linux-kernel - Re: [RFC PATCH] initramfs: correctly handle space in path on cpio list generation

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Message-ID: <698b6ced.050a0220.9e34a.3e08@mx.google.com>
Date: Tue, 10 Feb 2026 18:37:44 +0100
From: Christian Marangi <ansuelsmth@...il.com>
To: David Disseldorp <ddiss@...e.de>
Cc: Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nsc@...nel.org>,
	Dmitry Safonov <0x7f454c46@...il.com>, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [RFC PATCH] initramfs: correctly handle space in path on cpio
 list generation

On Tue, Feb 10, 2026 at 10:34:31PM +1100, David Disseldorp wrote:
> [cc'ing fsdevel]
> 
> On Mon,  9 Feb 2026 16:37:58 +0100, Christian Marangi wrote:
> 
> > The current gen_initramfs.sh and gen_init_cpio.c tools doesn't correctly
> > handle path or filename with space in it. Although highly discouraged,
> 
> "highly discouraged" isn't really appropriate here; the kernel generally
> doesn't care whether or not a filename carries whitespace.
> The limitation here is specifically the gen_init_cpio manifest format,
> which is strictly space-separated.
>

Yes but the value space-separated was done only out of simplicity also with the
parsing in the .c tool not strictly a requirement for the actual cpio blob that
is then generated. The problem is in the intermediate file and I feel it should
be fixed or handled.
 
> > Linux also supports filename or path with whiespace and currently this
> > will produce error on generating and parsing the cpio_list file as the
> > pattern won't match the expected variables order. (with gid or mode
> > parsed as string)
> > 
> > This was notice when creating an initramfs with including the ALSA test
> > files and configuration that have whitespace in both some .conf and even
> > some symbolic links.
> > 
> > Example error:
> 
> The error messages don't really add any value here.
> <snip>
> 

It was really to give output of what happen when file with whitespace are used.
The shell is not so chatty with this so these error are really just the mode gid
and other values that gets parsed with the filename whitespace.

> > To correctly handle this problem, rework the gen_initramfs.sh and
> > gen_init_cpio.c to guard all the path with "" to handle all kind of
> > whitespace for filename/path.
> > 
> > The default_cpio_list is also updated to follow this new pattern.
> > 
> > Signed-off-by: Christian Marangi <ansuelsmth@...il.com>
> > ---
> >  usr/default_cpio_list |  6 +++---
> >  usr/gen_init_cpio.c   | 10 +++++-----
> >  usr/gen_initramfs.sh  | 27 +++++++++++++++++++--------
> >  3 files changed, 27 insertions(+), 16 deletions(-)
> > 
> > diff --git a/usr/default_cpio_list b/usr/default_cpio_list
> > index 37b3864066e8..d4a66b4aa7f7 100644
> > --- a/usr/default_cpio_list
> > +++ b/usr/default_cpio_list
> > @@ -1,6 +1,6 @@
> >  # SPDX-License-Identifier: GPL-2.0-only
> >  # This is a very simple, default initramfs
> >  
> > -dir /dev 0755 0 0
> > -nod /dev/console 0600 0 0 c 5 1
> > -dir /root 0700 0 0
> > +dir "/dev" 0755 0 0
> > +nod "/dev/console" 0600 0 0 c 5 1
> > +dir "/root" 0700 0 0
> > diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
> > index b7296edc6626..ca5950998841 100644
> > --- a/usr/gen_init_cpio.c
> > +++ b/usr/gen_init_cpio.c
> > @@ -166,7 +166,7 @@ static int cpio_mkslink_line(const char *line)
> >  	int gid;
> >  	int rc = -1;
> >  
> > -	if (5 != sscanf(line, "%" str(PATH_MAX) "s %" str(PATH_MAX) "s %o %d %d", name, target, &mode, &uid, &gid)) {
> > +	if (5 != sscanf(line, "\"%" str(PATH_MAX) "[^\"]\" \"%" str(PATH_MAX) "[^\"]\" %o %d %d", name, target, &mode, &uid, &gid)) {
> 
> This breaks parsing of existing manifest files, so is unacceptable
> IMO. If we really want to go down the route of having gen_init_cpio
> support space-separated paths, then perhaps a new --field-separator
> parameter might make sense. For your specific workload it seems that
> simply using an external cpio archiver with space support (e.g. GNU
> cpio --null) would make sense. Did you consider going down that
> path?
> 

This is mostly why this is posted as RFC. I honestly wants to fix this in the
linux tool instead of using external tools.

So is there an actual use of manually passing the cpio list instead of
generating one with the script? (just asking not saying that there isn't one)

One case I have (the scenario here is OpenWrt) is when a base cpio_list is
provided and then stuff is appended to it.

In such case yes there is a problem since the format changed.

My solution to this would be introduce new type that will have the new pattern.
This way we can keep support for the old list and still handle whitespace files.

An idea might be to have the file type with capital letter to differenciate with
the old one.

Something like 

FILE "path" "location" ...
SLINK "name" "target" ...
NODE ...

What do you think?

The option of --field-separator might also work but it might complicate stuff in
the .c tool as a more ""manual"" tokenizer will be needed than the simple
implementation currently present.

I'm open to both solution. Lets just agree on one of the 2.

-- 
	Ansuel