From patchwork Wed Jun 3 16:23:26 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Adrian Reber X-Patchwork-Id: 11585995 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 37FF4159A for ; Wed, 3 Jun 2020 16:24:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1A02320738 for ; Wed, 3 Jun 2020 16:24:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="SkytYYha" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726262AbgFCQYg (ORCPT ); Wed, 3 Jun 2020 12:24:36 -0400 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:32311 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726170AbgFCQYf (ORCPT ); Wed, 3 Jun 2020 12:24:35 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1591201472; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=l5wNWGAWcER1sXm4h1esAhVHOr4X55D6SxvEN9Yk3MA=; b=SkytYYha/7/0HkSfFOTG34FCO/Lj1mjwdwFapNqnJQ6QEBqrh0gNsTWEf0oJJwbVpTJ3L8 +yS+a8UVZDuTr/dJuuWGj+qnhSnpjN5Zs0pStNYSOHIUS7golBY7BV+vPA7TZq8+C192eX kyGdLYQd7qakQKOvs44iIspbEyPr3rk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-409-dynHbkedO62XE_42CvQ2hA-1; Wed, 03 Jun 2020 12:24:27 -0400 X-MC-Unique: dynHbkedO62XE_42CvQ2hA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8BBB7185696F; Wed, 3 Jun 2020 16:24:23 +0000 (UTC) Received: from dcbz.redhat.com (ovpn-113-67.ams2.redhat.com [10.36.113.67]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1BB7B19C71; Wed, 3 Jun 2020 16:24:18 +0000 (UTC) From: Adrian Reber To: Christian Brauner , Eric Biederman , Pavel Emelyanov , Oleg Nesterov , Dmitry Safonov <0x7f454c46@gmail.com>, Andrei Vagin , Nicolas Viennot , =?utf-8?b?TWljaGHFgiBDxYJh?= =?utf-8?b?cGnFhHNraQ==?= , Kamil Yurtsever , Dirk Petersen , Christine Flood , Casey Schaufler Cc: Mike Rapoport , Radostin Stoyanov , Adrian Reber , Cyrill Gorcunov , Serge Hallyn , Stephen Smalley , Sargun Dhillon , Arnd Bergmann , linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, selinux@vger.kernel.org, Eric Paris , Jann Horn , linux-fsdevel@vger.kernel.org Subject: [PATCH v2 1/3] capabilities: Introduce CAP_CHECKPOINT_RESTORE Date: Wed, 3 Jun 2020 18:23:26 +0200 Message-Id: <20200603162328.854164-2-areber@redhat.com> In-Reply-To: <20200603162328.854164-1-areber@redhat.com> References: <20200603162328.854164-1-areber@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org 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 Signed-off-by: Nicolas Viennot --- v2: - Renamed CAP_RESTORE to CAP_CHECKPOINT_RESTORE - Added a test - Added details about CRIU's use of map_files - Allow changing /proc/self/exe link with CAP_CHECKPOINT_RESTORE --- fs/proc/base.c | 8 ++++---- include/linux/capability.h | 6 ++++++ include/uapi/linux/capability.h | 9 ++++++++- kernel/pid.c | 2 +- kernel/pid_namespace.c | 2 +- security/selinux/include/classmap.h | 5 +++-- 6 files changed, 23 insertions(+), 9 deletions(-) diff --git a/fs/proc/base.c b/fs/proc/base.c index d86c0afc8a85..ce02f3a4b2d7 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -2189,16 +2189,16 @@ struct map_files_info { }; /* - * Only allow CAP_SYS_ADMIN to follow the links, due to concerns about how the - * symlinks may be used to bypass permissions on ancestor directories in the - * path to the file in question. + * Only allow CAP_SYS_ADMIN and CAP_CHECKPOINT_RESTORE to follow the links, due + * to concerns about how the symlinks may be used to bypass permissions on + * ancestor directories in the path to the file in question. */ static const char * proc_map_files_get_link(struct dentry *dentry, struct inode *inode, struct delayed_call *done) { - if (!capable(CAP_SYS_ADMIN)) + if (!