Messages in this thread | | | Date | Wed, 3 Jul 2019 21:36:06 +0200 | From | Greg KH <> | Subject | Re: [PATCH v4 OPT2] driver core: Fix use-after-free and double free on glue directory |
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On Wed, Jun 26, 2019 at 10:40:21PM +0800, 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_device_parent() > 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 can ensure the lookup of the glue > dir and creation of the child object(s) are done under a single instance > of gdp_mutex so we never see a stale "empty" but still poentially used > glue dir around. > > 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 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 | 108 +++++++++++++++++++++++++++++++++++++------- > 1 file changed, 92 insertions(+), 16 deletions(-) > > diff --git a/drivers/base/core.c b/drivers/base/core.c > index 4aeaa0c92bda..2251e391a352 100644 > --- a/drivers/base/core.c > +++ b/drivers/base/core.c > @@ -1739,8 +1739,23 @@ class_dir_create_and_add(struct class *class, struct kobject *parent_kobj) > > static DEFINE_MUTEX(gdp_mutex); > > -static struct kobject *get_device_parent(struct device *dev, > - struct device *parent) > +/** > + * __get_device_parent() - Get the parent device kobject. > + * @dev: Pointer to the device structure. > + * @parent: Pointer to the parent device structure. > + * @lock: When we live in a glue directory, should we hold the > + * gdp_mutex lock when this function returns? If @lock > + * is true, this function returns with the gdp_mutex > + * holed. Otherwise it will not.
Ugh, if you are trying to get me to hate one version of these patches, this is how you do it :)
A function should not "sometimes takes a lock, sometimes does not, depending on a parameter passed into it" That way lies madness...
> + * > + * Note: Only when we live in a glue directory and @lock is > + * true, the function will return with the gdp_mutex holed. > + * In this case, The caller is responsible for releasing the > + * gdp_mutex lock. > + */ > +static struct kobject *__get_device_parent(struct device *dev, > + struct device *parent, > + bool lock) > { > if (dev->class) { > struct kobject *kobj = NULL; > @@ -1778,16 +1793,32 @@ static struct kobject *get_device_parent(struct device *dev, > break; > } > spin_unlock(&dev->class->p->glue_dirs.list_lock); > - if (kobj) { > - mutex_unlock(&gdp_mutex); > - return kobj; > - } > > - /* or create a new class-directory at the parent device */ > - k = class_dir_create_and_add(dev->class, parent_kobj); > - /* do not emit an uevent for this simple "glue" directory */ > - mutex_unlock(&gdp_mutex); > - return k; > + /**
Note, in the future, you don't need to use /** for comments in a function, those are only for kernel doc markers for a _global_ function that gets pulled into the larger documentation documents. So even __get_device_parent() here does not need this.
Anyway, this is a mess.
Ugh I hate glue dirs...
greg k-h
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