[PATCHv3] mm/slab: fix race with dereferencing NULL ptr in alloc_calls_show
From: Dmitry Safonov
Date: Wed Feb 03 2016 - 02:53:00 EST
memcg_destroy_kmem_caches shutdowns in the first place kmem_caches under
slab_mutex which involves freeing NUMA node structures for kmem_cache
and only then under release_caches removes corresponding sysfs files for
these caches. Which may lead to dereferencing NULL ptr on read.
Lets remove sysfs files right there.
Fixes the following panic:
[43963.463055] BUG: unable to handle kernel
[43963.463090] NULL pointer dereference at 0000000000000020
[43963.463146] IP: [<ffffffff811c6959>] list_locations+0x169/0x4e0
[43963.463185] PGD 257304067 PUD 438456067 PMD 0
[43963.463220] Oops: 0000 [#1] SMP
[43963.463850] CPU: 3 PID: 973074 Comm: cat ve: 0 Not tainted 3.10.0-229.7.2.ovz.9.30-00007-japdoll-dirty #2 9.30
[43963.463913] Hardware name: DEPO Computers To Be Filled By O.E.M./H67DE3, BIOS L1.60c 07/14/2011
[43963.463976] task: ffff88042a5dc5b0 ti: ffff88037f8d8000 task.ti: ffff88037f8d8000
[43963.464036] RIP: 0010:[<ffffffff811c6959>] [<ffffffff811c6959>] list_locations+0x169/0x4e0
[43963.464725] Call Trace:
[43963.464756] [<ffffffff811c6d1d>] alloc_calls_show+0x1d/0x30
[43963.464793] [<ffffffff811c15ab>] slab_attr_show+0x1b/0x30
[43963.464829] [<ffffffff8125d27a>] sysfs_read_file+0x9a/0x1a0
[43963.464865] [<ffffffff811e3c6c>] vfs_read+0x9c/0x170
[43963.464900] [<ffffffff811e4798>] SyS_read+0x58/0xb0
[43963.464936] [<ffffffff81612d49>] system_call_fastpath+0x16/0x1b
[43963.464970] Code: 5e 07 12 00 b9 00 04 00 00 3d 00 04 00 00 0f 4f c1 3d 00 04 00 00 89 45 b0 0f 84 c3 00 00 00 48 63 45 b0 49 8b 9c c4 f8 00 00 00 <48> 8b 43 20 48 85 c0 74 b6 48 89 df e8 46 37 44 00 48 8b 53 10
[43963.465119] RIP [<ffffffff811c6959>] list_locations+0x169/0x4e0
[43963.465155] RSP <ffff88037f8dbe28>
[43963.465185] CR2: 0000000000000020
Cc: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Signed-off-by: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
---
v2: Down with SLAB_SUPPORTS_SYSFS thing.
v3: Moved sysfs_slab_remove inside shutdown_cache
include/linux/slub_def.h | 10 ----------
mm/slab.h | 8 ++++++++
mm/slab_common.c | 10 ++++------
mm/slub.c | 6 ------
4 files changed, 12 insertions(+), 22 deletions(-)
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index b7e57927..43634cd 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -101,16 +101,6 @@ struct kmem_cache {
struct kmem_cache_node *node[MAX_NUMNODES];
};
-#ifdef CONFIG_SYSFS
-#define SLAB_SUPPORTS_SYSFS
-void sysfs_slab_remove(struct kmem_cache *);
-#else
-static inline void sysfs_slab_remove(struct kmem_cache *s)
-{
-}
-#endif
-
-
/**
* virt_to_obj - returns address of the beginning of object.
* @s: object's kmem_cache
diff --git a/mm/slab.h b/mm/slab.h
index 834ad24..2983ab2 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -367,6 +367,14 @@ static inline struct kmem_cache_node *get_node(struct kmem_cache *s, int node)
#endif
+#if defined(CONFIG_SLUB) && defined(CONFIG_SYSFS)
+void sysfs_slab_remove(struct kmem_cache *);
+#else
+static inline void sysfs_slab_remove(struct kmem_cache *s)
+{
+}
+#endif
+
void *slab_start(struct seq_file *m, loff_t *pos);
void *slab_next(struct seq_file *m, void *p, loff_t *pos);
void slab_stop(struct seq_file *m, void *p);
diff --git a/mm/slab_common.c b/mm/slab_common.c
index b50aef0..2bfc0b1 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -451,6 +451,8 @@ EXPORT_SYMBOL(kmem_cache_create);
static int shutdown_cache(struct kmem_cache *s,
struct list_head *release, bool *need_rcu_barrier)
{
+ sysfs_slab_remove(s);
+
if (__kmem_cache_shutdown(s) != 0)
return -EBUSY;
@@ -468,13 +470,8 @@ static void release_caches(struct list_head *release, bool need_rcu_barrier)
if (need_rcu_barrier)
rcu_barrier();
- list_for_each_entry_safe(s, s2, release, list) {
-#ifdef SLAB_SUPPORTS_SYSFS
- sysfs_slab_remove(s);
-#else
+ list_for_each_entry_safe(s, s2, release, list)
slab_kmem_cache_release(s);
-#endif
- }
}
#if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB)
@@ -614,6 +611,7 @@ void memcg_destroy_kmem_caches(struct mem_cgroup *memcg)
list_for_each_entry_safe(s, s2, &slab_caches, list) {
if (is_root_cache(s) || s->memcg_params.memcg != memcg)
continue;
+
/*
* The cgroup is about to be freed and therefore has no charges
* left. Hence, all its caches must be empty by now.
diff --git a/mm/slub.c b/mm/slub.c
index 2e1355a..b6a68b7 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5296,11 +5296,6 @@ static void memcg_propagate_slab_attrs(struct kmem_cache *s)
#endif
}
-static void kmem_cache_release(struct kobject *k)
-{
- slab_kmem_cache_release(to_slab(k));
-}
-
static const struct sysfs_ops slab_sysfs_ops = {
.show = slab_attr_show,
.store = slab_attr_store,
@@ -5308,7 +5303,6 @@ static const struct sysfs_ops slab_sysfs_ops = {
static struct kobj_type slab_ktype = {
.sysfs_ops = &slab_sysfs_ops,
- .release = kmem_cache_release,
};
static int uevent_filter(struct kset *kset, struct kobject *kobj)
--
2.7.0