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Commit dddee781 authored by Colin Cross's avatar Colin Cross Committed by ivanmeler
Browse files

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>
Signed-off-by: default avatarChatur27 <jasonbright2709@gmail.com>
parent 58d96bde

include/linux/cgroup-defs.h

+2 −1
Original line number Diff line number Diff line
@@ -451,8 +451,9 @@ struct cgroup_subsys { 
	void (*css_released)(struct cgroup_subsys_state *css);

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

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



	int (*allow_attach)(struct cgroup_taskset *tset);

	int (*allow_attach)(struct cgroup_subsys_state *css,

			    struct cgroup_taskset *tset);

	int (*can_attach)(struct cgroup_taskset *tset);

	void (*cancel_attach)(struct cgroup_taskset *tset);

	void (*attach)(struct cgroup_taskset *tset);

kernel/cgroup.c

+36 −2
Original line number Diff line number Diff line
@@ -2844,6 +2844,25 @@ 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;

}



static int cgroup_procs_write_permission(struct task_struct *task,

					 struct cgroup *dst_cgrp,

					 struct kernfs_open_file *of)
@@ -2859,8 +2878,23 @@ 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_SYS_NICE))

	    !ns_capable(tcred->user_ns, CAP_SYS_NICE)) {

		/*

		 * 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(task);

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

		ret = cgroup_allow_attach(dst_cgrp, &tset);

		if (ret)

			ret = -EACCES;

	}



	if (!ret && cgroup_on_dfl(dst_cgrp)) {

		struct super_block *sb = of->file->f_path.dentry->d_sb;