[refpolicy] Which labelling for namespace filesystem?

[dac.override@gmail.com (Dominick Grift)]

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On Wed, Jan 06, 2016 at 07:37:10PM +0100, Nicolas Iooss wrote:
> Hello,
> 
> On the system I'm using to get refpolicy working with Arch Linux, I have
> these lines in audit.log:
> 
>   type=AVC msg=audit(1451041210.334:794): avc:  denied  { read } for
>   pid=28829 comm="(ostnamed)" dev="nsfs" ino=4026532544
>   scontext=system_u:system_r:init_t
>   tcontext=system_u:object_r:unlabeled_t tclass=file permissive=1
> 
>   type=AVC msg=audit(1451041210.334:794): avc:  denied  { open } for
>   pid=28829 comm="(ostnamed)" path="net:[4026532544]" dev="nsfs"
>   ino=4026532544 scontext=system_u:system_r:init_t
>   tcontext=system_u:object_r:unlabeled_t tclass=file permissive=1
> 
> These accesses are caused by open("/proc/self/ns/net"...) in systemd
> setup_netns() function [1].  Indeed /proc/PID/ns/* symlinks target a
> special filesystem named nsfs which is used for setns() syscall [2].  As
> this filesystem is not defined in refpolicy, its files are currently
> unlabeled, which explains the audit records.
> 
> To fix this, I see two options:
> 
> * "fs_use_task nsfs gen_context(system_u:object_r:fs_t,s0);", so that
> programs already allowed to access the /proc/PID tree of a process can
> also open /proc/PID/ns/* files.
> 
> * "genfscon nsfs / gen_context(system_u:object_r:nsfs_t,s0))", with a
> new fs type.  Programs using setns() will then need to be granted
> opening and reading nsfs_t files, in addition to be allowed using
> /proc/PID/ files of the target process.

Have you tried this option? I recall having tried it, and not getting
this to work.

> 
> To my mind both options have benefits and drawbacks, and I am fine with
> both.  If it matters, I have not found anything related to nsfs in
> Fedora policy nor in Gentoo policy.  The only policy I have found using
> nsfs is https://github.com/doverride/cilpolicy/ and it uses the first
> option [4].
> 
> Which option should be considered for refpolicy?
> 
> Thanks,
> Nicolas
> 
> PS: if anyone wonders what is this init_t process with a pid which is
> not one and a weird comm field, it is actually the process which will
> become systemd-hostnamed.  Its comm got modified by
> rename_process_from_path() function [5].
> 
> [1] https://github.com/systemd/systemd/blob/v228/src/core/namespace.c#L682
> [2] http://man7.org/linux/man-pages/man2/setns.2.html
> [3]
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/fs/proc/namespaces.c?h=v4.3#n45
> [4]
> https://github.com/doverride/cilpolicy/blob/v0.1/sources/modules/base/fs/contexts.cil#L37
> [5]
> https://github.com/systemd/systemd/blob/v228/src/core/execute.c#L1003-L1032
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Dominick Grift
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