mapping with --readonly option

mapping with --readonly option

[Fourhundred Thecat]

Hello,

if I use the --readonly option to create a mapping, and mount it as my
root partition, can the mapping later be changed during runtime to
read-write ?

Or, in other words, if mapping was created as readonly, can I be sure
that it cannot be remapped to read-write while being mounted as my root
filesystem?

Ofcourse mapping can be closed and opened again, but I am asking here
specifically for mapping that is mounted as root filesystem, which
cannot be unmounted at runtime (as far as I know)

I am interested whether I can use readonly mapping as sort of security
feature to enforce read-only filesystem?

thank you

Re: mapping with --readonly option

[Arno Wagner]

You probably should mount it as readonly instead. Because
that gets remounted in the typical boot-process as r/w
so it definitely is possible.

If you want protection against a malicious root, this is
probably not the way to go, I think.

Regards,
Arno


On Sat, Nov 05, 2022 at 11:15:12 CET, Fourhundred Thecat wrote:
> Hello,
> 
> if I use the --readonly option to create a mapping, and mount it as my
> root partition, can the mapping later be changed during runtime to
> read-write ?
> 
> Or, in other words, if mapping was created as readonly, can I be sure
> that it cannot be remapped to read-write while being mounted as my root
> filesystem?
> 
> Ofcourse mapping can be closed and opened again, but I am asking here
> specifically for mapping that is mounted as root filesystem, which
> cannot be unmounted at runtime (as far as I know)
> 
> I am interested whether I can use readonly mapping as sort of security
> feature to enforce read-only filesystem?
> 
> thank you

-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno@wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
----
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If it's in the news, don't worry about it.  The very definition of 
"news" is "something that hardly ever happens." -- Bruce Schneier

Re: mapping with --readonly option

[Christoph Anton Mitterer]

On Sun, 2022-11-06 at 23:15 +0100, Arno Wagner wrote:
> You probably should mount it as readonly instead.

A -o ro filesystem mount is not necessarily actually read-only, the fs
itself may still change its own contents... e.g. journal or log tree
replays.


Cheers,
Chris.