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* [RFC PATCH] mm: memcontrol: fix use after free in mem_cgroup_iter()
@ 2019-07-25 14:27 miles.chen
  2019-07-25 19:21 ` Johannes Weiner
  0 siblings, 1 reply; 2+ messages in thread
From: miles.chen @ 2019-07-25 14:27 UTC (permalink / raw)
  To: Johannes Weiner, Michal Hocko, Vladimir Davydov
  Cc: cgroups, linux-mm, linux-kernel, wsd_upstream, linux-mediatek,
	Miles Chen

From: Miles Chen <miles.chen@mediatek.com>

This RFC patch is sent to report an use after free in mem_cgroup_iter()
after merging commit: be2657752e9e "mm: memcg: fix use after free in
mem_cgroup_iter()".

I work with android kernel tree (4.9 & 4.14), and the commit:
be2657752e9e "mm: memcg: fix use after free in mem_cgroup_iter()" has
been merged to the trees. However, I can still observe use after free
issues addressed in the commit be2657752e9e.
(on low-end devices, a few times this month)

backtrace:
	css_tryget <- crash here
	mem_cgroup_iter
	shrink_node
	shrink_zones
	do_try_to_free_pages
	try_to_free_pages
	__perform_reclaim
	__alloc_pages_direct_reclaim
	__alloc_pages_slowpath
	__alloc_pages_nodemask

To debug, I poisoned mem_cgroup before freeing it:

static void __mem_cgroup_free(struct mem_cgroup *memcg)
	for_each_node(node)
	free_mem_cgroup_per_node_info(memcg, node);
	free_percpu(memcg->stat);
+       /* poison memcg before freeing it */
+       memset(memcg, 0x78, sizeof(struct mem_cgroup));
	kfree(memcg);
}

The coredump shows the position=0xdbbc2a00 is freed.

(gdb) p/x ((struct mem_cgroup_per_node *)0xe5009e00)->iter[8]
$13 = {position = 0xdbbc2a00, generation = 0x2efd}

0xdbbc2a00:     0xdbbc2e00      0x00000000      0xdbbc2800      0x00000100
0xdbbc2a10:     0x00000200      0x78787878      0x00026218      0x00000000
0xdbbc2a20:     0xdcad6000      0x00000001      0x78787800      0x00000000
0xdbbc2a30:     0x78780000      0x00000000      0x0068fb84      0x78787878
0xdbbc2a40:     0x78787878      0x78787878      0x78787878      0xe3fa5cc0
0xdbbc2a50:     0x78787878      0x78787878      0x00000000      0x00000000
0xdbbc2a60:     0x00000000      0x00000000      0x00000000      0x00000000
0xdbbc2a70:     0x00000000      0x00000000      0x00000000      0x00000000
0xdbbc2a80:     0x00000000      0x00000000      0x00000000      0x00000000
0xdbbc2a90:     0x00000001      0x00000000      0x00000000      0x00100000
0xdbbc2aa0:     0x00000001      0xdbbc2ac8      0x00000000      0x00000000
0xdbbc2ab0:     0x00000000      0x00000000      0x00000000      0x00000000
0xdbbc2ac0:     0x00000000      0x00000000      0xe5b02618      0x00001000
0xdbbc2ad0:     0x00000000      0x78787878      0x78787878      0x78787878
0xdbbc2ae0:     0x78787878      0x78787878      0x78787878      0x78787878
0xdbbc2af0:     0x78787878      0x78787878      0x78787878      0x78787878
0xdbbc2b00:     0x78787878      0x78787878      0x78787878      0x78787878
0xdbbc2b10:     0x78787878      0x78787878      0x78787878      0x78787878
0xdbbc2b20:     0x78787878      0x78787878      0x78787878      0x78787878
0xdbbc2b30:     0x78787878      0x78787878      0x78787878      0x78787878
0xdbbc2b40:     0x78787878      0x78787878      0x78787878      0x78787878
0xdbbc2b50:     0x78787878      0x78787878      0x78787878      0x78787878
0xdbbc2b60:     0x78787878      0x78787878      0x78787878      0x78787878
0xdbbc2b70:     0x78787878      0x78787878      0x78787878      0x78787878
0xdbbc2b80:     0x78787878      0x78787878      0x00000000      0x78787878
0xdbbc2b90:     0x78787878      0x78787878      0x78787878      0x78787878
0xdbbc2ba0:     0x78787878      0x78787878      0x78787878      0x78787878

In the reclaim path, try_to_free_pages() does not setup
sc.target_mem_cgroup and sc is passed to do_try_to_free_pages(), ...,
shrink_node().

