cgroup: restructure cgroup_procs_write_permission()

Restructure cgroup_procs_write_permission() to make extending
permission logic easier.

This patch doesn't cause any functional changes.

Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index dbfd7028b1c66a13faf5af66902ab5c9212d4aca..d48069ee84c27e2441c43ed37651bdaa9aa25730 100644 (file)
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2363,27 +2363,12 @@ static int cgroup_procs_write_permission(struct task_struct *task,
                                         struct cgroup *dst_cgrp,
                                         struct kernfs_open_file *of)
 {
-       int ret = 0;
-
-       if (cgroup_on_dfl(dst_cgrp)) {
-               struct super_block *sb = of->file->f_path.dentry->d_sb;
-               struct cgroup *cgrp;
-               struct inode *inode;
-
-               spin_lock_irq(&css_set_lock);
-               cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
-               spin_unlock_irq(&css_set_lock);
-
-               while (!cgroup_is_descendant(dst_cgrp, cgrp))
-                       cgrp = cgroup_parent(cgrp);
+       struct super_block *sb = of->file->f_path.dentry->d_sb;
+       struct cgroup *src_cgrp, *com_cgrp;
+       struct inode *inode;
+       int ret;
 
-               ret = -ENOMEM;
-               inode = kernfs_get_inode(sb, cgrp->procs_file.kn);
-               if (inode) {
-                       ret = inode_permission(inode, MAY_WRITE);
-                       iput(inode);
-               }
-       } else {
+       if (!cgroup_on_dfl(dst_cgrp)) {
                const struct cred *cred = current_cred();
                const struct cred *tcred = get_task_cred(task);
 
@@ -2391,14 +2376,38 @@ static int cgroup_procs_write_permission(struct task_struct *task,
                 * even if we're attaching all tasks in the thread group,
                 * we only need to check permissions on one of them.
                 */
-               if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
-                   !uid_eq(cred->euid, tcred->uid) &&
-                   !uid_eq(cred->euid, tcred->suid))
+               if (uid_eq(cred->euid, GLOBAL_ROOT_UID) ||
+                   uid_eq(cred->euid, tcred->uid) ||
+                   uid_eq(cred->euid, tcred->suid))
+                       ret = 0;
+               else
                        ret = -EACCES;
+
                put_cred(tcred);
+               return ret;
        }
 
-       return ret;
+       /* find the source cgroup */
+       spin_lock_irq(&css_set_lock);
+       src_cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
+       spin_unlock_irq(&css_set_lock);
+
+       /* and the common ancestor */
+       com_cgrp = src_cgrp;
+       while (!cgroup_is_descendant(dst_cgrp, com_cgrp))
+               com_cgrp = cgroup_parent(com_cgrp);
+
+       /* %current should be authorized to migrate to the common ancestor */
+       inode = kernfs_get_inode(sb, com_cgrp->procs_file.kn);
+       if (!inode)
+               return -ENOMEM;
+
+       ret = inode_permission(inode, MAY_WRITE);
+       iput(inode);
+       if (ret)
+               return ret;
+
+       return 0;
 }
 
 /*