(capable(CAP_SYS_ADMIN) || capable(CAP_CHECKPOINT_RESTORE))) return ERR_PTR(-EPERM); return proc_pid_get_link(dentry, inode, done); 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/kernel/pid.c b/kernel/pid.c index 3122043fe364..ada55c7b2b19 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -198,7 +198,7 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid, if (tid != 1 && !tmp->child_reaper) goto out_free; retval = -EPERM; - if (!ns_capable(tmp->user_ns, CAP_SYS_ADMIN)) + if (!checkpoint_restore_ns_capable(tmp->user_ns)) goto out_free; set_tid_size--; } diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c index 0e5ac162c3a8..ac135bd600eb 100644 --- a/kernel/pid_namespace.c +++ b/kernel/pid_namespace.c @@ -269,7 +269,7 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int write, struct ctl_table tmp = *table; int ret, next; - if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN)) + if (write && !checkpoint_restore_ns_capable(pid_ns->user_ns)) return -EPERM; /* diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h index 98e1513b608a..40cebde62856 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 From patchwork Wed Jun 3 16:23:27 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Adrian Reber X-Patchwork-Id: 11586001 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 5434E1667 for ; Wed, 3 Jun 2020 16:24:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3CA2820738 for ; Wed, 3 Jun 2020 16:24:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="aBxc2wFp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726266AbgFCQYi (ORCPT ); Wed, 3 Jun 2020 12:24:38 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:50771 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726243AbgFCQYg (ORCPT ); Wed, 3 Jun 2020 12:24:36 -0400 DKIM-Signature: v=1; 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Wed, 3 Jun 2020 16:24:29 +0000 (UTC) Received: from dcbz.redhat.com (ovpn-113-67.ams2.redhat.com [10.36.113.67]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9C98319C71; Wed, 3 Jun 2020 16:24:24 +0000 (UTC) From: Adrian Reber To: Christian Brauner , Eric Biederman , Pavel Emelyanov , Oleg Nesterov , Dmitry Safonov <0x7f454c46@gmail.com>, Andrei Vagin , Nicolas Viennot , =?utf-8?b?TWljaGHFgiBDxYJh?= =?utf-8?b?cGnFhHNraQ==?= , Kamil Yurtsever , Dirk Petersen , Christine Flood , Casey Schaufler Cc: Mike Rapoport , Radostin Stoyanov , Adrian Reber , Cyrill Gorcunov , Serge Hallyn , Stephen Smalley , Sargun Dhillon , Arnd Bergmann , linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, selinux@vger.kernel.org, Eric Paris , Jann Horn , linux-fsdevel@vger.kernel.org Subject: [PATCH v2 2/3] selftests: add clone3() CAP_CHECKPOINT_RESTORE test Date: Wed, 3 Jun 2020 18:23:27 +0200 Message-Id: <20200603162328.854164-3-areber@redhat.com> In-Reply-To: <20200603162328.854164-1-areber@redhat.com> References: <20200603162328.854164-1-areber@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org This adds a test that changes its UID, uses capabilities to get CAP_CHECKPOINT_RESTORE and uses clone3() with set_tid to create a process with a given PID as non-root. Signed-off-by: Adrian Reber --- tools/testing/selftests/clone3/Makefile | 4 +- .../clone3/clone3_cap_checkpoint_restore.c | 203 ++++++++++++++++++ 2 files changed, 206 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c diff --git a/tools/testing/selftests/clone3/Makefile b/tools/testing/selftests/clone3/Makefile index cf976c732906..ef7564cb7abe 100644 --- a/tools/testing/selftests/clone3/Makefile +++ b/tools/testing/selftests/clone3/Makefile @@ -1,6 +1,8 @@ # SPDX-License-Identifier: GPL-2.0 CFLAGS += -g -I../../../../usr/include/ +LDLIBS += -lcap -TEST_GEN_PROGS := clone3 clone3_clear_sighand clone3_set_tid +TEST_GEN_PROGS := clone3 clone3_clear_sighand clone3_set_tid \ + clone3_cap_checkpoint_restore include ../lib.mk diff --git a/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c b/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c new file mode 100644 index 000000000000..2cc3d57b91f2 --- /dev/null +++ b/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c @@ -0,0 +1,203 @@ +// SPDX-License-Identifier: GPL-2.0 + +/* + * Based on Christian Brauner's clone3() example. + * These tests are assuming to be running in the host's + * PID namespace. + */ + +/* capabilities related code based on selftests/bpf/test_verifier.c */ + +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "../kselftest.h" +#include "clone3_selftests.h" + +#ifndef MAX_PID_NS_LEVEL +#define MAX_PID_NS_LEVEL 32 +#endif + +static void child_exit(int