Commit 99a2ef50 authored by Chen Ridong's avatar Chen Ridong Committed by Tejun Heo
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cgroup/dmem: avoid pool UAF 



An UAF issue was observed:

BUG: KASAN: slab-use-after-free in page_counter_uncharge+0x65/0x150
Write of size 8 at addr ffff888106715440 by task insmod/527

CPU: 4 UID: 0 PID: 527 Comm: insmod    6.19.0-rc7-next-20260129+ #11
Tainted: [O]=OOT_MODULE
Call Trace:
<TASK>
dump_stack_lvl+0x82/0xd0
kasan_report+0xca/0x100
kasan_check_range+0x39/0x1c0
page_counter_uncharge+0x65/0x150
dmem_cgroup_uncharge+0x1f/0x260

Allocated by task 527:

Freed by task 0:

The buggy address belongs to the object at ffff888106715400
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 64 bytes inside of
freed 512-byte region [ffff888106715400, ffff888106715600)

The buggy address belongs to the physical page:

Memory state around the buggy address:
ffff888106715300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888106715380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888106715400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
				     ^
ffff888106715480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888106715500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

The issue occurs because a pool can still be held by a caller after its
associated memory region is unregistered. The current implementation frees
the pool even if users still hold references to it (e.g., before uncharge
operations complete).

This patch adds a reference counter to each pool, ensuring that a pool is
only freed when its reference count drops to zero.

Fixes: b168ed45 ("kernel/cgroup: Add "dmem" memory accounting cgroup")
Cc: stable@vger.kernel.org # v6.14+
Signed-off-by: default avatarChen Ridong <chenridong@huawei.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 592a6821

kernel/cgroup/dmem.c

+58 −2
Original line number Diff line number Diff line
@@ -14,6 +14,7 @@ 
#include <linux/mutex.h>

#include <linux/page_counter.h>

#include <linux/parser.h>

#include <linux/refcount.h>

#include <linux/rculist.h>

#include <linux/slab.h>
@@ -71,7 +72,9 @@ struct dmem_cgroup_pool_state { 
	struct rcu_head rcu;



	struct page_counter cnt;

	struct dmem_cgroup_pool_state *parent;



	refcount_t ref;

	bool inited;

};
@@ -88,6 +91,9 @@ struct dmem_cgroup_pool_state { 
static DEFINE_SPINLOCK(dmemcg_lock);

static LIST_HEAD(dmem_cgroup_regions);



static void dmemcg_free_region(struct kref *ref);

static void dmemcg_pool_free_rcu(struct rcu_head *rcu);



static inline struct dmemcg_state *

css_to_dmemcs(struct cgroup_subsys_state *css)

{
@@ -104,10 +110,38 @@ static struct dmemcg_state *parent_dmemcs(struct dmemcg_state *cg) 
	return cg->css.parent ? css_to_dmemcs(cg->css.parent) : NULL;

}



static void dmemcg_pool_get(struct dmem_cgroup_pool_state *pool)

{

	refcount_inc(&pool->ref);

}



static bool dmemcg_pool_tryget(struct dmem_cgroup_pool_state *pool)

{

	return refcount_inc_not_zero(&pool->ref);

}



static void dmemcg_pool_put(struct dmem_cgroup_pool_state *pool)

{

	if (!refcount_dec_and_test(&pool->ref))

		return;



	call_rcu(&pool->rcu, dmemcg_pool_free_rcu);

}



static void dmemcg_pool_free_rcu(struct rcu_head *rcu)

{

	struct dmem_cgroup_pool_state *pool = container_of(rcu, typeof(*pool), rcu);



	if (pool->parent)

		dmemcg_pool_put(pool->parent);

	kref_put(&pool->region->ref, dmemcg_free_region);

	kfree(pool);

}



static void free_cg_pool(struct dmem_cgroup_pool_state *pool)

{

	list_del(&pool->region_node);

	kfree(pool);

	dmemcg_pool_put(pool);

