Messages in this thread | | | Date | Tue, 30 Jul 2019 18:46:31 +0200 | From | Greg KH <> | Subject | Re: [PATCH v7] driver core: Fix use-after-free and double free on glue directory |
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On Sat, Jul 27, 2019 at 11:21:22AM +0800, Muchun Song wrote: > 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> > --- > > Change in v7: > 1. Update commit message. > Change in v6: > 1. Remove hardcoding "1 " > 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.
Now queued up, thanks for sticking with this.
greg k-h
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