[PATCH v5 4/6] cgroup: add cgroup_may_write() helper

Christian Brauner
2020-01-21T15:48:42Z

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>
---
/* v1 */
patch not present

/* v2 */
patch not present

/* v3 */
patch not present

/* v4 */
Link: https://lore.kernel.org/r/20200117181219.14542-5-christian.brauner@ubuntu.com
patch introduced

/* v5 */
unchanged
---
kernel/cgroup/cgroup.c | 24 +++++++++++++++++-------
1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index ce2d5b8aa19f..636fe3d46d2d 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4649,13 +4649,28 @@ static int cgroup_procs_show(struct seq_file *s, void *v)
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,
struct cgroup *dst_cgrp,
struct super_block *sb)
{
struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
struct cgroup *com_cgrp = src_cgrp;
- struct inode *inode;
int ret;

lockdep_assert_held(&cgroup_mutex);
@@ -4665,12 +4680,7 @@ static int cgroup_procs_write_permission(struct cgroup *src_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);
+ ret = cgroup_may_write(com_cgrp, sb);
if (ret)
return ret;

--
2.25.0