[PATCH] LSM: Revive CONFIG_DEFAULT_SECURITY_* for "make oldconfig"

[Tetsuo Handa]

Commit 70b62c25665f636c ("LoadPin: Initialize as ordered LSM") removed
CONFIG_DEFAULT_SECURITY_{SELINUX,SMACK,TOMOYO,APPARMOR,DAC} from
security/Kconfig and changed CONFIG_LSM to provide a fixed ordering as a
default value. That commit expected that existing users (upgrading from
Linux 5.0 and earlier) will edit CONFIG_LSM value in accordance with
their CONFIG_DEFAULT_SECURITY_* choice in their old kernel configs. But
since users might forget to edit CONFIG_LSM value, this patch revives
the choice (only for providing the default value for CONFIG_LSM) in order
to make sure that CONFIG_LSM reflects CONFIG_DEFAULT_SECURITY_* from their
old kernel configs.

Reported-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
 security/Kconfig | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/security/Kconfig b/security/Kconfig
index 1d6463f..743e594 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -239,9 +239,43 @@ source "security/safesetid/Kconfig"
 
 source "security/integrity/Kconfig"
 
+choice
+	prompt "Default security module [superseded by 'Ordered list of enabled LSMs' below]"
+	default DEFAULT_SECURITY_SELINUX if SECURITY_SELINUX
+	default DEFAULT_SECURITY_SMACK if SECURITY_SMACK
+	default DEFAULT_SECURITY_TOMOYO if SECURITY_TOMOYO
+	default DEFAULT_SECURITY_APPARMOR if SECURITY_APPARMOR
+	default DEFAULT_SECURITY_DAC
+
+	help
+	  This choice is there only for converting CONFIG_DEFAULT_SECURITY in old
+	  kernel config to CONFIG_LSM in new kernel config. Don't change this choice
+	  unless you are creating a fresh kernel config, for this choice will be
+	  ignored after CONFIG_LSM is once defined.
+
+	config DEFAULT_SECURITY_SELINUX
+		bool "SELinux" if SECURITY_SELINUX=y
+
+	config DEFAULT_SECURITY_SMACK
+		bool "Simplified Mandatory Access Control" if SECURITY_SMACK=y
+
+	config DEFAULT_SECURITY_TOMOYO
+		bool "TOMOYO" if SECURITY_TOMOYO=y
+
+	config DEFAULT_SECURITY_APPARMOR
+		bool "AppArmor" if SECURITY_APPARMOR=y
+	config DEFAULT_SECURITY_DAC
+		bool "Unix Discretionary Access Controls"
+
+endchoice
+
 config LSM
 	string "Ordered list of enabled LSMs"
-	default "yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor"
+	default "yama,loadpin,safesetid,integrity,selinux" if DEFAULT_SECURITY_SELINUX
+	default "yama,loadpin,safesetid,integrity,smack" if DEFAULT_SECURITY_SMACK
+	default "yama,loadpin,safesetid,integrity,tomoyo" if DEFAULT_SECURITY_TOMOYO
+	default "yama,loadpin,safesetid,integrity,apparmor" if DEFAULT_SECURITY_APPARMOR
+	default "yama,loadpin,safesetid,integrity"
 	help
 	  A comma-separated list of LSMs, in initialization order.
 	  Any LSMs left off this list will be ignored. This can be
-- 
1.8.3.1