Subject: Re: [PATCH] Label /sys/kernel/ns_last_pid as
 sysctl_kernel_ns_last_pid_t
To:     Lukas Vrabec <lvrabec@redhat.com>,
        selinux-refpolicy@vger.kernel.org
References: <20190408161907.10322-1-lvrabec@redhat.com>
From:   Chris PeBenito <pebenito@ieee.org>
Message-ID: <42a81b2d-115e-4202-832d-190ae1da46e6@ieee.org>
Date:   Tue, 9 Apr 2019 07:54:44 -0400
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On 4/8/19 12:19 PM, Lukas Vrabec wrote:
> CRIU can influence the PID of the threads it wants to create.
> CRIU uses /proc/sys/kernel/ns_last_pidto tell the kernel which
> PID it wants for the next clone().
> So it has to write to that file. This feels like a problematic as
> it opens up the container writing to all sysctl_kernel_t.
> 
> Using new label container_t will just write to
> sysctl_kernel_ns_last_pid_t instad writing to more generic
> sysctl_kernel_t files.
> ---
>   policy/modules/kernel/kernel.if | 60 +++++++++++++++++++++++++++++++++
>   policy/modules/kernel/kernel.te |  7 ++++
>   2 files changed, 67 insertions(+)
> 
> diff --git a/policy/modules/kernel/kernel.if b/policy/modules/kernel/kernel.if
> index 1ad282aa..3f0a2dbe 100644
> --- a/policy/modules/kernel/kernel.if
> +++ b/policy/modules/kernel/kernel.if
> @@ -2150,6 +2150,66 @@ interface(`kernel_mounton_kernel_sysctl_files',`
>   	allow $1 sysctl_kernel_t:file { getattr mounton };
>   ')
>   
> +########################################
> +## <summary>
> +##	Read kernel ns lastpid sysctls.
> +## </summary>
> +## <param name="domain">
> +##	<summary>
> +##	Domain allowed access.
> +##	</summary>
> +## </param>
> +## <rolecap/>
> +#
> +interface(`kernel_read_kernel_ns_lastpid_sysctls',`
> +	gen_require(`
> +		type proc_t, sysctl_t, sysctl_kernel_ns_last_pid_t;
> +	')
> +
> +	read_files_pattern($1, { proc_t sysctl_t sysctl_kernel_ns_last_pid_t }, sysctl_kernel_ns_last_pid_t)
> +
> +	list_dirs_pattern($1, { proc_t sysctl_t }, sysctl_kernel_ns_last_pid_t)
> +')
> +
> +########################################
> +## <summary>
> +##	Do not audit attempts to write kernel ns lastpid sysctls.
> +## </summary>
> +## <param name="domain">
> +##	<summary>
> +##	Domain to not audit.
> +##	</summary>
> +## </param>
> +#
> +interface(`kernel_dontaudit_write_kernel_ns_lastpid_sysctl',`
> +	gen_require(`
> +		type sysctl_kernel_ns_last_pid_t;
> +	')
> +
> +	dontaudit $1 sysctl_kernel_ns_last_pid_t:file write;
> +')
> +
> +########################################
> +## <summary>
> +##	Read and write kernel ns lastpid sysctls.
> +## </summary>
> +## <param name="domain">
> +##	<summary>
> +##	Domain allowed access.
> +##	</summary>
> +## </param>
> +## <rolecap/>
> +#
> +interface(`kernel_rw_kernel_ns_lastpid_sysctl',`
> +	gen_require(`
> +		type proc_t, sysctl_t, sysctl_kernel_ns_last_pid_t;
> +	')
> +
> +	rw_files_pattern($1, { proc_t sysctl_t sysctl_kernel_ns_last_pid_t }, sysctl_kernel_ns_last_pid_t)
> +
> +	list_dirs_pattern($1, { proc_t sysctl_t }, sysctl_kernel_ns_last_pid_t)
> +')
> +
>   ########################################
>   ## <summary>
>   ##	Search filesystem sysctl directories.
> diff --git a/policy/modules/kernel/kernel.te b/policy/modules/kernel/kernel.te
> index 8e958074..f5ec1c22 100644
> --- a/policy/modules/kernel/kernel.te
> +++ b/policy/modules/kernel/kernel.te
> @@ -132,6 +132,11 @@ genfscon proc /sys/fs gen_context(system_u:object_r:sysctl_fs_t,s0)
>   type sysctl_kernel_t, sysctl_type;
>   genfscon proc /sys/kernel gen_context(system_u:object_r:sysctl_kernel_t,s0)
>   
> +# /sys/kernel/ns_last_pid file
> +type sysctl_kernel_ns_last_pid_t, sysctl_type;
> +fs_associate(sysctl_kernel_ns_last_pid_t)

Is this associate really necessary?  It's not used for any other sysctls.

> +genfscon proc /sys/kernel/ns_last_pid gen_context(system_u:object_r:sysctl_kernel_ns_last_pid_t,s0)
> +
>   # /proc/sys/kernel/modprobe file
>   type sysctl_modprobe_t, sysctl_type;
>   genfscon proc /sys/kernel/modprobe gen_context(system_u:object_r:sysctl_modprobe_t,s0)
> @@ -232,6 +237,8 @@ allow kernel_t sysctl_kernel_t:dir list_dir_perms;
>   allow kernel_t sysctl_kernel_t:file read_file_perms;
>   allow kernel_t sysctl_t:dir list_dir_perms;
>   
> +allow kernel_t sysctl_kernel_ns_last_pid_t:file read_file_perms;
> +
>   # Other possible mount points for the root fs are in files
>   allow kernel_t unlabeled_t:dir mounton;
>   # Kernel-generated traffic e.g., TCP resets on
> 


-- 
Chris PeBenito