[PATCH v5] init: Disable defaults if init= fails

Andy Lutomirski
2014-09-29T02:40:37Z

If a user puts init=/whatever on the command line and /whatever
can't be run, then the kernel will try a few default options before
giving up. If init=/whatever came from a bootloader prompt, then
this is unexpected but probably harmless. On the other hand, if it
comes from a script (e.g. a tool like virtme or perhaps a future
kselftest script), then the fallbacks are likely to exist, but
they'll do the wrong thing. For example, they might unexpectedly
invoke systemd.

This makes a failure to run the specified init= process be fatal.

As a temporary measure, users can set CONFIG_INIT_FALLBACK=y to
preserve the old behavior. If no one speaks up, we can remove that
option entirely after a release or two.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
---

Changes from v4:
- Update the panic message (sorry for the noise)

Changes from v3:
- Get rid of the strictinit option. Now the new behavior is the default
unless CONFIG_INIT_FALLBACK=y (Rob Landley)

Changes from v2:
- Improve docs further, to leave the door open to giving strictinit
some sensible semantics if init= is not set.
- Improve error output in the failure case (Shuah Khan).

Changes from v1:
- Add missing "if" to the docs (Randy Dunlap)

init/Kconfig | 11 +++++++++++
init/main.c | 7 ++++++-
2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/init/Kconfig b/init/Kconfig
index e84c6423a2e5..063029a1556f 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1299,6 +1299,17 @@ source "usr/Kconfig"

endif

+config INIT_FALLBACK
+ bool "Fall back to defaults if init= parameter is bad"
+ help
+ If enabled, the kernel will try the default init binaries if an
+ explicit request from the init= parameter fails.
+
+ This is a temporary measure to allow broken configurations
+ to continue to boot.
+
+ If unsure, say N.
+
config CC_OPTIMIZE_FOR_SIZE
bool "Optimize for size"
help
diff --git a/init/main.c b/init/main.c
index bb1aed928f21..2bd6105e5dc5 100644
--- a/init/main.c
+++ b/init/main.c
@@ -960,8 +960,13 @@ static int __ref kernel_init(void *unused)
ret = run_init_process(execute_command);
if (!ret)
return 0;
+#ifndef CONFIG_INIT_FALLBACK
+ panic("Requested init %s failed (error %d).",
+ execute_command, ret);
+#else
pr_err("Failed to execute %s (error %d). Attempting defaults...\n",
- execute_command, ret);
+ execute_command, ret);
+#endif
}
if (!try_to_run_init_process("/sbin/init") ||
!try_to_run_init_process("/etc/init") ||
--
1.9.3