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SubjectRe: [PATCH 3/4] cgroup: require write perm on common ancestor when moving processes on the default hierarchy
Hi Tejun,

> -static int cgroup_procs_write_permission(struct task_struct *task)
> +static int cgroup_procs_write_permission(struct task_struct *task,
> + struct cgroup *dst_cgrp,
> + struct kernfs_open_file *of)
> {
> const struct cred *cred = current_cred();
> const struct cred *tcred = get_task_cred(task);
> @@ -2407,6 +2409,26 @@ static int cgroup_procs_write_permission(struct task_struct *task)
> !uid_eq(cred->euid, tcred->suid))
> ret = -EACCES;
>
> + if (cgroup_on_dfl(dst_cgrp)) {

if (!ret && cgroup_on_dfl(dst_cgrp))

> + struct super_block *sb = of->file->f_path.dentry->d_sb;
> + struct cgroup *cgrp;
> + struct inode *inode;
> +
> + down_read(&css_set_rwsem);
> + cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
> + up_read(&css_set_rwsem);
> +
> + while (!cgroup_is_descendant(dst_cgrp, cgrp))
> + cgrp = cgroup_parent(cgrp);
> +
> + ret = -ENOMEM;
> + inode = kernfs_get_inode(sb, cgrp->procs_kn);
> + if (inode) {
> + ret = inode_permission(inode, MAY_WRITE);
> + iput(inode);
> + }
> + }
> +
> put_cred(tcred);
> return ret;
> }



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