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cgroup: Add generic cgroup subsystem permission checks

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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: Colin Cross <ccross@android.com>
This commit is contained in:
Colin Cross 2011-07-12 19:53:24 -07:00
parent c0f6fa8c40
commit 4a12178d3d
4 changed files with 58 additions and 3 deletions
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9
Documentation/cgroups/cgroups.txt
View file

@ -592,6 +592,15 @@ there are not tasks in the cgroup. If pre_destroy() returns error code,
rmdir() will fail with it. From this behavior, pre_destroy() can be
called multiple times against a 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)

1
include/linux/cgroup.h
View file

@ -447,6 +447,7 @@ struct cgroup_subsys {
struct cgroup_subsys_state *(*create)(struct cgroup *cgrp);
int (*pre_destroy)(struct cgroup *cgrp);
void (*destroy)(struct cgroup *cgrp);
int (*allow_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);
int (*can_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);
void (*cancel_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);
void (*attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);

33
kernel/cgroup.c
View file

@ -2119,6 +2119,24 @@ out_free_group_list:
return retval;
}
static int cgroup_allow_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
{
struct cgroup_subsys *ss;
int ret;
for_each_subsys(cgrp->root, ss) {
if (ss->allow_attach) {
ret = ss->allow_attach(cgrp, 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
@ -2150,9 +2168,18 @@ retry_find_task:
if (cred->euid &&
cred->euid != tcred->uid &&
cred->euid != tcred->suid) {
rcu_read_unlock();
ret = -EACCES;
goto out_unlock_cgroup;
/*
* if the default permission check fails, give each
* cgroup a chance to extend the permission check
*/
struct cgroup_taskset tset = { };
tset.single.task = tsk;
tset.single.cgrp = cgrp;
ret = cgroup_allow_attach(cgrp, &tset);
if (ret) {
rcu_read_unlock();
goto out_unlock_cgroup;
}
}
} else
tsk = current;

18
kernel/sched/core.c
View file

@ -7633,6 +7633,23 @@ static void cpu_cgroup_destroy(struct cgroup *cgrp)
sched_destroy_group(tg);
}
static int
cpu_cgroup_allow_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
{
const struct cred *cred = current_cred(), *tcred;
struct task_struct *task;
cgroup_taskset_for_each(task, cgrp, tset) {
tcred = __task_cred(task);
if ((current != task) && !capable(CAP_SYS_NICE) &&
cred->euid != tcred->uid && cred->euid != tcred->suid)
return -EACCES;
}
return 0;
}
static int cpu_cgroup_can_attach(struct cgroup *cgrp,
struct cgroup_taskset *tset)
{
@ -7994,6 +8011,7 @@ struct cgroup_subsys cpu_cgroup_subsys = {
.destroy = cpu_cgroup_destroy,
.can_attach = cpu_cgroup_can_attach,
.attach = cpu_cgroup_attach,
.allow_attach = cpu_cgroup_allow_attach,
.exit = cpu_cgroup_exit,
.populate = cpu_cgroup_populate,
.subsys_id = cpu_cgroup_subsys_id,