+ mm-memcg-v1-account-event-registrations-and-drop-world-writable-cgroupevent_control.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/memcg: v1: account event registrations and drop world-writable cgroup.event_control
has been added to the -mm mm-new branch.  Its filename is
     mm-memcg-v1-account-event-registrations-and-drop-world-writable-cgroupevent_control.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memcg-v1-account-event-registrations-and-drop-world-writable-cgroupevent_control.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
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fixup patches in mm-new.

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------------------------------------------------------
From: Stanislav Fort <stanislav.fort@aisle.com>
Subject: mm/memcg: v1: account event registrations and drop world-writable cgroup.event_control
Date: Fri, 5 Sep 2025 12:38:51 +0300

In cgroup v1, the legacy cgroup.event_control file is world-writable and
allows unprivileged users to register unbounded events and thresholds. 
Each registration allocates kernel memory without capping or memcg
charging, which can be abused to exhaust kernel memory in affected
configurations.

Make the following minimal changes:
- Account allocations with __GFP_ACCOUNT in event and threshold registration.
- Remove CFTYPE_WORLD_WRITABLE from cgroup.event_control to make it
  owner-writable.

This does not affect cgroup v2.  Allocations are still subject to kmem
accounting being enabled, but this reduces unbounded global growth.

Link: https://lkml.kernel.org/r/20250905093851.80596-1-disclosure@aisle.com
Signed-off-by: Stanislav Fort <disclosure@aisle.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol-v1.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/mm/memcontrol-v1.c~mm-memcg-v1-account-event-registrations-and-drop-world-writable-cgroupevent_control
+++ a/mm/memcontrol-v1.c
@@ -761,7 +761,7 @@ static int __mem_cgroup_usage_register_e
 	size = thresholds->primary ? thresholds->primary->size + 1 : 1;
 
 	/* Allocate memory for new array of thresholds */
-	new = kmalloc(struct_size(new, entries, size), GFP_KERNEL);
+	new = kmalloc(struct_size(new, entries, size), GFP_KERNEL_ACCOUNT);
 	if (!new) {
 		ret = -ENOMEM;
 		goto unlock;
@@ -924,7 +924,7 @@ static int mem_cgroup_oom_register_event
 {
 	struct mem_cgroup_eventfd_list *event;
 
-	event = kmalloc(sizeof(*event),	GFP_KERNEL);
+	event = kmalloc(sizeof(*event),	GFP_KERNEL_ACCOUNT);
 	if (!event)
 		return -ENOMEM;
 
@@ -1087,7 +1087,7 @@ static ssize_t memcg_write_event_control
 
 	CLASS(fd, cfile)(cfd);
 
-	event = kzalloc(sizeof(*event), GFP_KERNEL);
+	event = kzalloc(sizeof(*event), GFP_KERNEL_ACCOUNT);
 	if (!event)
 		return -ENOMEM;
 
@@ -2053,7 +2053,7 @@ struct cftype mem_cgroup_legacy_files[]
 	{
 		.name = "cgroup.event_control",		/* XXX: for compat */
 		.write = memcg_write_event_control,
-		.flags = CFTYPE_NO_PREFIX | CFTYPE_WORLD_WRITABLE,
+		.flags = CFTYPE_NO_PREFIX,
 	},
 	{
 		.name = "swappiness",
_

Patches currently in -mm which might be from stanislav.fort@aisle.com are

mm-damon-sysfs-fix-use-after-free-in-state_show.patch
mm-memcg-v1-account-event-registrations-and-drop-world-writable-cgroupevent_control.patch