[Devel] [PATCH RHEL10 COMMIT] memcg: guard mm_overdraft() against NULL memcg (cgroup_disable=memory)

[Konstantin Khorenko]

The commit is pushed to "branch-rh10-6.12.0-211.16.1.12.x.vz10-ovz" and will appear at git at bitbucket.org:openvz/vzkernel.git
after rh10-6.12.0-211.16.1.el10
------>
commit 5044f47a9e029a7f13242a7253b549d05be437cb
Author: Konstantin Khorenko <khorenko at virtuozzo.com>
Date:   Wed Jun 3 23:56:13 2026 +0200

    memcg: guard mm_overdraft() against NULL memcg (cgroup_disable=memory)
    
    get_mem_cgroup_from_mm() returns NULL when mem_cgroup_disabled() is true
    (e.g. the kernel was booted with "cgroup_disable=memory"). mm_overdraft()
    dereferenced the result unconditionally:
    
            memcg = get_mem_cgroup_from_mm(mm);
            overdraft = memcg->overdraft;     /* NULL deref */
            css_put(&memcg->css);
    
    It is called from oom_badness() (*overdraft = mm_overdraft(p->mm)) on
    every OOM scoring pass, so any OOM kill on a memory-cgroup-disabled
    kernel NULL-derefs. Return 0 (no overdraft) when memcg is NULL.
    
    Fixes: 0ba4e907e1ae ("memcg: add oom_guarantee")
    https://virtuozzo.atlassian.net/browse/VSTOR-132310
    Feature: mm/oom: OOM guarantee feature
    Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
---
 include/linux/memcontrol.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 23ab42e5978e..bf2440e36941 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -907,6 +907,8 @@ static inline unsigned long mm_overdraft(struct mm_struct *mm)
 	unsigned long overdraft;
 
 	memcg = get_mem_cgroup_from_mm(mm);
+	if (!memcg)
+		return 0;
 	overdraft = memcg->overdraft;
 	css_put(&memcg->css);