linux-kernel - [PATCH 1/2] capability: Introduce CAP_BLOCK

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Date:   Thu, 11 May 2023 15:05:19 +0800
From:   Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
To:     Serge Hallyn <serge@...lyn.com>, Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Frederick Lawler <fred@...udflare.com>,
        Jens Axboe <axboe@...nel.dk>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
Subject: [PATCH 1/2] capability: Introduce CAP_BLOCK_ADMIN

Separated fine-grained capability CAP_BLOCK_ADMIN from CAP_SYS_ADMIN.
For backward compatibility, the CAP_BLOCK_ADMIN capability is included
within CAP_SYS_ADMIN.

Some database products rely on shared storage to complete the
write-once-read-multiple and write-multiple-read-multiple functions.
When HA occurs, they rely on the PR (Persistent Reservations) protocol
provided by the storage layer to manage block device permissions to
ensure data correctness.

CAP_SYS_ADMIN is required in the PR protocol implementation of existing
block devices in the Linux kernel, which has too many sensitive
permissions, which may lead to risks such as container escape. The
kernel needs to provide more fine-grained permission management like
CAP_NET_ADMIN to avoid online products directly relying on root to run.

CAP_BLOCK_ADMIN can also provide support for other block device
operations that require CAP_SYS_ADMIN capabilities in the future,
ensuring that applications run with least privilege.

Signed-off-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
---
 include/linux/capability.h          | 5 +++++
 include/uapi/linux/capability.h     | 7 ++++++-
 security/selinux/include/classmap.h | 4 ++--
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/include/linux/capability.h b/include/linux/capability.h
index 0c356a517991..95b81a75806f 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -208,6 +208,11 @@ static inline bool checkpoint_restore_ns_capable(struct user_namespace *ns)
 		ns_capable(ns, CAP_SYS_ADMIN);
 }
 
+static inline bool block_admin_capable(void)
+{
+	return capable(CAP_BLOCK_ADMIN) || capable(CAP_SYS_ADMIN);
+}
+
 /* audit system wants to get cap info from files as well */
 int get_vfs_caps_from_disk(struct mnt_idmap *idmap,
 			   const struct dentry *dentry,
diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
index 3d61a0ae055d..7c07f5916289 100644
--- a/include/uapi/linux/capability.h
+++ b/include/uapi/linux/capability.h
@@ -417,7 +417,12 @@ struct vfs_ns_cap_data {
 
 #define CAP_CHECKPOINT_RESTORE	40
 
-#define CAP_LAST_CAP         CAP_CHECKPOINT_RESTORE
+/*
+ * Allow Persistent Reservations operations for block device
+ */
+#define CAP_BLOCK_ADMIN		41
+
+#define CAP_LAST_CAP		CAP_BLOCK_ADMIN
 
 #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 a3c380775d41..83eb32e3a5cd 100644
--- a/security/selinux/include/classmap.h
+++ b/security/selinux/include/classmap.h
@@ -28,9 +28,9 @@
 
 #define COMMON_CAP2_PERMS  "mac_override", "mac_admin", "syslog", \
 		"wake_alarm", "block_suspend", "audit_read", "perfmon", "bpf", \
-		"checkpoint_restore"
+		"checkpoint_restore", "block_admin"
 
-#if CAP_LAST_CAP > CAP_CHECKPOINT_RESTORE
+#if CAP_LAST_CAP > CAP_BLOCK_ADMIN
 #error New capability defined, please update COMMON_CAP2_PERMS.
 #endif
 
-- 
2.24.3 (Apple Git-128)