From abfea90e04a07d245ca7e8c95a2ec45d9860eacc Mon Sep 17 00:00:00 2001 From: Stanislav Fort Date: Fri, 5 Sep 2025 12:38:51 +0300 Subject: [PATCH] mm/memcg: v1: account event registrations and drop world-writable cgroup.event_control 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 Acked-by: Roman Gushchin Acked-by: Shakeel Butt Cc: Johannes Weiner Cc: Michal Hocko Cc: Muchun Song Signed-off-by: Andrew Morton --- mm/memcontrol-v1.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c index 4b94731305b9f..6eed14bff7426 100644 --- a/mm/memcontrol-v1.c +++ b/mm/memcontrol-v1.c @@ -761,7 +761,7 @@ static int __mem_cgroup_usage_register_event(struct mem_cgroup *memcg, 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 *memcg, { 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(struct kernfs_open_file *of, 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", -- 2.51.0