linux-kernel - Re: [PATCH 1/1] squashfs: enable idmapped mounts

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Message-ID: <20221025074637.v6c243giy7itbimp@wittgenstein>
Date:   Tue, 25 Oct 2022 09:46:37 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Michael Weiß <michael.weiss@...ec.fraunhofer.de>
Cc:     Phillip Lougher <phillip@...ashfs.org.uk>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Seth Forshee <sforshee@...nel.org>
Subject: Re: [PATCH 1/1] squashfs: enable idmapped mounts

On Mon, Oct 24, 2022 at 09:15:52PM +0200, Michael Weiß wrote:
> For squashfs all needed functionality for idmapped mounts is already
> implemented by the generic handlers in the VFS. Thus, it is sufficient
> to just enable the corresponding FS_ALLOW_IDMAP flag to support
> idmapped mounts.
> 
> We use this for unprivileged (user namespaced) containers based on
> squashfs images as rootfs in GyroidOS.
> 
> A simple test using the mount-idmapped tool executed as user with
> uid=1000 looks as follows:
> 
> $ mkdir test
> $ echo "test" > test/test_file
> $ mksquashfs test/ fs.img
> $ sudo mkdir /mnt/test
> $ sudo mkdir /mnt/mapped
> $ sudo mount fs.img -o loop /mnt/test/
> $ sudo ./mount-idmapped --map-mount b:1000:2000:1 /mnt/test/ /mnt/mapped/
> 
> $ mount | tail -n2
> fs.img on /mnt/test type squashfs (ro,relatime,errors=continue)
> fs.img on /mnt/mapped type squashfs (ro,relatime,idmapped,errors=continue)
> 
> $ ls -lan /mnt/test/
> total 5
> drwxr-xr-x 2 1000 1000   32 Okt 24 13:36 .
> drwxr-xr-x 6    0    0 4096 Okt 24 13:38 ..
> -rw-r--r-- 1 1000 1000    5 Okt 24 13:36 test_file
> 
> $ ls -lan /mnt/mapped/
> total 5
> drwxr-xr-x 2 2000 2000   32 Okt 24 13:36 .
> drwxr-xr-x 6    0    0 4096 Okt 24 13:38 ..
> -rw-r--r-- 1 2000 2000    5 Okt 24 13:36 test_file
> 
> Signed-off-by: Michael Weiß <michael.weiss@...ec.fraunhofer.de>
> ---

This should indeed be all that is needed. Looks good to me,
Reviewed-by: Christian Brauner <brauner@...nel.org>