linux-kernel - [PATCH] security/lsm_hooks: Updated set/remove xattr documentation

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Message-Id: <20190710190607.5026-1-carmeli.tamir@gmail.com>
Date:   Wed, 10 Jul 2019 15:06:07 -0400
From:   Carmeli Tamir <carmeli.tamir@...il.com>
To:     keescook@...omium.org, casey@...aufler-ca.com,
        james.morris@...rosoft.com, efremov@...ras.ru,
        viro@...iv.linux.org.uk, dhowells@...hat.com,
        linux-kernel@...r.kernel.org, carmeli.tamir@...il.com
Subject: [PATCH] security/lsm_hooks: Updated set/remove xattr documentation

The inode_setxattr and inode_removexattr hooks check for CAP_SYS_ADMIN
capability when no LSMs exist. When LSMs exist, the hook expects
them to check for capabilities - which SMACK and SELinux indeed do.

This behavior is only mentioned in a comment in the 
hooks' implementation. This patch makes it clearer for 
LSM programmers that when implememting these hooks they are
responsible for the CAP check.

Signed-off-by: Carmeli Tamir <carmeli.tamir@...il.com>
---
 include/linux/lsm_hooks.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 47f58cfb6a19..d16c88a31ea9 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -377,7 +377,8 @@
  *	Return 0 if permission is granted.
  * @inode_setxattr:
  *	Check permission before setting the extended attributes
- *	@value identified by @name for @dentry.
+ *	@value identified by @name for @dentry. Note that the hook
+ *	is responsible to check for capabilities.
  *	Return 0 if permission is granted.
  * @inode_post_setxattr:
  *	Update inode security field after successful setxattr operation.
@@ -392,7 +393,8 @@
  *	Return 0 if permission is granted.
  * @inode_removexattr:
  *	Check permission before removing the extended attribute
- *	identified by @name for @dentry.
+ *	identified by @name for @dentry. Note that the hook
+ *	is responsible to check for capabilities.
  *	Return 0 if permission is granted.
  * @inode_getsecurity:
  *	Retrieve a copy of the extended attribute representation of the
-- 
2.21.0