In mem_cgroup_iter(), root is set to root_mem_cgroup because
sc->target_mem_cgroup is NULL.
It is possible to assign a memcg to root_mem_cgroup.nodeinfo.iter in
mem_cgroup_iter().

	try_to_free_pages
		struct scan_control sc = {...}, target_mem_cgroup is 0x0;
	do_try_to_free_pages
	shrink_zones
	shrink_node
		 mem_cgroup *root = sc->target_mem_cgroup;
		 memcg = mem_cgroup_iter(root, NULL, &reclaim);
	mem_cgroup_iter()
		if (!root)
			root = root_mem_cgroup;
		...

		css = css_next_descendant_pre(css, &root->css);
		memcg = mem_cgroup_from_css(css);
		cmpxchg(&iter->position, pos, memcg);

My device uses memcg non-hierarchical mode.
When we release a memcg: invalidate_reclaim_iterators() reaches only
dead_memcg and its parents. If non-hierarchical mode is used,
invalidate_reclaim_iterators() never reaches root_mem_cgroup.

static void invalidate_reclaim_iterators(struct mem_cgroup *dead_memcg)
{
	struct mem_cgroup *memcg = dead_memcg;

	for (; memcg; memcg = parent_mem_cgroup(memcg)
	...
}

So the use after free scenario looks like:

CPU1						CPU2

try_to_free_pages
do_try_to_free_pages
shrink_zones
shrink_node
mem_cgroup_iter()
    if (!root)
    	root = root_mem_cgroup;
    ...
    css = css_next_descendant_pre(css, &root->css);
    memcg = mem_cgroup_from_css(css);
    cmpxchg(&iter->position, pos, memcg);

					invalidate_reclaim_iterators(memcg);
					...
					__mem_cgroup_free()
						kfree(memcg);

try_to_free_pages
do_try_to_free_pages
shrink_zones
shrink_node
mem_cgroup_iter()
    if (!root)
    	root = root_mem_cgroup;
    ...
    mz = mem_cgroup_nodeinfo(root, reclaim->pgdat->node_id);
    iter = &mz->iter[reclaim->priority];
    pos = READ_ONCE(iter->position);
    css_tryget(&pos->css) <- use after free

To avoid this, we should also invalidate root_mem_cgroup.nodeinfo.iter in
invalidate_reclaim_iterators().

Signed-off-by: Miles Chen <miles.chen@mediatek.com>
---
 mm/memcontrol.c | 33 +++++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index cdbb7a84cb6e..578b02982c9a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1130,26 +1130,39 @@ void mem_cgroup_iter_break(struct mem_cgroup *root,
 		css_put(&prev->css);
 }
 
-static void invalidate_reclaim_iterators(struct mem_cgroup *dead_memcg)
+static void __invalidate_reclaim_iterators(struct mem_cgroup *from,
+					struct mem_cgroup *dead_memcg)
 {
-	struct mem_cgroup *memcg = dead_memcg;
 	struct mem_cgroup_reclaim_iter *iter;
 	struct mem_cgroup_per_node *mz;
 	int nid;
 	int i;
 
-	for (; memcg; memcg = parent_mem_cgroup(memcg)) {
-		for_each_node(nid) {
-			mz = mem_cgroup_nodeinfo(memcg, nid);
-			for (i = 0; i <= DEF_PRIORITY; i++) {
-				iter = &mz->iter[i];
-				cmpxchg(&iter->position,
-					dead_memcg, NULL);
-			}
+	for_each_node(nid) {
+		mz = mem_cgroup_nodeinfo(from, nid);
+		for (i = 0; i <= DEF_PRIORITY; i++) {
+			iter = &mz->iter[i];
+			cmpxchg(&iter->position,
+				dead_memcg, NULL);
 		}
 	}
 }
 
+static void invalidate_reclaim_iterators(struct mem_cgroup *dead_memcg)
+{
+	struct mem_cgroup *memcg = dead_memcg;
+	int invalid_root = 0;
+
+	for (; memcg; memcg = parent_mem_cgroup(memcg)) {
+		__invalidate_reclaim_iterators(memcg, dead_memcg);
+		if (memcg == root_mem_cgroup)
+			invalid_root = 1;
+	}
+
+	if (!invalid_root)
+		__invalidate_reclaim_iterators(root_mem_cgroup, dead_memcg);
+}
+
 /**
  * mem_cgroup_scan_tasks - iterate over tasks of a memory cgroup hierarchy
  * @memcg: hierarchy root
-- 
2.18.0