ret) +{ + fflush(stdout); + fflush(stderr); + _exit(ret); +} + +static int call_clone3_set_tid(pid_t * set_tid, size_t set_tid_size) +{ + int status; + pid_t pid = -1; + + struct clone_args args = { + .exit_signal = SIGCHLD, + .set_tid = ptr_to_u64(set_tid), + .set_tid_size = set_tid_size, + }; + + pid = sys_clone3(&args, sizeof(struct clone_args)); + if (pid < 0) { + ksft_print_msg("%s - Failed to create new process\n", + strerror(errno)); + return -errno; + } + + if (pid == 0) { + int ret; + char tmp = 0; + + ksft_print_msg + ("I am the child, my PID is %d (expected %d)\n", + getpid(), set_tid[0]); + + if (set_tid[0] != getpid()) + child_exit(EXIT_FAILURE); + child_exit(EXIT_SUCCESS); + } + + ksft_print_msg("I am the parent (%d). My child's pid is %d\n", + getpid(), pid); + + if (waitpid(pid, &status, 0) < 0) { + ksft_print_msg("Child returned %s\n", strerror(errno)); + return -errno; + } + + if (!WIFEXITED(status)) + return -1; + + return WEXITSTATUS(status); +} + +static int test_clone3_set_tid(pid_t * set_tid, + size_t set_tid_size, int expected) +{ + int ret; + + ksft_print_msg("[%d] Trying clone3() with CLONE_SET_TID to %d\n", + getpid(), set_tid[0]); + ret = call_clone3_set_tid(set_tid, set_tid_size); + + ksft_print_msg + ("[%d] clone3() with CLONE_SET_TID %d says :%d - expected %d\n", + getpid(), set_tid[0], ret, expected); + if (ret != expected) { + ksft_test_result_fail + ("[%d] Result (%d) is different than expected (%d)\n", + getpid(), ret, expected); + return -1; + } + ksft_test_result_pass + ("[%d] Result (%d) matches expectation (%d)\n", getpid(), ret, + expected); + + return 0; +} + +struct libcap { + struct __user_cap_header_struct hdr; + struct __user_cap_data_struct data[2]; +}; + +static int set_capability() +{ + cap_value_t cap_values[] = { CAP_SETUID, CAP_SETGID }; + struct libcap *cap; + int ret = -1; + cap_t caps; + + caps = cap_get_proc(); + if (!caps) { + perror("cap_get_proc"); + return -1; + } + + /* Drop all capabilities */ + if (cap_clear(caps)) { + perror("cap_clear"); + goto out; + } + + cap_set_flag(caps, CAP_EFFECTIVE, 2, cap_values, CAP_SET); + cap_set_flag(caps, CAP_PERMITTED, 2, cap_values, CAP_SET); + + cap = (struct libcap *) caps; + + /* 40 -> CAP_CHECKPOINT_RESTORE */ + cap->data[1].effective |= 1 << (40 - 32); + cap->data[1].permitted |= 1 << (40 - 32); + + if (cap_set_proc(caps)) { + perror("cap_set_proc"); + goto out; + } + ret = 0; +out: + if (cap_free(caps)) + perror("cap_free"); + return ret; +} + +int main(int argc, char *argv[]) +{ + pid_t pid; + int status; + int ret = 0; + pid_t set_tid[1]; + uid_t uid = getuid(); + + ksft_print_header(); + test_clone3_supported(); + ksft_set_plan(2); + + if (uid != 0) { + ksft_cnt.ksft_xskip = ksft_plan; + ksft_print_msg("Skipping all tests as non-root\n"); + return ksft_exit_pass(); + } + + memset(&set_tid, 0, sizeof(set_tid)); + + /* Find the current active PID */ + pid = fork(); + if (pid == 0) { + ksft_print_msg("Child has PID %d\n", getpid()); + child_exit(EXIT_SUCCESS); + } + if (waitpid(pid, &status, 0) < 0) + ksft_exit_fail_msg("Waiting for child %d failed", pid); + + /* After the child has finished, its PID should be free. */ + set_tid[0] = pid; + + if (set_capability()) + ksft_test_result_fail + ("Could not set CAP_CHECKPOINT_RESTORE\n"); + prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0); + /* This would fail without CAP_CHECKPOINT_RESTORE */ + setgid(1000); + setuid(1000); + set_tid[0] = pid; + ret |= test_clone3_set_tid(set_tid, 1, -EPERM); + if (set_capability()) + ksft_test_result_fail + ("Could not set CAP_CHECKPOINT_RESTORE\n"); + /* This should work as we have CAP_CHECKPOINT_RESTORE as non-root */ + ret |= test_clone3_set_tid(set_tid, 1, 0); + + return !ret ? ksft_exit_pass() : ksft_exit_fail(); +} From patchwork Wed Jun 3 16:23:28 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Adrian Reber X-Patchwork-Id: 11586003 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id B9A5490 for ; Wed, 3 Jun 2020 16:24:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9EB6F20679 for ; Wed, 3 Jun 2020 