Re: [PATCH AUTOSEL 4.19 31/68] driver core: Fix use-after-free and double free on glue directory

Greg Kroah-Hartman
2019-08-14T07:36:37Z

On Tue, Aug 13, 2019 at 10:15:09PM -0400, Sasha Levin wrote:
> From: Muchun Song <smuchun@gmail.com>
>
> [ Upstream commit ac43432cb1f5c2950408534987e57c2071e24d8f ]
>
> There is a race condition between removing glue directory and adding a new
> device under the glue dir. It can be reproduced in following test:
>
> CPU1: CPU2:
>
> device_add()
> get_device_parent()
> class_dir_create_and_add()
> kobject_add_internal()
> create_dir() // create glue_dir
>
> device_add()
> get_device_parent()
> kobject_get() // get glue_dir
>
> device_del()
> cleanup_glue_dir()
> kobject_del(glue_dir)
>
> kobject_add()
> kobject_add_internal()
> create_dir() // in glue_dir
> sysfs_create_dir_ns()
> kernfs_create_dir_ns(sd)
>
> sysfs_remove_dir() // glue_dir->sd=NULL
> sysfs_put() // free glue_dir->sd
>
> // sd is freed
> kernfs_new_node(sd)
> kernfs_get(glue_dir)
> kernfs_add_one()
> kernfs_put()
>
> Before CPU1 remove last child device under glue dir, if CPU2 add a new
> device under glue dir, the glue_dir kobject reference count will be
> increase to 2 via kobject_get() in get_device_parent(). And CPU2 has
> been called kernfs_create_dir_ns(), but not call kernfs_new_node().
> Meanwhile, CPU1 call sysfs_remove_dir() and sysfs_put(). This result in
> glue_dir->sd is freed and it's reference count will be 0. Then CPU2 call
> kernfs_get(glue_dir) will trigger a warning in kernfs_get() and increase
> it's reference count to 1. Because glue_dir->sd is freed by CPU1, the next
> call kernfs_add_one() by CPU2 will fail(This is also use-after-free)
> and call kernfs_put() to decrease reference count. Because the reference
> count is decremented to 0, it will also call kmem_cache_free() to free
> the 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 CPU1 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>
> Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
> Signed-off-by: Prateek Sood <prsood@codeaurora.org>
> Link: https://lore.kernel.org/r/20190727032122.24639-1-smuchun@gmail.com
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> drivers/base/core.c | 53 ++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 52 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index e1a8d5c06f65e..fcda6313e7def 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -1648,12 +1648,63 @@ static inline struct kobject *get_glue_dir(struct device *dev)
> */
> static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir)
> {
> + unsigned int ref;
> +
> /* see if we live in a "glue" directory */
> if (!live_in_glue_dir(glue_dir, dev))
> 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.
> + *
> + * CPU1: CPU2:
> + *
> + * device_add()
> + * get_device_parent()
> + * class_dir_create_and_add()
> + * kobject_add_internal()
> + * create_dir() // create glue_dir
> + *
> + * device_add()
> + * get_device_parent()
> + * kobject_get() // get glue_dir
> + *
> + * device_del()
> + * cleanup_glue_dir()
> + * kobject_del(glue_dir)
> + *
> + * kobject_add()
> + * kobject_add_internal()
> + * create_dir() // in glue_dir
> + * sysfs_create_dir_ns()
> + * kernfs_create_dir_ns(sd)
> + *
> + * sysfs_remove_dir() // glue_dir->sd=NULL
> + * sysfs_put() // free glue_dir->sd
> + *
> + * // sd is freed
> + * kernfs_new_node(sd)
> + * kernfs_get(glue_dir)
> + * kernfs_add_one()
> + * kernfs_put()
> + *
> + * Before CPU1 remove last child device under glue dir, if CPU2 add
> + * a new device under glue dir, the glue_dir kobject reference count
> + * will be increase to 2 in kobject_get(k). And CPU2 has been called
> + * kernfs_create_dir_ns(). Meanwhile, CPU1 call sysfs_remove_dir()
> + * and sysfs_put(). This result in glue_dir->sd is freed.
> + *
> + * Then the CPU2 will see a stale "empty" but still potentially used
> + * glue dir around in kernfs_new_node().
> + *
> + * In order to avoid this happening, we also should make sure that
> + * kernfs_node for glue_dir is released in CPU1 only when refcount
> + * for glue_dir kobj is 1.
> + */
> + ref = kref_read(&glue_dir->kref);
> + if (!kobject_has_children(glue_dir) && !--ref)
> kobject_del(glue_dir);
> kobject_put(glue_dir);
> mutex_unlock(&gdp_mutex);

Same here, please drop for now.

thanks,

greg k-h