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
'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>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 0249f4be9b5cf8fefe9885b6093911746d7a9cdd..455689fd19715bc905a3f826bd4a329dbc9a1db8 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -51,6 +51,7 @@
 #include <linux/pid_namespace.h>
 #include <linux/idr.h>
 #include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
+#include <linux/capability.h>
 
 #include <asm/atomic.h>
 
@@ -1555,6 +1556,15 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
                        retval = ss->can_attach(ss, cgrp, tsk, false);
                        if (retval)
                                return retval;
+               } 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;
+                       }
                }
        }
 
@@ -1611,7 +1621,6 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
 static int attach_task_by_pid(struct cgroup *cgrp, u64 pid)
 {
        struct task_struct *tsk;
-       const struct cred *cred = current_cred(), *tcred;
        int ret;
 
        if (pid) {
@@ -1621,14 +1630,6 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid)
                        rcu_read_unlock();
                        return -ESRCH;
                }
-
-               tcred = __task_cred(tsk);
-               if (cred->euid &&
-                   cred->euid != tcred->uid &&
-                   cred->euid != tcred->suid) {
-                       rcu_read_unlock();
-                       return -EACCES;
-               }
                get_task_struct(tsk);
                rcu_read_unlock();
        } else {

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 59e9ef6aab4002e1d99170f50156e733e8f46343..67b155f65a6c944b100a684d651b7a2b65fc3e17 100644 (file)
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -163,6 +163,14 @@ 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.
         *

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index b5cb469d25456b03292d27e22ece4508ddba1ca2..2b637ca37be4b82aea0d7bb3dfbe9cf04d386b45 100644 (file)
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1330,6 +1330,13 @@ static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cont,
        int ret;
        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;
 

diff --git a/kernel/sched.c b/kernel/sched.c
index 9f11c6c784154725068fdbeee135c1d616eadf1b..117b2b4ebbafd2dee46bdae890ec9bfe7566af29 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -10418,6 +10418,15 @@ 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;