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

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Date:	Fri, 26 Sep 2014 12:31:54 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Chuck Ebbert <cebbert.lkml@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.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, Sep 26, 2014 at 12:23 PM, Chuck Ebbert <cebbert.lkml@...il.com> wrote:
> 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?

I don't think so.  Old kernels will wonder why "foo,strict" doesn't exist.

-- 
Andy Lutomirski
AMA Capital Management, LLC
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