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>

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index ddd92cec78ed81c44bcfc4d9c530662a179381f2..236fffa9d05e5ed7e904489f5051430b87fe664e 100644 (file)
--- 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,
        },
        {