cgroup: replace cftype->mode with CFTYPE_WORLD_WRITABLE
cftype->mode allows controllers to give arbitrary permissions to
interface knobs. Except for "cgroup.event_control", the existing uses
are spurious.
* Some explicitly specify S_IRUGO | S_IWUSR even though that's the
default.
* "cpuset.memory_pressure" specifies S_IRUGO while also setting a
write callback which returns -EACCES. All it needs to do is simply
not setting a write callback.
"cgroup.event_control" uses cftype->mode to make the file
world-writable. It's a misdesigned interface and we don't want
controllers to be tweaking interface file permissions in general.
This patch removes cftype->mode and all its spurious uses and
implements CFTYPE_WORLD_WRITABLE for "cgroup.event_control" which is
marked as compatibility-only.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index d95cc88..10d814b 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -76,6 +76,7 @@
CFTYPE_ONLY_ON_ROOT = (1 << 0), /* only create on root cgrp */
CFTYPE_NOT_ON_ROOT = (1 << 1), /* don't create on root cgrp */
CFTYPE_NO_PREFIX = (1 << 3), /* (DON'T USE FOR NEW FILES) no subsys prefix */
+ CFTYPE_WORLD_WRITABLE = (1 << 4), /* (DON'T USE FOR NEW FILES) S_IWUGO */
/* internal flags, do not use outside cgroup core proper */
__CFTYPE_ONLY_ON_DFL = (1 << 16), /* only on default hierarchy */
@@ -324,11 +325,6 @@
*/
char name[MAX_CFTYPE_NAME];
unsigned long private;
- /*
- * If not 0, file mode is set to this value, otherwise it will
- * be figured out automatically
- */
- umode_t mode;
/*
* The maximum length of string, excluding trailing nul, that can
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 75eba25..5031edc 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1139,23 +1139,21 @@
* cgroup_file_mode - deduce file mode of a control file
* @cft: the control file in question
*
- * returns cft->mode if ->mode is not 0
- * returns S_IRUGO|S_IWUSR if it has both a read and a write handler
- * returns S_IRUGO if it has only a read handler
- * returns S_IWUSR if it has only a write hander
+ * S_IRUGO for read, S_IWUSR for write.
*/
static umode_t cgroup_file_mode(const struct cftype *cft)
{
umode_t mode = 0;
- if (cft->mode)
- return cft->mode;
-
if (cft->read_u64 || cft->read_s64 || cft->seq_show)
mode |= S_IRUGO;
- if (cft->write_u64 || cft->write_s64 || cft->write)
- mode |= S_IWUSR;
+ if (cft->write_u64 || cft->write_s64 || cft->write) {
+ if (cft->flags & CFTYPE_WORLD_WRITABLE)
+ mode |= S_IWUGO;
+ else
+ mode |= S_IWUSR;
+ }
return mode;
}
@@ -4371,7 +4369,6 @@
.seq_show = cgroup_pidlist_show,
.private = CGROUP_FILE_PROCS,
.write = cgroup_procs_write,
- .mode = S_IRUGO | S_IWUSR,
},
{
.name = "cgroup.controllers",
@@ -4406,7 +4403,6 @@
.seq_show = cgroup_pidlist_show,
.private = CGROUP_FILE_PROCS,
.write = cgroup_procs_write,
- .mode = S_IRUGO | S_IWUSR,
},
{
.name = "cgroup.clone_children",
@@ -4426,7 +4422,6 @@
.seq_show = cgroup_pidlist_show,
.private = CGROUP_FILE_TASKS,
.write = cgroup_tasks_write,
- .mode = S_IRUGO | S_IWUSR,
},
{
.name = "notify_on_release",
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 20eedd8..312961e 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1597,9 +1597,6 @@
case FILE_MEMORY_PRESSURE_ENABLED:
cpuset_memory_pressure_enabled = !!val;
break;
- case FILE_MEMORY_PRESSURE:
- retval = -EACCES;
- break;
case FILE_SPREAD_PAGE:
retval = update_flag(CS_SPREAD_PAGE, cs, val);
break;
@@ -1866,9 +1863,6 @@
{
.name = "memory_pressure",
.read_u64 = cpuset_read_u64,
- .write_u64 = cpuset_write_u64,
- .private = FILE_MEMORY_PRESSURE,
- .mode = S_IRUGO,
},
{
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b35c4cc..e672f26 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4060,8 +4060,7 @@
{
.name = "cgroup.event_control", /* XXX: for compat */
.write = memcg_write_event_control,
- .flags = CFTYPE_NO_PREFIX,
- .mode = S_IWUGO,
+ .flags = CFTYPE_NO_PREFIX | CFTYPE_WORLD_WRITABLE,
},
{
.name = "swappiness",