Linux-Fsdevel Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Adrian Reber <areber@redhat.com>
To: "Christian Brauner" <christian.brauner@ubuntu.com>,
	"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>
Cc: Mike Rapoport <rppt@linux.ibm.com>,
	Radostin Stoyanov <rstoyanov1@gmail.com>,
	Adrian Reber <areber@redhat.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: [PATCH v6 1/7] capabilities: Introduce CAP_CHECKPOINT_RESTORE
Date: Sun, 19 Jul 2020 12:04:11 +0200	[thread overview]
Message-ID: <20200719100418.2112740-2-areber@redhat.com> (raw)
In-Reply-To: <20200719100418.2112740-1-areber@redhat.com>

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>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Reviewed-by: Serge Hallyn <serge@hallyn.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:[~2020-07-19 10:05 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-19 10:04 [PATCH v6 0/7] " Adrian Reber
2020-07-19 10:04 ` Adrian Reber [this message]
2020-07-19 10:04 ` [PATCH v6 2/7] pid: use checkpoint_restore_ns_capable() for set_tid Adrian Reber
2020-07-19 10:04 ` [PATCH v6 3/7] pid_namespace: use checkpoint_restore_ns_capable() for ns_last_pid Adrian Reber
2020-07-19 10:04 ` [PATCH v6 4/7] proc: allow access in init userns for map_files with CAP_CHECKPOINT_RESTORE Adrian Reber
2020-07-19 16:50   ` Serge E. Hallyn
2020-07-19 10:04 ` [PATCH v6 5/7] prctl: Allow local CAP_CHECKPOINT_RESTORE to change /proc/self/exe Adrian Reber
2020-07-19 10:04 ` [PATCH v6 6/7] prctl: exe link permission error changed from -EINVAL to -EPERM Adrian Reber
2020-07-19 17:05   ` Serge E. Hallyn
2020-07-19 10:04 ` [PATCH v6 7/7] selftests: add clone3() CAP_CHECKPOINT_RESTORE test Adrian Reber
2020-07-19 18:17 ` [PATCH v6 0/7] capabilities: Introduce CAP_CHECKPOINT_RESTORE Christian Brauner
2020-07-20 11:54   ` Christian Brauner
2020-07-20 12:46     ` Adrian Reber
2020-07-20 12:58       ` Christian Brauner

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200719100418.2112740-2-areber@redhat.com \
    --to=areber@redhat.com \
    --cc=0x7f454c46@gmail.com \
    --cc=Nicolas.Viennot@twosigma.com \
    --cc=arnd@arndb.de \
    --cc=avagin@gmail.com \
    --cc=casey@schaufler-ca.com \
    --cc=chf@redhat.com \
    --cc=christian.brauner@ubuntu.com \
    --cc=dipeit@gmail.com \
    --cc=ebiederm@xmission.com \
    --cc=eparis@parisplace.org \
    --cc=gorcunov@openvz.org \
    --cc=jannh@google.com \
    --cc=kyurtsever@google.com \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-security-module@vger.kernel.org \
    --cc=mclapinski@google.com \
    --cc=oleg@redhat.com \
    --cc=ovzxemul@gmail.com \
    --cc=rppt@linux.ibm.com \
    --cc=rstoyanov1@gmail.com \
    --cc=sargun@sargun.me \
    --cc=selinux@vger.kernel.org \
    --cc=serge@hallyn.com \
    --cc=stephen.smalley.work@gmail.com \
    --subject='Re: [PATCH v6 1/7] capabilities: Introduce CAP_CHECKPOINT_RESTORE' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).