16:24:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="C+Obht5P" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726311AbgFCQYr (ORCPT ); Wed, 3 Jun 2020 12:24:47 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:30195 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726296AbgFCQYq (ORCPT ); Wed, 3 Jun 2020 12:24:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1591201485; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=cXciDkK7OoMQ0gJnd5P/3MbteHCW4WYolIjWhTKn9Z0=; b=C+Obht5Pa4PNdV1LcaaYEADbY9ygnIEwkqoDENvrwMu7hvN2pC7SpsqYeGw/UNPJRcnGQh Czj/nGDhtsNckVeaYjMZ/UAhnq+yBDs1Zxu6uGZCcrzIh4zC+yy0AerMFcnysutGGzwvEn ajfEVX9N8ogmT+KlA9gtKG3DjkbrGhI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-272-RG2C8sGoMUe5_ujS4Peu8g-1; Wed, 03 Jun 2020 12:24:43 -0400 X-MC-Unique: RG2C8sGoMUe5_ujS4Peu8g-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 54702EC1A2; Wed, 3 Jun 2020 16:24:40 +0000 (UTC) Received: from dcbz.redhat.com (ovpn-113-67.ams2.redhat.com [10.36.113.67]) by smtp.corp.redhat.com (Postfix) with ESMTP id 96B6119C71; Wed, 3 Jun 2020 16:24:30 +0000 (UTC) From: Adrian Reber To: Christian Brauner , Eric Biederman , Pavel Emelyanov , Oleg Nesterov , Dmitry Safonov <0x7f454c46@gmail.com>, Andrei Vagin , Nicolas Viennot , =?utf-8?b?TWljaGHFgiBDxYJh?= =?utf-8?b?cGnFhHNraQ==?= , Kamil Yurtsever , Dirk Petersen , Christine Flood , Casey Schaufler Cc: Mike Rapoport , Radostin Stoyanov , Adrian Reber , Cyrill Gorcunov , Serge Hallyn , Stephen Smalley , Sargun Dhillon , Arnd Bergmann , linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, selinux@vger.kernel.org, Eric Paris , Jann Horn , linux-fsdevel@vger.kernel.org Subject: [PATCH v2 3/3] prctl: Allow ptrace capable processes to change exe_fd Date: Wed, 3 Jun 2020 18:23:28 +0200 Message-Id: <20200603162328.854164-4-areber@redhat.com> In-Reply-To: <20200603162328.854164-1-areber@redhat.com> References: <20200603162328.854164-1-areber@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Nicolas Viennot The current process is authorized to change its /proc/self/exe link via two policies: 1) The current user can do checkpoint/restore In other words is CAP_SYS_ADMIN or CAP_CHECKPOINT_RESTORE capable. 2) The current user can use ptrace. With access to ptrace facilities, a process can do the following: fork a child, execve() the target executable, and have the child use ptrace() to replace the memory content of the current process. This technique makes it possible to masquerade an arbitrary program as any executable, even setuid ones. This commit also changes the permission error code from -EINVAL to -EPERM for consistency with the rest of the prctl() syscall when checking capabilities. Signed-off-by: Nicolas Viennot Signed-off-by: Adrian Reber --- kernel/sys.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) diff --git a/kernel/sys.c b/kernel/sys.c index fd46865b46ba..2f34108e26e0 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1994,12 +1994,23 @@ static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data if (prctl_map.exe_fd != (u32)-1) { /* - * Make sure the caller has the rights to - * change /proc/pid/exe link: only local sys admin should - * be allowed to. + * The current process is authorized to change its + * /proc/self/exe link via two policies: + * 1) The current user can do checkpoint/restore + * In other words is CAP_SYS_ADMIN or + * CAP_CHECKPOINT_RESTORE capable. + * 2) The current user can use ptrace. + * + * With access to ptrace facilities, a process can do the + * following: fork a child, execve() the target executable, + * and have the child use ptrace() to replace the memory + * content of the current process. This technique makes it + * possible to masquerade an arbitrary program as the target + * executable, even if it is setuid. */ - if (!ns_capable(current_user_ns(), CAP_SYS_ADMIN)) - return -EINVAL; + if (!(checkpoint_restore_ns_capable(current_user_ns()) || + security_ptrace_access_check(current, PTRACE_MODE_ATTACH_REALCREDS))) + return -EPERM; error = prctl_set_mm_exe_file(mm, prctl_map.exe_fd); if (error)