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Message-ID: <885c2912-029d-5c2e-8c2b-89bea2d763ac@codeaurora.org>
Date: Wed, 24 Jul 2019 19:53:36 +0530
From: Mukesh Ojha <mojha@...eaurora.org>
To: Muchun Song <smuchun@...il.com>, gregkh@...uxfoundation.org,
rafael@...nel.org
Cc: benh@...nel.crashing.org, prsood@...eaurora.org,
gkohli@...eaurora.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] driver core: Fix use-after-free and double free on
glue directory
On 7/24/2019 7:11 PM, Mukesh Ojha wrote:
>
> 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@...il.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)
>
I meant 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@...eaurora.org>
>
>
> -Mukesh
>
>
>> kobject_del(glue_dir);
>> kobject_put(glue_dir);
>> mutex_unlock(&gdp_mutex);
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