Messages in this thread | | | Subject | Re: [PATCH v5] driver core: Fix use-after-free and double free on glue directory | From | Mukesh Ojha <> | Date | Wed, 24 Jul 2019 19:11:05 +0530 |
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On 7/18/2019 4:49 PM, Muchun Song wrote: > There is a race condition between removing glue directory and adding a new > device under the glue directory. It can be reproduced in following test: > > path 1: Add the child device under glue dir > device_add() > get_device_parent() > mutex_lock(&gdp_mutex); > .... > /*find parent from glue_dirs.list*/ > list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry) > if (k->parent == parent_kobj) { > kobj = kobject_get(k); > break; > } > .... > mutex_unlock(&gdp_mutex); > .... > .... > kobject_add() > kobject_add_internal() > create_dir() > sysfs_create_dir_ns() > if (kobj->parent) > parent = kobj->parent->sd; > .... > kernfs_create_dir_ns(parent) > kernfs_new_node() > kernfs_get(parent) > .... > /* link in */ > rc = kernfs_add_one(kn); > if (!rc) > return kn; > > kernfs_put(kn) > .... > repeat: > kmem_cache_free(kn) > kn = parent; > > if (kn) { > if (atomic_dec_and_test(&kn->count)) > goto repeat; > } > .... > > path2: Remove last child device under glue dir > device_del() > cleanup_glue_dir() > mutex_lock(&gdp_mutex); > if (!kobject_has_children(glue_dir)) > kobject_del(glue_dir); > kobject_put(glue_dir); > mutex_unlock(&gdp_mutex); > > Before path2 remove last child device under glue dir, If path1 add a new > device under glue dir, the glue_dir kobject reference count will be > increase to 2 via kobject_get(k) in get_device_parent(). And path1 has > been called kernfs_new_node(), but not call kernfs_get(parent). > Meanwhile, path2 call kobject_del(glue_dir) beacause 0 is returned by > kobject_has_children(). This result in glue_dir->sd is freed and it's > reference count will be 0. Then path1 call kernfs_get(parent) will trigger > a warning in kernfs_get()(WARN_ON(!atomic_read(&kn->count))) and increase > it's reference count to 1. Because glue_dir->sd is freed by path2, the next > call kernfs_add_one() by path1 will fail(This is also use-after-free) > and call atomic_dec_and_test() to decrease reference count. Because the > reference count is decremented to 0, it will also call kmem_cache_free() > to free glue_dir->sd again. This will result in double free. > > In order to avoid this happening, we also should make sure that kernfs_node > for glue_dir is released in path2 only when refcount for glue_dir kobj is > 1 to fix this race. > > The following calltrace is captured in kernel 4.14 with the following patch > applied: > > commit 726e41097920 ("drivers: core: Remove glue dirs from sysfs earlier") > > -------------------------------------------------------------------------- > [ 3.633703] WARNING: CPU: 4 PID: 513 at .../fs/kernfs/dir.c:494 > Here is WARN_ON(!atomic_read(&kn->count) in kernfs_get(). > .... > [ 3.633986] Call trace: > [ 3.633991] kernfs_create_dir_ns+0xa8/0xb0 > [ 3.633994] sysfs_create_dir_ns+0x54/0xe8 > [ 3.634001] kobject_add_internal+0x22c/0x3f0 > [ 3.634005] kobject_add+0xe4/0x118 > [ 3.634011] device_add+0x200/0x870 > [ 3.634017] _request_firmware+0x958/0xc38 > [ 3.634020] request_firmware_into_buf+0x4c/0x70 > .... > [ 3.634064] kernel BUG at .../mm/slub.c:294! > Here is BUG_ON(object == fp) in set_freepointer(). > .... > [ 3.634346] Call trace: > [ 3.634351] kmem_cache_free+0x504/0x6b8 > [ 3.634355] kernfs_put+0x14c/0x1d8 > [ 3.634359] kernfs_create_dir_ns+0x88/0xb0 > [ 3.634362] sysfs_create_dir_ns+0x54/0xe8 > [ 3.634366] kobject_add_internal+0x22c/0x3f0 > [ 3.634370] kobject_add+0xe4/0x118 > [ 3.634374] device_add+0x200/0x870 > [ 3.634378] _request_firmware+0x958/0xc38 > [ 3.634381] request_firmware_into_buf+0x4c/0x70 > -------------------------------------------------------------------------- > > Fixes: 726e41097920 ("drivers: core: Remove glue dirs from sysfs earlier") > > Signed-off-by: Muchun Song <smuchun@gmail.com> > --- > > Change in v5: > 1. Revert to the v1 fix. > 2. Add some comment to explain why we need do this in > cleanup_glue_dir(). > Change in v4: > 1. Add some kerneldoc comment. > 2. Remove unlock_if_glue_dir(). > 3. Rename get_device_parent_locked_if_glue_dir() to > get_device_parent_locked. > 4. Update commit message. > Change in v3: > Add change log. > Change in v2: > Fix device_move() also. > > drivers/base/core.c | 54 ++++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 53 insertions(+), 1 deletion(-) > > diff --git a/drivers/base/core.c b/drivers/base/core.c > index 4aeaa0c92bda..1a67ee325584 100644 > --- a/drivers/base/core.c > +++ b/drivers/base/core.c > @@ -1825,7 +1825,59 @@ static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir) > return; > > mutex_lock(&gdp_mutex); > - if (!kobject_has_children(glue_dir)) > + /** > + * There is a race condition between removing glue directory > + * and adding a new device under the glue directory. > + * > + * path 1: Add the child device under glue dir > + * device_add() > + * get_device_parent() > + * mutex_lock(&gdp_mutex); > + * .... > + * list_for_each_entry(k, &dev->class->p->glue_dirs.list, > + * entry) > + * if (k->parent == parent_kobj) { > + * kobj = kobject_get(k); > + * break; > + * } > + * .... > + * mutex_unlock(&gdp_mutex); > + * .... > + * .... > + * kobject_add() > + * kobject_add_internal() > + * create_dir() > + * .... > + * if (kobj->parent) > + * parent = kobj->parent->sd; > + * .... > + * kernfs_create_dir_ns(parent) > + * .... > + * > + * path2: Remove last child device under glue dir > + * device_del() > + * cleanup_glue_dir() > + * .... > + * mutex_lock(&gdp_mutex); > + * if (!kobject_has_children(glue_dir)) > + * kobject_del(glue_dir); > + * .... > + * mutex_unlock(&gdp_mutex); > + * > + * Before path2 remove last child device under glue dir, if path1 add > + * a new device under glue dir, the glue_dir kobject reference count > + * will be increase to 2 via kobject_get(k) in get_device_parent(). > + * And path1 has been called kernfs_create_dir_ns(). Meanwhile, > + * path2 call kobject_del(glue_dir) beacause 0 is returned by > + * kobject_has_children(). This result in glue_dir->sd is freed. > + * Then the path1 will see a stale "empty" but still potentially used > + * glue dir around. > + * > + * In order to avoid this happening, we also should make sure that > + * kernfs_node for glue_dir is released in path2 only when refcount > + * for glue_dir kobj is 1. > + */ > + if (!kobject_has_children(glue_dir) && kref_read(&glue_dir->kref) == 1) Instead of hardcoding "1 " , can't we check against zero Like Prateek sood did in his patch.https://lkml.org/lkml/2019/5/1/3
+ref = kref_read(&glue_dir->kref); +if (!kobject_has_children(glue_dir) && --ref)
We have seen many pattern of this issue which is coming from different driver e.g uinput as well in 4.14 kernel.(https://lkml.org/lkml/2019/4/10/146) The reason why it started coming after
726e41097920 ("drivers: core: Remove glue dirs from sysfs earlier")
Looks good to me
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
-Mukesh
> kobject_del(glue_dir); > kobject_put(glue_dir); > mutex_unlock(&gdp_mutex);
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