| Message ID | 1477013079-23692-1-git-send-email-john.stultz@linaro.org |
|---|---|
| State | New |
| Headers | show |
Hi John, On 10/21/2016 03:24 AM, John Stultz wrote: > This patch adds logic to allows a process to migrate other tasks > between cgroups if they have CAP_SYS_RESOURCE. This appears to be a patch against your previous patch, rather than against mainline. Was that intended? Cheers, Michael > In Android (where this feature originated), the ActivityManager tracks > various application states (TOP_APP, FOREGROUND, BACKGROUND, SYSTEM, > etc), and then as applications change states, the SchedPolicy logic > will migrate the application tasks between different cgroups used > to control the different application states (for example, there is a > background cpuset cgroup which can limit background tasks to stay > on one low-power cpu, and the bg_non_interactive cpuctrl cgroup can > then further limit those background tasks to a small percentage of > that one cpu's cpu time). > > However, for security reasons, Android doesn't want to make the > system_server (the process that runs the ActivityManager and > SchedPolicy logic), run as root. So in the Android common.git > kernel, they have some logic to allow cgroups to loosen their > permissions so CAP_SYS_NICE tasks can migrate other tasks between > cgroups. > > I feel the approach taken there overloads CAP_SYS_NICE a bit much, > and is maybe more complicated then needed. > > So this patch, as suggested by Michael Kerrisk, simply adds a > check for CAP_SYS_RESOURCE. > > I've tested this with AOSP master, and this seems to work well > as Zygote and system_server already use CAP_SYS_RESOURCE. I've > also submitted patches against the android-4.4 kernel to change > it to use CAP_SYS_RESOURCE, and the Android developers have > seemed ok with this change. > > Thouhts and feedback would be appreciated! > > Cc: Tejun Heo <tj@kernel.org> > Cc: Li Zefan <lizefan@huawei.com> > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: cgroups@vger.kernel.org > Cc: Android Kernel Team <kernel-team@android.com> > Cc: Rom Lemarchand <romlem@android.com> > Cc: Colin Cross <ccross@android.com> > Cc: Dmitry Shmidt <dimitrysh@google.com> > Cc: Todd Kjos <tkjos@google.com> > Cc: Christian Poetzsch <christian.potzsch@imgtec.com> > Cc: Amit Pundir <amit.pundir@linaro.org> > Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com> > Cc: Kees Cook <keescook@chromium.org> > Cc: Serge E. Hallyn <serge@hallyn.com> > Cc: linux-api@vger.kernel.org > Signed-off-by: John Stultz <john.stultz@linaro.org> > --- > v2: Renamed to just CAP_CGROUP_MIGRATE as reccomended by Tejun > v3: Switched to just using CAP_SYS_RESOURCE as suggested by Michael > --- > kernel/cgroup.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/cgroup.c b/kernel/cgroup.c > index 09f84d2..866059a 100644 > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -2857,7 +2857,7 @@ static int cgroup_procs_write_permission(struct task_struct *task, > if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) && > !uid_eq(cred->euid, tcred->uid) && > !uid_eq(cred->euid, tcred->suid) && > - !ns_capable(tcred->user_ns, CAP_CGROUP_MIGRATE)) > + !ns_capable(tcred->user_ns, CAP_SYS_RESOURCE)) > ret = -EACCES; > > if (!ret && cgroup_on_dfl(dst_cgrp)) { > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
Quoting John Stultz (john.stultz@linaro.org): > This patch adds logic to allows a process to migrate other tasks > between cgroups if they have CAP_SYS_RESOURCE. Hi, fwiw this seems to me a reasonable choice, that is, giving a task CAP_SYS_RESOURCE to be allow it to write to the procs file doesn't seem like giving it too much. +1 from me. So long as the Android folks don't have a reason why this won't work for them, Acked-by: Serge Hallyn <serge@hallyn.com> -serge > In Android (where this feature originated), the ActivityManager tracks > various application states (TOP_APP, FOREGROUND, BACKGROUND, SYSTEM, > etc), and then as applications change states, the SchedPolicy logic > will migrate the application tasks between different cgroups used > to control the different application states (for example, there is a > background cpuset cgroup which can limit background tasks to stay > on one low-power cpu, and the bg_non_interactive cpuctrl cgroup can > then further limit those background tasks to a small percentage of > that one cpu's cpu time). > > However, for security reasons, Android doesn't want to make the > system_server (the process that runs the ActivityManager and > SchedPolicy logic), run as root. So in the Android common.git > kernel, they have some logic to allow cgroups to loosen their > permissions so CAP_SYS_NICE tasks can migrate other tasks between > cgroups. > > I feel the approach taken there overloads CAP_SYS_NICE a bit much, > and is maybe more complicated then needed. > > So this patch, as suggested by Michael Kerrisk, simply adds a > check for CAP_SYS_RESOURCE. > > I've tested this with AOSP master, and this seems to work well > as Zygote and system_server already use CAP_SYS_RESOURCE. I've > also submitted patches against the android-4.4 kernel to change > it to use CAP_SYS_RESOURCE, and the Android developers have > seemed ok with this change. > > Thouhts and feedback would be appreciated! > > Cc: Tejun Heo <tj@kernel.org> > Cc: Li Zefan <lizefan@huawei.com> > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: cgroups@vger.kernel.org > Cc: Android Kernel Team <kernel-team@android.com> > Cc: Rom Lemarchand <romlem@android.com> > Cc: Colin Cross <ccross@android.com> > Cc: Dmitry Shmidt <dimitrysh@google.com> > Cc: Todd Kjos <tkjos@google.com> > Cc: Christian Poetzsch <christian.potzsch@imgtec.com> > Cc: Amit Pundir <amit.pundir@linaro.org> > Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com> > Cc: Kees Cook <keescook@chromium.org> > Cc: Serge E. Hallyn <serge@hallyn.com> > Cc: linux-api@vger.kernel.org > Signed-off-by: John Stultz <john.stultz@linaro.org> > --- > v2: Renamed to just CAP_CGROUP_MIGRATE as reccomended by Tejun > v3: Switched to just using CAP_SYS_RESOURCE as suggested by Michael > --- > kernel/cgroup.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/cgroup.c b/kernel/cgroup.c > index 09f84d2..866059a 100644 > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -2857,7 +2857,7 @@ static int cgroup_procs_write_permission(struct task_struct *task, > if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) && > !uid_eq(cred->euid, tcred->uid) && > !uid_eq(cred->euid, tcred->suid) && > - !ns_capable(tcred->user_ns, CAP_CGROUP_MIGRATE)) > + !ns_capable(tcred->user_ns, CAP_SYS_RESOURCE)) > ret = -EACCES; > > if (!ret && cgroup_on_dfl(dst_cgrp)) { > -- > 2.7.4
On Thu, Oct 20, 2016 at 11:42 PM, Michael Kerrisk (man-pages) <mtk.manpages@gmail.com> wrote: > Hi John, > > On 10/21/2016 03:24 AM, John Stultz wrote: >> This patch adds logic to allows a process to migrate other tasks >> between cgroups if they have CAP_SYS_RESOURCE. > > This appears to be a patch against your previous patch, > rather than against mainline. Was that intended? Heh. Definitely not. Apologies. I thought I had folded things down (and the real patch is a similar looking one-liner). I'll re-send the proper patch on monday. :) thanks -john
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 09f84d2..866059a 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2857,7 +2857,7 @@ static int cgroup_procs_write_permission(struct task_struct *task, if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) && !uid_eq(cred->euid, tcred->uid) && !uid_eq(cred->euid, tcred->suid) && - !ns_capable(tcred->user_ns, CAP_CGROUP_MIGRATE)) + !ns_capable(tcred->user_ns, CAP_SYS_RESOURCE)) ret = -EACCES; if (!ret && cgroup_on_dfl(dst_cgrp)) {
This patch adds logic to allows a process to migrate other tasks between cgroups if they have CAP_SYS_RESOURCE. In Android (where this feature originated), the ActivityManager tracks various application states (TOP_APP, FOREGROUND, BACKGROUND, SYSTEM, etc), and then as applications change states, the SchedPolicy logic will migrate the application tasks between different cgroups used to control the different application states (for example, there is a background cpuset cgroup which can limit background tasks to stay on one low-power cpu, and the bg_non_interactive cpuctrl cgroup can then further limit those background tasks to a small percentage of that one cpu's cpu time). However, for security reasons, Android doesn't want to make the system_server (the process that runs the ActivityManager and SchedPolicy logic), run as root. So in the Android common.git kernel, they have some logic to allow cgroups to loosen their permissions so CAP_SYS_NICE tasks can migrate other tasks between cgroups. I feel the approach taken there overloads CAP_SYS_NICE a bit much, and is maybe more complicated then needed. So this patch, as suggested by Michael Kerrisk, simply adds a check for CAP_SYS_RESOURCE. I've tested this with AOSP master, and this seems to work well as Zygote and system_server already use CAP_SYS_RESOURCE. I've also submitted patches against the android-4.4 kernel to change it to use CAP_SYS_RESOURCE, and the Android developers have seemed ok with this change. Thouhts and feedback would be appreciated! Cc: Tejun Heo <tj@kernel.org> Cc: Li Zefan <lizefan@huawei.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: cgroups@vger.kernel.org Cc: Android Kernel Team <kernel-team@android.com> Cc: Rom Lemarchand <romlem@android.com> Cc: Colin Cross <ccross@android.com> Cc: Dmitry Shmidt <dimitrysh@google.com> Cc: Todd Kjos <tkjos@google.com> Cc: Christian Poetzsch <christian.potzsch@imgtec.com> Cc: Amit Pundir <amit.pundir@linaro.org> Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com> Cc: Kees Cook <keescook@chromium.org> Cc: Serge E. Hallyn <serge@hallyn.com> Cc: linux-api@vger.kernel.org Signed-off-by: John Stultz <john.stultz@linaro.org> --- v2: Renamed to just CAP_CGROUP_MIGRATE as reccomended by Tejun v3: Switched to just using CAP_SYS_RESOURCE as suggested by Michael --- kernel/cgroup.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) -- 2.7.4