Casey Schaufler wrote: > On 2/6/2019 2:23 AM, Tetsuo Handa wrote: > > But as I update the documentation ( https://tomoyo.osdn.jp/2.6/chapter-3.html.en#3.6 ), > > I came to think that we should ignore security= parameter when lsm= parameter is specified. > > > > Currently, it is possible to enable TOMOYO and only one of SELinux/Smack/AppArmor. Therefore, > > it is possible to disable only TOMOYO by specifying security=selinux when we want to enable > > only SELinux, by specifying security=smack when we want to enable only Smack, by specifying > > security=apparmor when we want to enable only AppArmor. That is, we can use security= parameter > > in order to specify the other LSM module which should not be disabled. > > > > But when it becomes possible to enable TOMOYO and more than one of SELinux/Smack/AppArmor, > > we will no longer be able to selectively disable one LSM module using security= parameter, for > > security= parameter is intended for specifying only one LSM module which should be enabled. > > That is, we will need to use lsm= parameter in order to selectively disable LSM modules. > > Yes. That is correct. The existing behavior of security= is maintained. But the existing behavior of CONFIG_DEFAULT_SECURITY is not maintained. This might cause a problem like commit e5a3b95f581da62e2054ef79d3be2d383e9ed664 Author: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Date: Sat Feb 14 11:46:56 2009 +0900 TOMOYO: Don't create securityfs entries unless registered. TOMOYO should not create /sys/kernel/security/tomoyo/ interface unless TOMOYO is registered. for Ubuntu users because Ubuntu kernels are built with CONFIG_SECURITY_SELINUX=y CONFIG_SECURITY_SMACK=y CONFIG_SECURITY_TOMOYO=y CONFIG_SECURITY_APPARMOR=y CONFIG_SECURITY_YAMA=y CONFIG_DEFAULT_SECURITY="apparmor" . Due to CONFIG_DEFAULT_SECURITY="apparmor", majority of Ubuntu users are enabling only AppArmor without explicitly specifying "security=apparmor". Currently default CONFIG_LSM setting is "yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor" but Ubuntu kernels would have to be built with non-default CONFIG_LSM setting like "yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo" in order to make sure that AppArmor is by default chosen for the LSM_FLAG_EXCLUSIVE module. Now that TOMOYO becomes a !LSM_FLAG_EXCLUSIVE module, not specifying "security=apparmor" will automatically enable TOMOYO. And majority of Ubuntu users will unexpectedly encounter TOMOYO messages. But removing "tomoyo" from CONFIG_LSM setting in order to save majority of Ubuntu users from unexpectedly encountering TOMOYO messages also has a problem; Ubuntu users who want to enable only TOMOYO from LSM_FLAG_LEGACY_MAJOR modules can specify "security=tomoyo", but Ubuntu users who want to enable TOMOYO and one of SELinux,Smack,AppArmor (including syzbot) will have to explicitly specify "lsm=" because "security=" can't allow enabling multiple LSM_FLAG_LEGACY_MAJOR modules. > The new behavior of lsm= is provided to allow general handling of a list > of security modules. It uses the same form of data as CONFIG_LSM. > > > Then, I think that it is straightforward (and easier to manage) to ignore security= parameter > > when lsm= parameter is specified. > > That reduces flexibility somewhat. If I am debugging security modules > I may want to use lsm= to specify the order while using security= to > identify a specific exclusive module. I could do that using lsm= by > itself, but habits die hard. "lsm=" can be used for identifying a specific exclusive module, and Ubuntu kernels would have to use CONFIG_LSM (or "lsm=") for identifying the default exclusive module (in order to allow enabling both TOMOYO and one of SELinux,Smack,AppArmor at the same time). Since "security=" can't be used for selectively enable/disable more than one of SELinux,Smack,TOMOYO,AppArmor, I think that recommending users to migrate to "lsm=" is the better direction. And ignoring "security=" when "lsm=" is specified is easier to understand.
