Re: [PATCH 1/4] rootfs: introduce wrapper to run commands against a rootfs

["'cedric.hombourger@siemens.com' via isar-users" <isar-users@googlegroups.com>]

On Thu, 2025-05-22 at 14:32 +0000, Moessbauer, Felix (FT RPD CED OES-
DE) wrote:
> On Mon, 2025-05-19 at 13:57 +0200, Cedric Hombourger wrote:
> > "sudo chroot" is used in several places to run commands inside
> > rootfs
> > directories constructed by Isar. There are cases where a command
> > could
> > be used without elevated privileges as long as special folders such
> > as
> > /isar-apt are mounted (they are often referenced as /isar-apt in
> > configuration files found in the target rootfs). For such cases,
> > bubblewrap may be used to create a non-privileged namespace (either
> > in a bare/native environment or within a docker/podman container)
> > where the command will be executed as if chroot had been used. The
> > rootfs may also be the host root file-system: this should however
> > be used with care to avoid host contamination problems (note: Isar
> > already relies on a number of host tools).
> 
> Hi, this looks promising. I gave it a try on some of our internal
> layers (arm64) in a custom kas container under podman.
> 
> I'm wondering if this could also be used to run the apt in
> do_rootfs_install natively (maybe in combination with dpkg --root).
> 
> Tested-by: Felix Moessbauer <felix.moessbauer@siemens.com>

Dear maintainers, can we move forward with these changes or are there
any concerns that need to be addressed?

Thank you!

> 
> Felix
> 
> > 
> > Signed-off-by: Cedric Hombourger <cedric.hombourger@siemens.com>
> > ---
> >  RECIPE-API-CHANGELOG.md     |  6 ++++
> >  doc/user_manual.md          |  1 +
> >  meta/classes/rootfs.bbclass | 66
> > +++++++++++++++++++++++++++++++++++++
> >  3 files changed, 73 insertions(+)
> > 
> > diff --git a/RECIPE-API-CHANGELOG.md b/RECIPE-API-CHANGELOG.md
> > index a4cf1338..725737b2 100644
> > --- a/RECIPE-API-CHANGELOG.md
> > +++ b/RECIPE-API-CHANGELOG.md
> > @@ -722,3 +722,9 @@ Optional fields of the isar-apt repo can be
> > controlled by adding to the
> >  
> >  Changes in next
> >  ---------------
> > +
> > +### Require bubblewrap to run non-privileged commands with bind-
> > mounts
> > +
> > +Isar occasionally needs to run commands within root file-systems
> > that it
> > +builds and with several bind-mounts (e.g. /isar-apt). bubblewrap
> > may
> > be
> > +used in Isar classes instead of `sudo chroot`.
> > diff --git a/doc/user_manual.md b/doc/user_manual.md
> > index 0dc317c3..3cf1a9aa 100644
> > --- a/doc/user_manual.md
> > +++ b/doc/user_manual.md
> > @@ -75,6 +75,7 @@ Install the following packages:
> >  ```
> >  apt install \
> >    binfmt-support \
> > +  bubblewrap \
> >    bzip2 \
> >    mmdebstrap \
> >    arch-test \
> > diff --git a/meta/classes/rootfs.bbclass
> > b/meta/classes/rootfs.bbclass
> > index 5f877962..5b96b414 100644
> > --- a/meta/classes/rootfs.bbclass
> > +++ b/meta/classes/rootfs.bbclass
> > @@ -34,6 +34,72 @@ export LANG = "C"
> >  export LANGUAGE = "C"
> >  export LC_ALL = "C"
> >  
> > +# Execute a command against a rootfs and with isar-apt bind-
> > mounted.
> > +# Additional mounts may be specified using --bind <source>
> > <target>
> > and a
> > +# custom directory for the command to be executed with --chdir
> > <dir>. The
> > +# command is assumed to follow the special "--" argument. This
> > would
> > replace
> > +# "sudo chroot" calls especially when a native command may be used
> > instead of
> > +# chroot'ed command and without elevated privileges (the command
> > will likely
> > +# take the rootfs as argument; e.g. apt-get -o Dir=${ROOTFSDIR}).
> > If
> > the
> > +# optional rootfs argument is omitted, the host rootfs will be
> > used
> > (e.g. to
> > +# run native commands): this should be used with care.
> > +#
> > +# Usage: rootfs_cmd [options] [rootfs] -- command
> > +#
> > +rootfs_cmd() {
> > +    set -- "$@"
> > +    bwrap_args="--bind ${REPO_ISAR_DIR}/${DISTRO} /isar-apt"
> > +    rootfs=""
> > +
> > +    while [ "${#}" -gt "0" ] && [ "${1}" != "--" ]; do
> > +        case "${1}" in
> > +            --bind)
> > +                if [ "${#}" -lt "3" ]; then
> > +                    bbfatal "--bind requires two arguments"
> > +                fi
> > +                bwrap_args="${bwrap_args} --bind ${2} ${3}"
> > +                shift 3
> > +                ;;
> > +            --chdir)
> > +                if [ "${#}" -lt "2" ]; then
> > +                    bbfatal "${1} requires an argument"
> > +                fi
> > +                bwrap_args="${bwrap_args} ${1} ${2}"
> > +                shift 2
> > +                ;;
> > +            -*)
> > +                bbfatal "${1} is not a supported option!"
> > +                ;;
> > +            *)
> > +                if [ -z "${rootfs}" ]; then
> > +                    rootfs="${1}"
> > +                    shift
> > +                else
> > +                    bbfatal "unexpected argument '${1}'"
> > +                fi
> > +                ;;
> > +        esac
> > +    done
> > +
> > +    if [ -n "${rootfs}" ]; then
> > +        bwrap_args="${bwrap_args} --bind ${rootfs} ${rootfs}"
> > +    fi
> > +
> > +    if [ "${#}" -le "1" ] || [ "${1}" != "--" ]; then
> > +        bbfatal "no command specified (missing --)"
> > +    fi
> > +    shift  # remove "--", command and its arguments follows
> > +
> > +    for ro_d in bin etc lib lib64 sys usr var; do
> > +        [ -d ${rootfs}/${ro_d} ] || continue
> > +        bwrap_args="${bwrap_args} --ro-bind ${rootfs}/${ro_d}
> > /${ro_d}"
> > +    done
> > +
> > +    bwrap --unshare-user --unshare-pid ${bwrap_args} \
> > +        --dev-bind /dev /dev --proc /proc --tmpfs /tmp \
> > +        -- "${@}"
> > +}
> > +
> >  rootfs_do_mounts[weight] = "3"
> >  rootfs_do_mounts() {
> >      sudo -s <<'EOSUDO'
> 

-- 
Cedric Hombourger
Siemens AG
www.siemens.com

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