From 091a0800664201c1719b2aa1bcd965f9578ee13e Mon Sep 17 00:00:00 2001 From: Muchun Song Date: Sun, 28 Apr 2019 23:31:06 +0800 Subject: [PATCH] driver core: Fix use-after-free and double free on glue directory 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 we should not call kobject_del() on path2 when the reference count of glue_dir is greater than 1. So we add a conditional statement to fix it. 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 --- drivers/base/core.c | 44 ++++++++++++++++++++++++++++++++++++-------- 1 file changed, 36 insertions(+), 8 deletions(-) diff --git a/drivers/base/core.c b/drivers/base/core.c index 4aeaa0c92bda..5112755c43fa 100644 --- a/drivers/base/core.c +++ b/drivers/base/core.c @@ -1739,8 +1739,9 @@ 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) +static struct kobject *__get_device_parent(struct device *dev, + struct device *parent, + bool lock) { if (dev->class) { struct kobject *kobj = NULL; @@ -1779,14 +1780,16 @@ static struct kobject *get_device_parent(struct device *dev, } spin_unlock(&dev->class->p->glue_dirs.list_lock); if (kobj) { - mutex_unlock(&gdp_mutex); + if (!lock) + 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); + if (!lock) + mutex_unlock(&gdp_mutex); return k; } @@ -1799,6 +1802,19 @@ static struct kobject *get_device_parent(struct device *dev, return NULL; } +static inline struct kobject *get_device_parent(struct device *dev, + struct device *parent) +{ + return __get_device_parent(dev, parent, false); +} + +static inline struct kobject * +get_device_parent_locked_if_glue_dir(struct device *dev, + struct device *parent) +{ + return __get_device_parent(dev, parent, true); +} + static inline bool live_in_glue_dir(struct kobject *kobj, struct device *dev) { @@ -1831,6 +1847,16 @@ static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir) mutex_unlock(&gdp_mutex); } +static inline void unlock_if_glue_dir(struct device *dev, + struct kobject *glue_dir) +{ + /* see if we live in a "glue" directory */ + if (!live_in_glue_dir(glue_dir, dev)) + return; + + mutex_unlock(&gdp_mutex); +} + static int device_add_class_symlinks(struct device *dev) { struct device_node *of_node = dev_of_node(dev); @@ -2040,7 +2066,7 @@ int device_add(struct device *dev) pr_debug("device: '%s': %s\n", dev_name(dev), __func__); parent = get_device(dev->parent); - kobj = get_device_parent(dev, parent); + kobj = get_device_parent_locked_if_glue_dir(dev, parent); if (IS_ERR(kobj)) { error = PTR_ERR(kobj); goto parent_error; @@ -2055,10 +2081,12 @@ int device_add(struct device *dev) /* first, register with generic layer. */ /* we require the name to be set before, and pass NULL */ error = kobject_add(&dev->kobj, dev->kobj.parent, NULL); - if (error) { - glue_dir = get_glue_dir(dev); + + glue_dir = get_glue_dir(dev); + unlock_if_glue_dir(dev, glue_dir); + + if (error) goto Error; - } /* notify platform of device entry */ error = device_platform_notify(dev, KOBJ_ADD); -- 2.17.1