[ptxdist] Root filesystem creation regression

[ptxdist] Root filesystem creation regression

[Juergen Borleis]

Hi,

since commit 9c0ec1da583f32706372d2a6cefa9a05f77ee8d2
  "ptxd_lib_check_dir_permissions: also check parents for directories"

the "install_tree" macro may create directories which makes this test fail and 
I'm unable to create root filesystems anymore.

The problem pops up if "install_tree" tries to install a file to a directory 
which has different permissions than the usual ones (0775, root:root).

For example: "systemd" sets up the "/usr/share/dbus-1/system-services" with 
permissions 0755. If my own package tries to add another file to this directory 
the corresponding "install" tool in the install stage creates the whole path 
with standard 0755 permissions - because the "filesystem" in the package 
directory (e.g. platform-<name>/packages/<package>) is always empty. In a 
regular root filesystem it works, because the directory structure already 
exists (with the intended permissions), and the "install" tool has to copy the 
file only.

Using "install_tree" in my package in this case creates a conflict for 
the "system-services" directory (0755 versus 0775). I guess it will fail at 
more locations than only "install_tree", if someone adds more and more accurate 
permissions due to security reasons.

jb

-- 
Pengutronix e.K.                       | Juergen Borleis             |
Steuerwalder Str. 21                   | https://www.pengutronix.de/ |
31137 Hildesheim, Germany              | Phone: +49-5121-206917-128  |
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Re: [ptxdist] Root filesystem creation regression

[Michael Olbrich]

On Mon, Jun 22, 2020 at 09:55:51AM +0200, Juergen Borleis wrote:
> since commit 9c0ec1da583f32706372d2a6cefa9a05f77ee8d2
>   "ptxd_lib_check_dir_permissions: also check parents for directories"
> 
> the "install_tree" macro may create directories which makes this test fail and 
> I'm unable to create root filesystems anymore.
> 
> The problem pops up if "install_tree" tries to install a file to a directory 
> which has different permissions than the usual ones (0775, root:root).
> 
> For example: "systemd" sets up the "/usr/share/dbus-1/system-services" with 
> permissions 0755. If my own package tries to add another file to this directory 
> the corresponding "install" tool in the install stage creates the whole path 
> with standard 0755 permissions - because the "filesystem" in the package 
> directory (e.g. platform-<name>/packages/<package>) is always empty. In a 
> regular root filesystem it works, because the directory structure already 
> exists (with the intended permissions), and the "install" tool has to copy the 
> file only.
> 
> Using "install_tree" in my package in this case creates a conflict for 
> the "system-services" directory (0755 versus 0775). I guess it will fail at 
> more locations than only "install_tree", if someone adds more and more accurate 
> permissions due to security reasons.

So the error you got was that systemd tries to create system-services with
0755 and your package tries to create it with 0775, right?
This is no longer supported. All packages must create the same directories
with the same permissions.

The problem is that, in general, when two ipkgs contain the same directory
with different permissions then the result was non-deterministic. Either
permission could end up in the rootfs. For rootfs images we 'fixed' this by
applying all permissions again. However, that is only deterministic if only
on package provides explicit permissions for the directory. And that was
not checked.
And even that case is not without problems: This only works, wenn ptxdist
created rootfs images. It does not work when ipkgs are used in any other
way. And if the package that provides the permissions is disabled, then the
permissions change for the remaining system. That is not something that
should happen.

So if a directory has non standard permissions, then all packages that
install into this directory must created the directory first, with the
correct permissions.
FYI, this was broken in the last ptxdist release, but it should be fixed in
master.

'install_tree' is a bit of a special case here. The problem ist, that it
cannot know, which directories are implicit. So it will always create all
subdirectories (except the root directory of the tree). So you need to fix
the permission in the install stage.

Michael

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

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Re: [ptxdist] Root filesystem creation regression

[Juergen Borleis]

Hi Michael,

Michael Olbrich wrote:
> […]
> 'install_tree' is a bit of a special case here. The problem ist, that it
> cannot know, which directories are implicit. So it will always create all
> subdirectories (except the root directory of the tree). So you need to fix
> the permission in the install stage.

I do not want and I do not need to know how "systemd" likes its directories. I 
just want to *add* a file to this directory. And this is how it works if you 
run "make install" in your package for a regular root filesystem: The "install" 
tool just copies a file to this dedicated directory and uses the already 
existing directory (and its permissions) as-is - and everything is fine.
The conflict only happens in PTXdist due to all install stages always install 
into an "empty" filesystem.

jb

-- 
Pengutronix e.K.                       | Juergen Borleis             |
Steuerwalder Str. 21                   | https://www.pengutronix.de/ |
31137 Hildesheim, Germany              | Phone: +49-5121-206917-128  |
Amtsgericht Hildesheim, HRA 2686       | Fax:   +49-5121-206917-9    |

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Re: [ptxdist] Root filesystem creation regression

[Michael Olbrich]

On Mon, Jun 22, 2020 at 11:14:30AM +0200, Juergen Borleis wrote:
> Michael Olbrich wrote:
> > […]
> > 'install_tree' is a bit of a special case here. The problem ist, that it
> > cannot know, which directories are implicit. So it will always create all
> > subdirectories (except the root directory of the tree). So you need to fix
> > the permission in the install stage.
> 
> I do not want and I do not need to know how "systemd" likes its directories. I 
> just want to *add* a file to this directory. And this is how it works if you 
> run "make install" in your package for a regular root filesystem: The "install" 
> tool just copies a file to this dedicated directory and uses the already 
> existing directory (and its permissions) as-is - and everything is fine.
> The conflict only happens in PTXdist due to all install stages always install 
> into an "empty" filesystem.

No, the conflict happens because you don't tell ptxdist what you want. Your
directory has special permissions and ptxdist should not ignore that.
If you don't care about the directory permissions, then don't use
install_tree. Install the individual files with install_copy.

In general, 'just add a file to a directory' is not possible. There is no
way to tell opkg if the permissions of a directory are important or not.

The only way to _always_ get the correct permissions is to use 0755 when we
don't care and explicitly handle anything else in _all_ packages that touch
the relevant paths.

Michael

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

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