cgroup files: convert devcgroup_access_write() into a cgroup write_string() handler

This patch converts devcgroup_access_write() from a raw file handler
into a handler for the cgroup write_string() method. This allows some
boilerplate copying/locking/checking to be removed and simplifies the
cleanup path, since these functions are performed by the cgroups
framework before calling the handler.

Signed-off-by: Paul Menage <menage@google.com>
Cc: Paul Jackson <pj@sgi.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Balbir Singh <balbir@in.ibm.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 38 insertions, 63 deletions

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index ddd92cec78ed..236fffa9d05e 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -59,6 +59,11 @@ static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
         return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id));
 }
 
+static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
+{
+        return css_to_devcgroup(task_subsys_state(task, devices_subsys_id));
+}
+
 struct cgroup_subsys devices_subsys;
 
 static int devcgroup_can_attach(struct cgroup_subsys *ss,
@@ -312,10 +317,10 @@ static int may_access_whitelist(struct dev_cgroup *c,
  * when adding a new allow rule to a device whitelist, the rule
  * must be allowed in the parent device
  */
-static int parent_has_perm(struct cgroup *childcg,
+static int parent_has_perm(struct dev_cgroup *childcg,
                                   struct dev_whitelist_item *wh)
 {
-        struct cgroup *pcg = childcg->parent;
+        struct cgroup *pcg = childcg->css.cgroup->parent;
         struct dev_cgroup *parent;
         int ret;
 
@@ -341,39 +346,18 @@ static int parent_has_perm(struct cgroup *childcg,
  * new access is only allowed if you're in the top-level cgroup, or your
  * parent cgroup has the access you're asking for.
  */
-static ssize_t devcgroup_access_write(struct cgroup *cgroup, struct cftype *cft,
-                                struct file *file, const char __user *userbuf,
-                                size_t nbytes, loff_t *ppos)
+static int devcgroup_update_access(struct dev_cgroup *devcgroup,
+                                   int filetype, const char *buffer)
 {
-        struct cgroup *cur_cgroup;
-        struct dev_cgroup *devcgroup, *cur_devcgroup;
-        int filetype = cft->private;
-        char *buffer, *b;
+        struct dev_cgroup *cur_devcgroup;
+        const char *b;
         int retval = 0, count;
         struct dev_whitelist_item wh;
 
         if (!capable(CAP_SYS_ADMIN))
                 return -EPERM;
 
-        devcgroup = cgroup_to_devcgroup(cgroup);
-        cur_cgroup = task_cgroup(current, devices_subsys.subsys_id);
-        cur_devcgroup = cgroup_to_devcgroup(cur_cgroup);
-
-        buffer = kmalloc(nbytes+1, GFP_KERNEL);
-        if (!buffer)
-                return -ENOMEM;
-
-        if (copy_from_user(buffer, userbuf, nbytes)) {
-                retval = -EFAULT;
-                goto out1;
-        }
-        buffer[nbytes] = 0;     /* nul-terminate */
-
-        cgroup_lock();
-        if (cgroup_is_removed(cgroup)) {
-                retval = -ENODEV;
-                goto out2;
-        }
+        cur_devcgroup = task_devcgroup(current);
 
         memset(&wh, 0, sizeof(wh));
         b = buffer;
@@ -392,14 +376,11 @@ static ssize_t devcgroup_access_write(struct cgroup *cgroup, struct cftype *cft,
                 wh.type = DEV_CHAR;
                 break;
         default:
-                retval = -EINVAL;
-                goto out2;
+                return -EINVAL;
         }
         b++;
-        if (!isspace(*b)) {
-                retval = -EINVAL;
-                goto out2;
-        }
+        if (!isspace(*b))
+                return -EINVAL;
         b++;
         if (*b == '*') {
                 wh.major = ~0;
@@ -411,13 +392,10 @@ static ssize_t devcgroup_access_write(struct cgroup *cgroup, struct cftype *cft,
                         b++;
                 }
         } else {
-                retval = -EINVAL;
-                goto out2;
-        }
-        if (*b != ':') {
-                retval = -EINVAL;
-                goto out2;
+                return -EINVAL;
         }
+        if (*b != ':')
+                return -EINVAL;
         b++;
 
         /* read minor */
@@ -431,13 +409,10 @@ static ssize_t devcgroup_access_write(struct cgroup *cgroup, struct cftype *cft,
                         b++;
                 }
         } else {
-                retval = -EINVAL;
-                goto out2;
-        }
-        if (!isspace(*b)) {
-                retval = -EINVAL;
-                goto out2;
+                return -EINVAL;
         }
+        if (!isspace(*b))
+                return -EINVAL;
         for (b++, count = 0; count < 3; count++, b++) {
                 switch (*b) {
                 case 'r':
@@ -454,8 +429,7 @@ static ssize_t devcgroup_access_write(struct cgroup *cgroup, struct cftype *cft,
                         count = 3;
                         break;
                 default:
-                        retval = -EINVAL;
-                        goto out2;
+                        return -EINVAL;
                 }
         }
 
@@ -463,38 +437,39 @@ handle:
         retval = 0;
         switch (filetype) {
         case DEVCG_ALLOW:
-                if (!parent_has_perm(cgroup, &wh))
-                        retval = -EPERM;
-                else
-                        retval = dev_whitelist_add(devcgroup, &wh);
-                break;
+                if (!parent_has_perm(devcgroup, &wh))
+                        return -EPERM;
+                return dev_whitelist_add(devcgroup, &wh);
         case DEVCG_DENY:
                 dev_whitelist_rm(devcgroup, &wh);
                 break;
         default:
-                retval = -EINVAL;
-                goto out2;
+                return -EINVAL;
         }
+        return 0;
+}
 
-        if (retval == 0)
-                retval = nbytes;
-
-out2:
+static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
+                                  const char *buffer)
+{
+        int retval;
+        if (!cgroup_lock_live_group(cgrp))
+                return -ENODEV;
+        retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
+                                         cft->private, buffer);
         cgroup_unlock();
-out1:
-        kfree(buffer);
         return retval;
 }
 
 static struct cftype dev_cgroup_files[] = {
         {
                 .name = "allow",
-                .write  = devcgroup_access_write,
+                .write_string  = devcgroup_access_write,
                 .private = DEVCG_ALLOW,
         },
         {
                 .name = "deny",
-                .write = devcgroup_access_write,
+                .write_string = devcgroup_access_write,
                 .private = DEVCG_DENY,
         },
         {