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RDMA/uverbs: Remove needs_kfree_rcu from uverbs_obj_type_class 

After device disassociation the uapi_objects are destroyed and freed,
however it is still possible that core code can be holding a kref on the
uobject. When it finally goes to uverbs_uobject_free() via the kref_put()
it can trigger a use-after-free on the uapi_object.

Since needs_kfree_rcu is a micro optimization that only benefits file
uobjects, just get rid of it. There is no harm in using kfree_rcu even if
it isn't required, and the number of involved objects is small.

Link: https://lore.kernel.org/r/20200113143306.GA28717@ziepe.ca
Signed-off-by: Michael Guralnik <michaelgur@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
This commit is contained in:
Jason Gunthorpe 2020-01-13 14:33:10 +00:00
parent 3f59b6c3e6
commit 8bdf9dd984
2 changed files with 1 additions and 23 deletions
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23
drivers/infiniband/core/rdma_core.c
View File

@ -49,13 +49,7 @@ void uverbs_uobject_get(struct ib_uobject *uobject)
static void uverbs_uobject_free(struct kref *ref)
{
struct ib_uobject *uobj =
container_of(ref, struct ib_uobject, ref);
if (uobj->uapi_object->type_class->needs_kfree_rcu)
kfree_rcu(uobj, rcu);
else
kfree(uobj);
kfree_rcu(container_of(ref, struct ib_uobject, ref), rcu);
}
void uverbs_uobject_put(struct ib_uobject *uobject)
@ -744,20 +738,6 @@ const struct uverbs_obj_type_class uverbs_idr_class = {
.lookup_put = lookup_put_idr_uobject,
.destroy_hw = destroy_hw_idr_uobject,
.remove_handle = remove_handle_idr_uobject,
/*
* When we destroy an object, we first just lock it for WRITE and
* actually DESTROY it in the finalize stage. So, the problematic
* scenario is when we just started the finalize stage of the
* destruction (nothing was executed yet). Now, the other thread
* fetched the object for READ access, but it didn't lock it yet.
* The DESTROY thread continues and starts destroying the object.
* When the other thread continue - without the RCU, it would
* access freed memory. However, the rcu_read_lock delays the free
* until the rcu_read_lock of the READ operation quits. Since the
* exclusive lock of the object is still taken by the DESTROY flow, the
* READ operation will get -EBUSY and it'll just bail out.
*/
.needs_kfree_rcu = true,
};
EXPORT_SYMBOL(uverbs_idr_class);
@ -920,7 +900,6 @@ const struct uverbs_obj_type_class uverbs_fd_class = {
.lookup_put = lookup_put_fd_uobject,
.destroy_hw = destroy_hw_fd_uobject,
.remove_handle = remove_handle_fd_uobject,
.needs_kfree_rcu = false,
};
EXPORT_SYMBOL(uverbs_fd_class);

1
include/rdma/uverbs_types.h
View File

@ -98,7 +98,6 @@ struct uverbs_obj_type_class {
enum rdma_remove_reason why,
struct uverbs_attr_bundle *attrs);
void (*remove_handle)(struct ib_uobject *uobj);
u8 needs_kfree_rcu;
};
struct uverbs_obj_type {