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Commit 53b5e2f0 authored by Colin Cross's avatar Colin Cross Committed by Ruchi Kandoi
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cgroup: Add generic cgroup subsystem permission checks 



Rather than using explicit euid == 0 checks when trying to move
tasks into a cgroup via CFS, move permission checks into each
specific cgroup subsystem. If a subsystem does not specify a
'allow_attach' handler, then we fall back to doing our checks
the old way.

Use the 'allow_attach' handler for the 'cpu' cgroup to allow
non-root processes to add arbitrary processes to a 'cpu' cgroup
if it has the CAP_SYS_NICE capability set.

This version of the patch adds a 'allow_attach' handler instead
of reusing the 'can_attach' handler.  If the 'can_attach' handler
is reused, a new cgroup that implements 'can_attach' but not
the permission checks could end up with no permission checks
at all.

Change-Id: Icfa950aa9321d1ceba362061d32dc7dfa2c64f0c
Original-Author: San Mehat <san@google.com>
Signed-off-by: default avatarColin Cross <ccross@android.com>
parent 63351df8

Documentation/cgroups/cgroups.txt

+9 −0
Original line number Diff line number Diff line
@@ -578,6 +578,15 @@ is completely unused; @cgrp->parent is still valid. (Note - can also 
be called for a newly-created cgroup if an error occurs after this

subsystem's create() method has been called for the new cgroup).



int allow_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)

(cgroup_mutex held by caller)



Called prior to moving a task into a cgroup; if the subsystem

returns an error, this will abort the attach operation.  Used

to extend the permission checks - if all subsystems in a cgroup

return 0, the attach will be allowed to proceed, even if the

default permission check (root or same user) fails.



int can_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)

(cgroup_mutex held by caller)

include/linux/cgroup.h

+2 −0
Original line number Diff line number Diff line
@@ -615,6 +615,8 @@ struct cgroup_subsys { 
	void (*css_free)(struct cgroup_subsys_state *css);

	void (*css_reset)(struct cgroup_subsys_state *css);



	int (*allow_attach)(struct cgroup_subsys_state *css,

			    struct cgroup_taskset *tset);

	int (*can_attach)(struct cgroup_subsys_state *css,

			  struct cgroup_taskset *tset);

	void (*cancel_attach)(struct cgroup_subsys_state *css,

kernel/cgroup.c

+36 −3
Original line number Diff line number Diff line
@@ -2346,6 +2346,25 @@ int subsys_cgroup_allow_attach(struct cgroup_subsys_state *css, struct cgroup_ta 
	return 0;

}



static int cgroup_allow_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)

{

	struct cgroup_subsys_state *css;

	int i;

	int ret;



	for_each_css(css, i, cgrp) {

		if (css->ss->allow_attach) {

			ret = css->ss->allow_attach(css, tset);

			if (ret)

				return ret;

		} else {

			return -EACCES;

		}

	}



	return 0;

}



/*

 * Find the task_struct of the task to attach by vpid and pass it along to the

 * function to attach either it or all tasks in its threadgroup. Will lock
@@ -2384,10 +2403,24 @@ retry_find_task: 
		if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&

		    !uid_eq(cred->euid, tcred->uid) &&

		    !uid_eq(cred->euid, tcred->suid)) {

			/*

			 * if the default permission check fails, give each

			 * cgroup a chance to extend the permission check

			 */

			struct cgroup_taskset tset = {

				.src_csets = LIST_HEAD_INIT(tset.src_csets),

				.dst_csets = LIST_HEAD_INIT(tset.dst_csets),

				.csets = &tset.src_csets,

			};

			struct css_set *cset;

			cset = task_css_set(tsk);

			list_add(&cset->mg_node, &tset.src_csets);

			ret = cgroup_allow_attach(cgrp, &tset);

			if (ret) {

				rcu_read_unlock();

			ret = -EACCES;

				goto out_unlock_cgroup;

			}

		}

	} else

		tsk = current;