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Subject[PATCH 2/6] Driver core: Fix memory leak on bus_register error path
Date
There is a subtle memory leak in driver core error path.
Consider the simplified view of bus_register (drivers/base/bus.c):

priv = kzalloc...
kobject_set_name(&priv->subsys.kobj,...) <== allocate in priv->subsys.kobj.name
if kset_register(&priv->subsys) FAILS:
(1) -- need to free name string here!
goto out
else
keep going, assume we fail later...

err_path_after_kset_register:
kset_unregister(&priv->subsys) <== calls kobject_put(&priv->subsys->kobj),
which is the last reference, which leads
to kobject_cleanup, which frees the name
field BUT DOES NOT SET IT TO NULL
out:
(2) Other place we could free name
kfree(bus->p) // bus->p = priv
...

Thus, we cannot insert the free'ing of name on the error path (2) since it will
be indeterminite if we need to free the name string or not. kset_register cannot (and
should not) free the name string if it fails since the caller may have other ideas,
leaving only (1) as a viable location to free the name string.

A walk-through of the failure path that will trigger this leak:

bus_register(struct bus_type *bus) {
...
priv = kzalloc...
kobject_set_name(&priv->subsys.kobj,... {
kobject_set_name_vargs(kobj,... {
kobj->name = kvasprintf... <== ALLOCATE INTO &priv->subsys.kobj.name

priv->subsys.kobj.kset = bus_kset
priv->subsys.kobj.ktype = &bus_ktype

retval = kset_register(&priv->subsys)...
if (retval) YES
goto out;

...
out:
kfree(bus->p);
bus->p = NULL;
return retval;
}

kset_register(struct kset *k) { // k = &priv->subsys
kset_init(k) {
kobject_init_internal(&k->kobj) {
kref_init(&kobj->kref) {
kref->refcount = 1

err = kobject_add_internal(&k->kobj)...
if (err) YES
return err;
...
}

kobject_add_internal(struct kobject *kobj) { // kobj = &priv->subsys.kobj
...
if (kobj->kset) YES {
kobj_kset_join(kobj) {
kset_get(kobj->kset) <== bus_kset
...
error = create_dir(kobj);
if (error) YES {
kobj_kset_leave(kobj) {
kset_put(kobj->kset) <== bus_kset
... (release parent and make KERN_ERR noise)
}
return error
}

Signed-off-by: Patrick Pannuto <ppannuto@codeaurora.org>
---
drivers/base/bus.c | 4 +++-
1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index eb1b7fa..fea1774 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -900,8 +900,10 @@ int bus_register(struct bus_type *bus)
priv->drivers_autoprobe = 1;

retval = kset_register(&priv->subsys);
- if (retval)
+ if (retval) {
+ kfree(priv->subsys.kobj.name);
goto out;
+ }

retval = bus_create_file(bus, &bus_attr_uevent);
if (retval)
--
1.7.2


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