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From: Christian Brauner <christian.brauner@ubuntu.com>
To: Adrian Reber <areber@redhat.com>
Cc: "Eric Biederman" <ebiederm@xmission.com>,
	"Pavel Emelyanov" <ovzxemul@gmail.com>,
	"Oleg Nesterov" <oleg@redhat.com>,
	"Dmitry Safonov" <0x7f454c46@gmail.com>,
	"Andrei Vagin" <avagin@gmail.com>,
	"Nicolas Viennot" <Nicolas.Viennot@twosigma.com>,
	"Michał Cłapiński" <mclapinski@google.com>,
	"Kamil Yurtsever" <kyurtsever@google.com>,
	"Dirk Petersen" <dipeit@gmail.com>,
	"Christine Flood" <chf@redhat.com>,
	"Casey Schaufler" <casey@schaufler-ca.com>,
	"Mike Rapoport" <rppt@linux.ibm.com>,
	"Radostin Stoyanov" <rstoyanov1@gmail.com>,
	"Cyrill Gorcunov" <gorcunov@openvz.org>,
	"Serge Hallyn" <serge@hallyn.com>,
	"Stephen Smalley" <stephen.smalley.work@gmail.com>,
	"Sargun Dhillon" <sargun@sargun.me>,
	"Arnd Bergmann" <arnd@arndb.de>,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org, selinux@vger.kernel.org,
	"Eric Paris" <eparis@parisplace.org>,
	"Jann Horn" <jannh@google.com>,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v5 1/6] capabilities: Introduce CAP_CHECKPOINT_RESTORE
Date: Wed, 15 Jul 2020 17:06:47 +0200	[thread overview]
Message-ID: <20200715150647.a24nz2iqrel62sfg@wittgenstein> (raw)
In-Reply-To: <20200715144954.1387760-2-areber@redhat.com>

On Wed, Jul 15, 2020 at 04:49:49PM +0200, Adrian Reber wrote:
> This patch introduces CAP_CHECKPOINT_RESTORE, a new capability facilitating
> checkpoint/restore for non-root users.
> 
> Over the last years, The CRIU (Checkpoint/Restore In Userspace) team has been
> asked numerous times if it is possible to checkpoint/restore a process as
> non-root. The answer usually was: 'almost'.
> 
> The main blocker to restore a process as non-root was to control the PID of the
> restored process. This feature available via the clone3 system call, or via
> /proc/sys/kernel/ns_last_pid is unfortunately guarded by CAP_SYS_ADMIN.
> 
> In the past two years, requests for non-root checkpoint/restore have increased
> due to the following use cases:
> * Checkpoint/Restore in an HPC environment in combination with a resource
>   manager distributing jobs where users are always running as non-root.
>   There is a desire to provide a way to checkpoint and restore long running
>   jobs.
> * Container migration as non-root
> * We have been in contact with JVM developers who are integrating
>   CRIU into a Java VM to decrease the startup time. These checkpoint/restore
>   applications are not meant to be running with CAP_SYS_ADMIN.
> 
> We have seen the following workarounds:
> * Use a setuid wrapper around CRIU:
>   See https://github.com/FredHutch/slurm-examples/blob/master/checkpointer/lib/checkpointer/checkpointer-suid.c
> * Use a setuid helper that writes to ns_last_pid.
>   Unfortunately, this helper delegation technique is impossible to use with
>   clone3, and is thus prone to races.
>   See https://github.com/twosigma/set_ns_last_pid
> * Cycle through PIDs with fork() until the desired PID is reached:
>   This has been demonstrated to work with cycling rates of 100,000 PIDs/s
>   See https://github.com/twosigma/set_ns_last_pid
> * Patch out the CAP_SYS_ADMIN check from the kernel
> * Run the desired application in a new user and PID namespace to provide
>   a local CAP_SYS_ADMIN for controlling PIDs. This technique has limited use in
>   typical container environments (e.g., Kubernetes) as /proc is
>   typically protected with read-only layers (e.g., /proc/sys) for hardening
>   purposes. Read-only layers prevent additional /proc mounts (due to proc's
>   SB_I_USERNS_VISIBLE property), making the use of new PID namespaces limited as
>   certain applications need access to /proc matching their PID namespace.
> 
> The introduced capability allows to:
> * Control PIDs when the current user is CAP_CHECKPOINT_RESTORE capable
>   for the corresponding PID namespace via ns_last_pid/clone3.
> * Open files in /proc/pid/map_files when the current user is
>   CAP_CHECKPOINT_RESTORE capable in the root namespace, useful for recovering
>   files that are unreachable via the file system such as deleted files, or memfd
>   files.
> 
> See corresponding selftest for an example with clone3().
> 
> Signed-off-by: Adrian Reber <areber@redhat.com>
> Signed-off-by: Nicolas Viennot <Nicolas.Viennot@twosigma.com>
> ---