^ permalink raw reply related	[flat|nested] 2+ messages in thread
* Re: [RFC PATCH] mm: memcontrol: fix use after free in mem_cgroup_iter()
  2019-07-25 14:27 [RFC PATCH] mm: memcontrol: fix use after free in mem_cgroup_iter() miles.chen
@ 2019-07-25 19:21 ` Johannes Weiner
  0 siblings, 0 replies; 2+ messages in thread
From: Johannes Weiner @ 2019-07-25 19:21 UTC (permalink / raw)
  To: miles.chen
  Cc: Michal Hocko, Vladimir Davydov, cgroups, linux-mm, linux-kernel,
	wsd_upstream, linux-mediatek

On Thu, Jul 25, 2019 at 10:27:03PM +0800, miles.chen@mediatek.com wrote:
> From: Miles Chen <miles.chen@mediatek.com>
> 
> This RFC patch is sent to report an use after free in mem_cgroup_iter()
> after merging commit: be2657752e9e "mm: memcg: fix use after free in
> mem_cgroup_iter()".
> 
> I work with android kernel tree (4.9 & 4.14), and the commit:
> be2657752e9e "mm: memcg: fix use after free in mem_cgroup_iter()" has
> been merged to the trees. However, I can still observe use after free
> issues addressed in the commit be2657752e9e.
> (on low-end devices, a few times this month)
> 
> backtrace:
> 	css_tryget <- crash here
> 	mem_cgroup_iter
> 	shrink_node
> 	shrink_zones
> 	do_try_to_free_pages
> 	try_to_free_pages
> 	__perform_reclaim
> 	__alloc_pages_direct_reclaim
> 	__alloc_pages_slowpath
> 	__alloc_pages_nodemask
> 
> To debug, I poisoned mem_cgroup before freeing it:
> 
> static void __mem_cgroup_free(struct mem_cgroup *memcg)
> 	for_each_node(node)
> 	free_mem_cgroup_per_node_info(memcg, node);
> 	free_percpu(memcg->stat);
> +       /* poison memcg before freeing it */
> +       memset(memcg, 0x78, sizeof(struct mem_cgroup));
> 	kfree(memcg);
> }
> 
> The coredump shows the position=0xdbbc2a00 is freed.
> 
> (gdb) p/x ((struct mem_cgroup_per_node *)0xe5009e00)->iter[8]
> $13 = {position = 0xdbbc2a00, generation = 0x2efd}
> 
> 0xdbbc2a00:     0xdbbc2e00      0x00000000      0xdbbc2800      0x00000100
> 0xdbbc2a10:     0x00000200      0x78787878      0x00026218      0x00000000
> 0xdbbc2a20:     0xdcad6000      0x00000001      0x78787800      0x00000000
> 0xdbbc2a30:     0x78780000      0x00000000      0x0068fb84      0x78787878
> 0xdbbc2a40:     0x78787878      0x78787878      0x78787878      0xe3fa5cc0
> 0xdbbc2a50:     0x78787878      0x78787878      0x00000000      0x00000000
> 0xdbbc2a60:     0x00000000      0x00000000      0x00000000      0x00000000
> 0xdbbc2a70:     0x00000000      0x00000000      0x00000000      0x00000000
> 0xdbbc2a80:     0x00000000      0x00000000      0x00000000      0x00000000
> 0xdbbc2a90:     0x00000001      0x00000000      0x00000000      0x00100000
> 0xdbbc2aa0:     0x00000001      0xdbbc2ac8      0x00000000      0x00000000
> 0xdbbc2ab0:     0x00000000      0x00000000      0x00000000      0x00000000
> 0xdbbc2ac0:     0x00000000      0x00000000      0xe5b02618      0x00001000
> 0xdbbc2ad0:     0x00000000      0x78787878      0x78787878      0x78787878
> 0xdbbc2ae0:     0x78787878      0x78787878      0x78787878      0x78787878
> 0xdbbc2af0:     0x78787878      0x78787878      0x78787878      0x78787878
> 0xdbbc2b00:     0x78787878      0x78787878      0x78787878      0x78787878
> 0xdbbc2b10:     0x78787878      0x78787878      0x78787878      0x78787878
> 0xdbbc2b20:     0x78787878      0x78787878      0x78787878      0x78787878
> 0xdbbc2b30:     0x78787878      0x78787878      0x78787878      0x78787878
> 0xdbbc2b40:     0x78787878      0x78787878      0x78787878      0x78787878
> 0xdbbc2b50:     0x78787878      0x78787878      0x78787878      0x78787878
> 0xdbbc2b60:     0x78787878      0x78787878      0x78787878      0x78787878
