Messages in this thread | | | Subject | Re: [PATCH v5] driver core: Fix use-after-free and double free on glue directory | From | Mukesh Ojha <> | Date | Wed, 24 Jul 2019 19:53:36 +0530 |
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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@gmail.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@codeaurora.org> > > > -Mukesh > > >> kobject_del(glue_dir); >> kobject_put(glue_dir); >> mutex_unlock(&gdp_mutex);
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