linux-kernel - Re: The policy on initramfs decompression failure

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Date:	Wed, 14 Jan 2009 00:42:17 +0100
From:	Bodo Eggert <7eggert@....de>
To:	"H. Peter Anvin" <hpa@...or.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Al Viro <viro@....linux.org.uk>, Alain Knaff <alain@...ff.lu>
Subject: Re: The policy on initramfs decompression failure

H. Peter Anvin <hpa@...or.com> wrote:

[initramfs decryption failed]

> I had personally assumed the proper policy would be to panic, since it
> is unlikely to mean the system can be booted.  However, Ingo brought up
> the case where the initramfs is auxilliary to being able to boot the
> full system, for example the initramfs supplied is primarily a data
> carrier, and either the builtin initramfs or the kernel itself is
> sufficient to boot.
> 
> By this argument, we should change initramfs decoding failure to a
> KERN_CRIT message, and in the (presumably most common) case that it does
> not suffice to boot the system, we will get a panic in short order as
> the system is unable to find init.
> 
> This argument seems to mostly hold water, but it does implement a policy
> change over the current code.  Furthermore, it does make me concerned
> that a *partial* decoding failure (such as can be caused by a corrupt
> image, or, say, a gzipped image concatenated to a bzip2 image, with the
> kernel only supporting bzip2) could cause a booted-but-dysfunctional
> system, which is in many configurations a worse failure mode than a panic.

If the initrd is not decompressed successfully, and if it's not there for fun,
the system boot will be most likely fubar, and at worst a wrong system or a
less secured configuration may be started. Therefore I'd create a kernel
option. Possible values would be e.g. [*panic,continue] or 
[*auto|required|optional|ignore], with:

panic, continue: As expected
auto: If there is an initrd, it's required, otherwise it's ignored
required: Panic if the initrd did not exist or was not unpacked correctly
optional: Like continue
ignore: Don't load the initrd
*: Default value

I currently don't know how to name the option.

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