> 0xdbbc2b70:     0x78787878      0x78787878      0x78787878      0x78787878
> 0xdbbc2b80:     0x78787878      0x78787878      0x00000000      0x78787878
> 0xdbbc2b90:     0x78787878      0x78787878      0x78787878      0x78787878
> 0xdbbc2ba0:     0x78787878      0x78787878      0x78787878      0x78787878
> 
> In the reclaim path, try_to_free_pages() does not setup
> sc.target_mem_cgroup and sc is passed to do_try_to_free_pages(), ...,
> shrink_node().
> 
> In mem_cgroup_iter(), root is set to root_mem_cgroup because
> sc->target_mem_cgroup is NULL.
> It is possible to assign a memcg to root_mem_cgroup.nodeinfo.iter in
> mem_cgroup_iter().
> 
> 	try_to_free_pages
> 		struct scan_control sc = {...}, target_mem_cgroup is 0x0;
> 	do_try_to_free_pages
> 	shrink_zones
> 	shrink_node
> 		 mem_cgroup *root = sc->target_mem_cgroup;
> 		 memcg = mem_cgroup_iter(root, NULL, &reclaim);
> 	mem_cgroup_iter()
> 		if (!root)
> 			root = root_mem_cgroup;
> 		...
> 
> 		css = css_next_descendant_pre(css, &root->css);
> 		memcg = mem_cgroup_from_css(css);
> 		cmpxchg(&iter->position, pos, memcg);
> 
> My device uses memcg non-hierarchical mode.
> When we release a memcg: invalidate_reclaim_iterators() reaches only
> dead_memcg and its parents. If non-hierarchical mode is used,
> invalidate_reclaim_iterators() never reaches root_mem_cgroup.
> 
> static void invalidate_reclaim_iterators(struct mem_cgroup *dead_memcg)
> {
> 	struct mem_cgroup *memcg = dead_memcg;
> 
> 	for (; memcg; memcg = parent_mem_cgroup(memcg)
> 	...
> }
> 
> So the use after free scenario looks like:
> 
> CPU1						CPU2
> 
> try_to_free_pages
> do_try_to_free_pages
> shrink_zones
> shrink_node
> mem_cgroup_iter()
>     if (!root)
>     	root = root_mem_cgroup;
>     ...
>     css = css_next_descendant_pre(css, &root->css);
>     memcg = mem_cgroup_from_css(css);
>     cmpxchg(&iter->position, pos, memcg);
> 
> 					invalidate_reclaim_iterators(memcg);
> 					...
> 					__mem_cgroup_free()
> 						kfree(memcg);
> 
> try_to_free_pages
> do_try_to_free_pages
> shrink_zones
> shrink_node
> mem_cgroup_iter()
>     if (!root)
>     	root = root_mem_cgroup;
>     ...
>     mz = mem_cgroup_nodeinfo(root, reclaim->pgdat->node_id);
>     iter = &mz->iter[reclaim->priority];
>     pos = READ_ONCE(iter->position);
>     css_tryget(&pos->css) <- use after free
> 
> To avoid this, we should also invalidate root_mem_cgroup.nodeinfo.iter in
> invalidate_reclaim_iterators().
> 
> Signed-off-by: Miles Chen <miles.chen@mediatek.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

This looks good to me, but please add a comment that documents why you
need to handle root_mem_cgroup separately:

> +static void invalidate_reclaim_iterators(struct mem_cgroup *dead_memcg)
> +{
> +	struct mem_cgroup *memcg = dead_memcg;
> +	int invalid_root = 0;
> +
> +	for (; memcg; memcg = parent_mem_cgroup(memcg)) {
> +		__invalidate_reclaim_iterators(memcg, dead_memcg);
> +		if (memcg == root_mem_cgroup)
> +			invalid_root = 1;
> +	}
> +
> +	if (!invalid_root)
> +		__invalidate_reclaim_iterators(root_mem_cgroup, dead_memcg);

^ This block should have a comment that mentions that non-hierarchy
mode in cgroup1 means that parent_mem_cgroup doesn't walk all the way
up to the cgroup root.

^ permalink raw reply	[flat|nested] 2+ messages in thread
end of thread, other threads:[~2019-07-25 19:21 UTC | newest]

Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
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2019-07-25 14:27 [RFC PATCH] mm: memcontrol: fix use after free in mem_cgroup_iter() miles.chen
2019-07-25 19:21 ` Johannes Weiner

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