linux-kernel - Re: [PATCH v3] init: Add strictinit to disable init= fallbacks

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Date:	Fri, 26 Sep 2014 14:23:15 -0500
From:	Chuck Ebbert <cebbert.lkml@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>,
	Shuah Khan <shuah.kh@...sung.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH v3] init: Add strictinit to disable init= fallbacks

On Fri, 26 Sep 2014 12:13:57 -0700
Andy Lutomirski <luto@...capital.net> wrote:

> 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 probably makes sense.  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 new option called strictinit.  If init= and strictinit
> are both set, and the init= binary is not executable, then the
> kernel will panic immediately.  If strictinit is set but init= is
> not set, then strictinit will have no effect, because the only real
> alternative would be to panic regardless of the contents of the root
> fs.
> 
> Signed-off-by: Andy Lutomirski <luto@...capital.net>
> ---
>  Documentation/kernel-parameters.txt |  8 ++++++++
>  init/main.c                         | 16 ++++++++++++++--
>  2 files changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 10d51c2f10d7..1576273edce6 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -3236,6 +3236,14 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  	stifb=		[HW]
>  			Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
>  
> +	strictinit	[KNL,BOOT]
> +			Normally, if the kernel can't find the init binary
> +			specified by rdinit= and/or init=, then it will
> +			try several fallbacks.  If strictinit is set
> +			and the value specified by init= does not work,
> +			then the kernel will panic instead.
> +			This option makes no sense if init= is not specified.
> +
>  	sunrpc.min_resvport=
>  	sunrpc.max_resvport=
>  			[NFS,SUNRPC]
> diff --git a/init/main.c b/init/main.c
> index bb1aed928f21..2ae0f2776155 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -131,6 +131,7 @@ static char *initcall_command_line;
>  
>  static char *execute_command;
>  static char *ramdisk_execute_command;
> +static bool strictinit;
>  
>  /*
>   * Used to generate warnings if static_key manipulation functions are used
> @@ -347,6 +348,13 @@ static int __init rdinit_setup(char *str)
>  }
>  __setup("rdinit=", rdinit_setup);
>  
> +static int __init strictinit_setup(char *str)
> +{
> +	strictinit = true;
> +	return 1;
> +}
> +__setup("strictinit", strictinit_setup);
> +
>  #ifndef CONFIG_SMP
>  static const unsigned int setup_max_cpus = NR_CPUS;
>  #ifdef CONFIG_X86_LOCAL_APIC
> @@ -960,8 +968,12 @@ static int __ref kernel_init(void *unused)
>  		ret = run_init_process(execute_command);
>  		if (!ret)
>  			return 0;
> -		pr_err("Failed to execute %s (error %d).  Attempting defaults...\n",
> -			execute_command, ret);
> +		if (strictinit)
> +			panic("Requested init %s failed (error %d) and strictinit was set.",
> +			      execute_command, ret);
> +		else
> +			pr_err("Failed to execute %s (error %d).  Attempting defaults...\n",
> +			       execute_command, ret);
>  	}
>  	if (!try_to_run_init_process("/sbin/init") ||
>  	    !try_to_run_init_process("/etc/init") ||

Can't you just make it use "init=foo,strict" instead?
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