2019-11-10 18:35:28

by Nicolas Iooss

[permalink] [raw]
Subject: Intent to add support for cryfs

Hello,
I am using CryFS (https://www.cryfs.org/) in order to encrypt some
files in a shared directory. Before writing a policy for this software
and upstreaming it to refpolicy, I am wondering how this should be
handled.

CryFS is a software that can be run by non-root users that have access
to /dev/fuse. Its command is directly used to mount a directory
("/usr/bin/cryfs basedir mountpoint"), like command "mount".
Unmounting a mountpoint is done with "fusermount -u mountpoint",
/usr/bin/fusermount being a setuid-root program labeled mount_exec_t.
Currently, sysadm_t cannot use CryFS because it is not allowed to open
and use /dev/fuse (ie. fuse_device_t). Moreover labeling CryFS as
mount_exec_t makes mount_t require more accesses (reading a
configuration file from the base directory, reading
/proc/sys/crypto/fips_enabled, using pipes, etc.).

Therefore I am thinking of creating a new policy module for cryfs,
which could be shared with other similar software like EncFS
(https://vgough.github.io/encfs/). Does this sound like something
acceptable? Did I miss an existing module that can be extended in
order to support CryFS?

Thanks,
Nicolas


2019-11-12 10:31:01

by Dominick Grift

[permalink] [raw]
Subject: Re: Intent to add support for cryfs

On Sun, Nov 10, 2019 at 07:32:43PM +0100, Nicolas Iooss wrote:
> Hello,
> I am using CryFS (https://www.cryfs.org/) in order to encrypt some
> files in a shared directory. Before writing a policy for this software
> and upstreaming it to refpolicy, I am wondering how this should be
> handled.

Sounds somewhat like gocryptfs.
This is how i implemented policy for that:
https://defensec.nl/gitweb/dssp2.git/blob/HEAD:/policy/applications/g/gocryptfs.cil


>
> CryFS is a software that can be run by non-root users that have access
> to /dev/fuse. Its command is directly used to mount a directory
> ("/usr/bin/cryfs basedir mountpoint"), like command "mount".
> Unmounting a mountpoint is done with "fusermount -u mountpoint",
> /usr/bin/fusermount being a setuid-root program labeled mount_exec_t.
> Currently, sysadm_t cannot use CryFS because it is not allowed to open
> and use /dev/fuse (ie. fuse_device_t). Moreover labeling CryFS as
> mount_exec_t makes mount_t require more accesses (reading a
> configuration file from the base directory, reading
> /proc/sys/crypto/fips_enabled, using pipes, etc.).
>
> Therefore I am thinking of creating a new policy module for cryfs,
> which could be shared with other similar software like EncFS
> (https://vgough.github.io/encfs/). Does this sound like something
> acceptable? Did I miss an existing module that can be extended in
> order to support CryFS?
>
> Thanks,
> Nicolas
>

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Dominick Grift


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