fix the appearance of the mount table in the newroot chroot
+ if (mount(".", "/", NULL, MS_MOVE, NULL)) {
+ perror_msg("mount");
+ goto panic;
+ }
+
+ // Enter the new root before starting init
+ if (chroot(".")) {
+ perror_msg("chroot");
+ goto panic;
+ }
+
+ // Make sure cwd does not point outside of the chroot
+ if (chdir("/")) {
+ perror_msg("chdir");
+ goto panic;
+ }
+
if (TT.console) {
int i;
for (i=0; i<3; i++) if (console != i) dup2(console, i);