}



static void
@@ -342,6 +376,12 @@ alloc_pool_single(struct dmemcg_state *dmemcs, struct dmem_cgroup_region *region 
	page_counter_init(&pool->cnt,

			  ppool ? &ppool->cnt : NULL, true);

	reset_all_resource_limits(pool);

	refcount_set(&pool->ref, 1);

	kref_get(&region->ref);

	if (ppool && !pool->parent) {

		pool->parent = ppool;

		dmemcg_pool_get(ppool);

	}



	list_add_tail_rcu(&pool->css_node, &dmemcs->pools);

	list_add_tail(&pool->region_node, &region->pools);
@@ -389,6 +429,10 @@ get_cg_pool_locked(struct dmemcg_state *dmemcs, struct dmem_cgroup_region *regio 


		/* Fix up parent links, mark as inited. */

		pool->cnt.parent = &ppool->cnt;

		if (ppool && !pool->parent) {

			pool->parent = ppool;

			dmemcg_pool_get(ppool);

		}

		pool->inited = true;



		pool = ppool;
@@ -435,6 +479,8 @@ void dmem_cgroup_unregister_region(struct dmem_cgroup_region *region) 


	list_for_each_entry_safe(pool, next, &region->pools, region_node) {

		list_del_rcu(&pool->css_node);

		list_del(&pool->region_node);

		dmemcg_pool_put(pool);

	}



	/*
@@ -515,8 +561,10 @@ static struct dmem_cgroup_region *dmemcg_get_region_by_name(const char *name) 
 */

void dmem_cgroup_pool_state_put(struct dmem_cgroup_pool_state *pool)

{

	if (pool)

	if (pool) {

		css_put(&pool->cs->css);

		dmemcg_pool_put(pool);

	}

}

EXPORT_SYMBOL_GPL(dmem_cgroup_pool_state_put);
@@ -530,6 +578,8 @@ get_cg_pool_unlocked(struct dmemcg_state *cg, struct dmem_cgroup_region *region) 
	pool = find_cg_pool_locked(cg, region);

	if (pool && !READ_ONCE(pool->inited))

		pool = NULL;

	if (pool && !dmemcg_pool_tryget(pool))

		pool = NULL;

	rcu_read_unlock();



	while (!pool) {
@@ -538,6 +588,8 @@ get_cg_pool_unlocked(struct dmemcg_state *cg, struct dmem_cgroup_region *region) 
			pool = get_cg_pool_locked(cg, region, &allocpool);

		else

			pool = ERR_PTR(-ENODEV);

		if (!IS_ERR(pool))

			dmemcg_pool_get(pool);

		spin_unlock(&dmemcg_lock);



		if (pool == ERR_PTR(-ENOMEM)) {
@@ -573,6 +625,7 @@ void dmem_cgroup_uncharge(struct dmem_cgroup_pool_state *pool, u64 size) 


	page_counter_uncharge(&pool->cnt, size);

	css_put(&pool->cs->css);

	dmemcg_pool_put(pool);

}

EXPORT_SYMBOL_GPL(dmem_cgroup_uncharge);
@@ -624,7 +677,9 @@ int dmem_cgroup_try_charge(struct dmem_cgroup_region *region, u64 size, 
		if (ret_limit_pool) {

			*ret_limit_pool = container_of(fail, struct dmem_cgroup_pool_state, cnt);

			css_get(&(*ret_limit_pool)->cs->css);

			dmemcg_pool_get(*ret_limit_pool);

		}

		dmemcg_pool_put(pool);

		ret = -EAGAIN;

		goto err;

	}
@@ -719,6 +774,7 @@ static ssize_t dmemcg_limit_write(struct kernfs_open_file *of, 


		/* And commit */

		apply(pool, new_limit);

		dmemcg_pool_put(pool);



out_put:

		kref_put(&region->ref, dmemcg_free_region);