cgroup: Add generic cgroup subsystem permission checks.
San Mehat [Thu, 21 May 2009 21:10:06 +0000 (14:10 -0700)]
    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
'can_attach' handler, then we fall back to doing our checks the old way.

    This way non-root processes can add arbitrary processes to
a cgroup if all the registered subsystems on that cgroup agree.

    Also change explicit euid == 0 check to CAP_SYS_ADMIN

Signed-off-by: San Mehat <san@google.com>

kernel/cgroup.c
kernel/cgroup_freezer.c
kernel/cpuset.c
kernel/sched.c

index 1d2b6ce..e06035a 100644 (file)
@@ -60,6 +60,7 @@
 #include <linux/eventfd.h>
 #include <linux/poll.h>
 #include <linux/flex_array.h> /* used in cgroup_attach_proc */
+#include <linux/capability.h>
 
 #include <linux/atomic.h>
 
@@ -1842,6 +1843,15 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
                                failed_ss = ss;
                                goto out;
                        }
+               } else if (!capable(CAP_SYS_ADMIN)) {
+                       const struct cred *cred = current_cred(), *tcred;
+
+                       /* No can_attach() - check perms generically */
+                       tcred = __task_cred(tsk);
+                       if (cred->euid != tcred->uid &&
+                           cred->euid != tcred->suid) {
+                               return -EACCES;
+                       }
                }
                if (ss->can_attach_task) {
                        retval = ss->can_attach_task(cgrp, tsk);
index e691818..6ebda1d 100644 (file)
@@ -164,6 +164,14 @@ static int freezer_can_attach(struct cgroup_subsys *ss,
 {
        struct freezer *freezer;
 
+       if ((current != task) && (!capable(CAP_SYS_ADMIN))) {
+               const struct cred *cred = current_cred(), *tcred;
+
+               tcred = __task_cred(task);
+               if (cred->euid != tcred->uid && cred->euid != tcred->suid)
+                       return -EPERM;
+       }
+
        /*
         * Anything frozen can't move or be moved to/from.
         */
index 10131fd..3b23051 100644 (file)
@@ -1373,6 +1373,13 @@ static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cont,
 {
        struct cpuset *cs = cgroup_cs(cont);
 
+       if ((current != task) && (!capable(CAP_SYS_ADMIN))) {
+               const struct cred *cred = current_cred(), *tcred;
+
+               if (cred->euid != tcred->uid && cred->euid != tcred->suid)
+                       return -EPERM;
+       }
        if (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))
                return -ENOSPC;
 
index d0f600c..279d255 100644 (file)
@@ -8967,6 +8967,15 @@ cpu_cgroup_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp)
 static int
 cpu_cgroup_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
 {
+       if ((current != tsk) && (!capable(CAP_SYS_NICE))) {
+               const struct cred *cred = current_cred(), *tcred;
+
+               tcred = __task_cred(tsk);
+
+               if (cred->euid != tcred->uid && cred->euid != tcred->suid)
+                       return -EPERM;
+       }
+
 #ifdef CONFIG_RT_GROUP_SCHED
        if (!sched_rt_can_attach(cgroup_tg(cgrp), tsk))
                return -EINVAL;