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cgroup: add cgroup_may_write() helper 

Add a cgroup_may_write() helper which we can use in the
CLONE_INTO_CGROUP patch series to verify that we can write to the
destination cgroup.

Cc: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: cgroups@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Christian Brauner 2020-02-05 14:26:21 +01:00 committed by Tejun Heo
parent 5a5cf5cb30
commit f3553220d4
1 changed files with 17 additions and 7 deletions
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24
kernel/cgroup/cgroup.c
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@ -4654,13 +4654,28 @@ static int cgroup_procs_show(struct seq_file *s, void *v)
return 0; return 0;
} }
static int cgroup_may_write(const struct cgroup *cgrp, struct super_block *sb)
{
int ret;
struct inode *inode;
lockdep_assert_held(&cgroup_mutex);
inode = kernfs_get_inode(sb, cgrp->procs_file.kn);
if (!inode)
return -ENOMEM;
ret = inode_permission(inode, MAY_WRITE);
iput(inode);
return ret;
}
static int cgroup_procs_write_permission(struct cgroup *src_cgrp, static int cgroup_procs_write_permission(struct cgroup *src_cgrp,
struct cgroup *dst_cgrp, struct cgroup *dst_cgrp,
struct super_block *sb) struct super_block *sb)
{ {
struct cgroup_namespace *ns = current->nsproxy->cgroup_ns; struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
struct cgroup *com_cgrp = src_cgrp; struct cgroup *com_cgrp = src_cgrp;
struct inode *inode;
int ret; int ret;
lockdep_assert_held(&cgroup_mutex); lockdep_assert_held(&cgroup_mutex);
@ -4670,12 +4685,7 @@ static int cgroup_procs_write_permission(struct cgroup *src_cgrp,
com_cgrp = cgroup_parent(com_cgrp); com_cgrp = cgroup_parent(com_cgrp);
/* %current should be authorized to migrate to the common ancestor */ /* %current should be authorized to migrate to the common ancestor */
inode = kernfs_get_inode(sb, com_cgrp->procs_file.kn); ret = cgroup_may_write(com_cgrp, sb);
if (!inode)
return -ENOMEM;
ret = inode_permission(inode, MAY_WRITE);
iput(inode);
if (ret) if (ret)
return ret; return ret;