Thanks!
This looks good now.
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>

>  include/linux/capability.h          | 6 ++++++
>  include/uapi/linux/capability.h     | 9 ++++++++-
>  security/selinux/include/classmap.h | 5 +++--
>  3 files changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/capability.h b/include/linux/capability.h
> index b4345b38a6be..1e7fe311cabe 100644
> --- a/include/linux/capability.h
> +++ b/include/linux/capability.h
> @@ -261,6 +261,12 @@ static inline bool bpf_capable(void)
>  	return capable(CAP_BPF) || capable(CAP_SYS_ADMIN);
>  }
>  
> +static inline bool checkpoint_restore_ns_capable(struct user_namespace *ns)
> +{
> +	return ns_capable(ns, CAP_CHECKPOINT_RESTORE) ||
> +		ns_capable(ns, CAP_SYS_ADMIN);
> +}
> +
>  /* audit system wants to get cap info from files as well */
>  extern int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps);
>  
> diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
> index 48ff0757ae5e..395dd0df8d08 100644
> --- a/include/uapi/linux/capability.h
> +++ b/include/uapi/linux/capability.h
> @@ -408,7 +408,14 @@ struct vfs_ns_cap_data {
>   */
>  #define CAP_BPF			39
>  
> -#define CAP_LAST_CAP         CAP_BPF
> +
> +/* Allow checkpoint/restore related operations */
> +/* Allow PID selection during clone3() */
> +/* Allow writing to ns_last_pid */
> +
> +#define CAP_CHECKPOINT_RESTORE	40
> +
> +#define CAP_LAST_CAP         CAP_CHECKPOINT_RESTORE
>  
>  #define cap_valid(x) ((x) >= 0 && (x) <= CAP_LAST_CAP)
>  
> diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
> index e54d62d529f1..ba2e01a6955c 100644
> --- a/security/selinux/include/classmap.h
> +++ b/security/selinux/include/classmap.h
> @@ -27,9 +27,10 @@
>  	    "audit_control", "setfcap"
>  
>  #define COMMON_CAP2_PERMS  "mac_override", "mac_admin", "syslog", \
> -		"wake_alarm", "block_suspend", "audit_read", "perfmon", "bpf"
> +		"wake_alarm", "block_suspend", "audit_read", "perfmon", "bpf", \
> +		"checkpoint_restore"
>  
> -#if CAP_LAST_CAP > CAP_BPF
> +#if CAP_LAST_CAP > CAP_CHECKPOINT_RESTORE
>  #error New capability defined, please update COMMON_CAP2_PERMS.
>  #endif
>  
> -- 
> 2.26.2
> 

  reply	other threads:[~2020-07-15 15:07 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-15 14:49 [PATCH v5 0/6] " Adrian Reber
2020-07-15 14:49 ` [PATCH v5 1/6] " Adrian Reber
2020-07-15 15:06   ` Christian Brauner [this message]
2020-07-15 14:49 ` [PATCH v5 2/6] pid: use checkpoint_restore_ns_capable() for set_tid Adrian Reber
2020-07-15 15:08   ` Christian Brauner
2020-07-15 14:49 ` [PATCH v5 3/6] pid_namespace: use checkpoint_restore_ns_capable() for ns_last_pid Adrian Reber
2020-07-15 15:08   ` Christian Brauner
2020-07-15 14:49 ` [PATCH v5 4/6] proc: allow access in init userns for map_files with CAP_CHECKPOINT_RESTORE Adrian Reber
2020-07-15 21:17   ` Cyrill Gorcunov
2020-07-16  8:51   ` Christian Brauner
2020-07-15 14:49 ` [PATCH v5 5/6] prctl: Allow checkpoint/restore capable processes to change exe link Adrian Reber
2020-07-15 15:20   ` Christian Brauner
2020-07-15 15:49     ` Nicolas Viennot
2020-07-15 14:49 ` [PATCH v5 6/6] selftests: add clone3() CAP_CHECKPOINT_RESTORE test Adrian Reber
2020-07-15 15:24   ` Christian Brauner
2020-07-18  3:24 ` [PATCH v5 0/6] capabilities: Introduce CAP_CHECKPOINT_RESTORE Serge E. Hallyn
2020-07-18 17:47   ` Christian Brauner

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