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init: allow CONFIG_INIT_FALLBACK=n to disable defaults if init= fails

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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 adds a config option CONFIG_INIT_FALLBACK.  If unset, then a failure
to run the specified init= process be fatal.

The tentative plan is to remove CONFIG_INIT_FALLBACK for 3.20.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Cc: Rob Landley <rob@landley.net>
Cc: Chuck Ebbert <cebbert.lkml@gmail.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Shuah Khan <shuah.kh@samsung.com>
Cc: Frank Rowand <frowand.list@gmail.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andy Lutomirski 2014-12-10 15:52:19 -08:00 committed by Linus Torvalds
parent 52f5592e54
commit 6ef4536e2f
2 changed files with 22 additions and 1 deletions
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16
init/Kconfig
View File

@ -1280,6 +1280,22 @@ source "usr/Kconfig"
endif
config INIT_FALLBACK
bool "Fall back to defaults if init= parameter is bad"
default y
help
If enabled, the kernel will try the default init binaries if an
explicit request from the init= parameter fails.
This can have unexpected effects. For example, booting
with init=/sbin/kiosk_app will run /sbin/init or even /bin/sh
if /sbin/kiosk_app cannot be executed.
The default value of Y is consistent with historical behavior.
Selecting N is likely to be more appropriate for most uses,
especially on kiosks and on kernels that are intended to be
run under the control of a script.
config CC_OPTIMIZE_FOR_SIZE
bool "Optimize for size"
help

7
init/main.c
View File

@ -952,8 +952,13 @@ 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") ||