Re: [PATCH v6 01/10] wic: Fix permissions when using exclude or include path

["Paul Barker" <pbarker@konsulko.com>]

On Tue, 14 Apr 2020 15:36:05 +0200
Ricardo Ribalda Delgado <ricardo@ribalda.com> wrote:

> When parameters include_path or exclude_path are passed to the rootfs
> plugin, it will copy the partition content into a folder and make all
> the modifications there.
> 
> This is done using copyhardlinktree(), which does not take into
> consideration the content of the pseudo folder, which contains the
> information about the right permissions and ownership of the folders.
> 
> This results in a rootfs owned by the user that is running the wic
> command (usually UID 1000), which makes some rootfs unbootable.
> 
> This bug can be easily triggerd with the following .wks
> 
> part / --source rootfs --fstype=ext4 --exclude-path=home
> 
> And this sequence:
> 
> $ wic create test-permissions -e core-image-minimal -o test/
> $ sudo mount test/test-permissions-202004080823-sda.direct.p1 /mnt
> $ ls -la /mnt/etc/shadow
> 
> To fix this we copy the content of the pseudo folders to the new folder
> and modify the pseudo database using the "pseudo -B" command.
> 
> If the rootfs is not a rootfs generated by bitbake a warning is shown
> making the user aware that the permissions on the target might not match
> what he expects.
> 
> WARNING: /tmp/test/../pseudo folder does not exist. Usernames and permissions will be invalid
> 
> Cc: Paul Barker <pbarker@konsulko.com>
> Signed-off-by: Ricardo Ribalda Delgado <ricardo@ribalda.com>
> ---
>  scripts/lib/wic/partition.py             |  7 +++--
>  scripts/lib/wic/plugins/source/rootfs.py | 36 ++++++++++++++++++++++--
>  2 files changed, 37 insertions(+), 6 deletions(-)
> 
> diff --git a/scripts/lib/wic/partition.py b/scripts/lib/wic/partition.py
> index 2d95f78439..b02711be37 100644
> --- a/scripts/lib/wic/partition.py
> +++ b/scripts/lib/wic/partition.py
> @@ -190,7 +190,7 @@ class Partition():
>                             (self.mountpoint, self.size, self.fixed_size))
>  
>      def prepare_rootfs(self, cr_workdir, oe_builddir, rootfs_dir,
> -                       native_sysroot, real_rootfs = True):
> +                       native_sysroot, real_rootfs = True, pseudo_dir = None):
>          """
>          Prepare content for a rootfs partition i.e. create a partition
>          and fill it from a /rootfs dir.
> @@ -198,8 +198,9 @@ class Partition():
>          Currently handles ext2/3/4, btrfs, vfat and squashfs.
>          """
>          p_prefix = os.environ.get("PSEUDO_PREFIX", "%s/usr" % native_sysroot)
> -        p_localstatedir = os.environ.get("PSEUDO_LOCALSTATEDIR",
> -                                         "%s/../pseudo" %  rootfs_dir)
> +        if (pseudo_dir == None):
> +            pseudo_dir = "%s/../pseudo" %  rootfs_dir
> +        p_localstatedir = os.environ.get("PSEUDO_LOCALSTATEDIR", pseudo_dir)
>          p_passwd = os.environ.get("PSEUDO_PASSWD", rootfs_dir)
>          p_nosymlinkexp = os.environ.get("PSEUDO_NOSYMLINKEXP", "1")
>          pseudo = "export PSEUDO_PREFIX=%s;" % p_prefix
> diff --git a/scripts/lib/wic/plugins/source/rootfs.py b/scripts/lib/wic/plugins/source/rootfs.py
> index 705aeb5563..caad9efccc 100644
> --- a/scripts/lib/wic/plugins/source/rootfs.py
> +++ b/scripts/lib/wic/plugins/source/rootfs.py
> @@ -20,7 +20,7 @@ from oe.path import copyhardlinktree
>  
>  from wic import WicError
>  from wic.pluginbase import SourcePlugin
> -from wic.misc import get_bitbake_var
> +from wic.misc import get_bitbake_var, exec_native_cmd
>  
>  logger = logging.getLogger('wic')
>  
> @@ -44,6 +44,15 @@ class RootfsPlugin(SourcePlugin):
>  
>          return os.path.realpath(image_rootfs_dir)
>  
> +    @staticmethod
> +    def __get_pseudo(native_sysroot, rootfs, pseudo_dir):
> +        pseudo = "export PSEUDO_PREFIX=%s/usr;" % native_sysroot
> +        pseudo += "export PSEUDO_LOCALSTATEDIR=%s;" % pseudo_dir
> +        pseudo += "export PSEUDO_PASSWD=%s;" % rootfs
> +        pseudo += "export PSEUDO_NOSYMLINKEXP=1;"
> +        pseudo += "%s " % get_bitbake_var("FAKEROOTCMD")
> +        return pseudo
> +
>      @classmethod
>      def do_prepare_partition(cls, part, source_params, cr, cr_workdir,
>                               oe_builddir, bootimg_dir, kernel_dir,
> @@ -68,8 +77,14 @@ class RootfsPlugin(SourcePlugin):
>                                 "it is not a valid path, exiting" % part.rootfs_dir)
>  
>          part.rootfs_dir = cls.__get_rootfs_dir(rootfs_dir)
> +        pseudo_dir = os.path.join(part.rootfs_dir, "../pseudo")
> +        if not os.path.lexists(pseudo_dir):
> +            logger.warn("%s folder does not exist. "
> +                        "Usernames and permissions will be invalid " % pseudo_dir)
> +            pseudo_dir = None
>  
>          new_rootfs = None
> +        new_pseudo = None
>          # Handle excluded paths.
>          if part.exclude_path or part.include_path:
>              # We need a new rootfs directory we can delete files from. Copy to
> @@ -78,9 +93,23 @@ class RootfsPlugin(SourcePlugin):
>  
>              if os.path.lexists(new_rootfs):
>                  shutil.rmtree(os.path.join(new_rootfs))
> -
>              copyhardlinktree(part.rootfs_dir, new_rootfs)
>  
> +            # Convert the pseudo directory to its new location
> +            if (pseudo_dir):
> +                new_pseudo = os.path.join(new_rootfs, "../pseudo%d" % part.lineno)

