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: Colin Cross <ccross@android.com>
diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index 8e74980..594ff17 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -592,6 +592,15 @@
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)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index bb627e0..a2ed0cd 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -447,6 +447,7 @@
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);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 0de8160..0d4bff5 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2119,6 +2119,24 @@
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 @@
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;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 819719b..6a084db 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7633,6 +7633,23 @@
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 @@
.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,