I still don't like this, it's unclear from looking at the patch alone
that it's safe to step up the directory tree here.

As I've said before, let's use an explicit path instead, such as:

    new_pseudo = os.path.realpath(os.path.join(cr_workdir, "pseudo%d" % part.lineno))

Then there's no '..', it's obviously safe and it's less likely someone
will break things by accident in the future.

> +                if os.path.lexists(new_pseudo):
> +                    shutil.rmtree(new_pseudo)
> +                os.mkdir(new_pseudo)
> +                shutil.copy(os.path.join(pseudo_dir, "files.db"),
> +                            os.path.join(new_pseudo, "files.db"))
> +
> +                pseudo_cmd = "%s -B -m %s -M %s" % (cls.__get_pseudo(native_sysroot,
> +                                                                     new_rootfs,
> +                                                                     new_pseudo),
> +                                                    part.rootfs_dir, new_rootfs)
> +                exec_native_cmd(pseudo_cmd, native_sysroot)
> +
>              for path in part.include_path or []:
>                  copyhardlinktree(path, new_rootfs)
>  
> @@ -112,4 +141,5 @@ class RootfsPlugin(SourcePlugin):
>                      shutil.rmtree(full_path)
>  
>          part.prepare_rootfs(cr_workdir, oe_builddir,
> -                            new_rootfs or part.rootfs_dir, native_sysroot)
> +                            new_rootfs or part.rootfs_dir, native_sysroot,
> +                            pseudo_dir = new_pseudo or pseudo_dir)

-- 
Paul Barker
Konsulko Group