From: Jason Gunthorpe <jgg@xxxxxxxxxxxx> [ Upstream commit 8bdf9dd984c18375d1090ddeb1792511f619c5c1 ] 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@xxxxxxxx Signed-off-by: Michael Guralnik <michaelgur@xxxxxxxxxxxx> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- drivers/infiniband/core/rdma_core.c | 23 +---------------------- include/rdma/uverbs_types.h | 1 - 2 files changed, 1 insertion(+), 23 deletions(-) diff --git a/drivers/infiniband/core/rdma_core.c b/drivers/infiniband/core/rdma_core.c index c4118bcd51035..c2c9bd72b350f 100644 --- a/drivers/infiniband/core/rdma_core.c +++ b/drivers/infiniband/core/rdma_core.c @@ -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) @@ -753,20 +747,6 @@ 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); @@ -954,7 +934,6 @@ 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); diff --git a/include/rdma/uverbs_types.h b/include/rdma/uverbs_types.h index acb1bfa3cc99a..f70155cc73979 100644 --- a/include/rdma/uverbs_types.h +++ b/include/rdma/uverbs_types.h @@ -97,7 +97,6 @@ struct uverbs_obj_type_class { int __must_check (*destroy_hw)(struct ib_uobject *uobj, enum rdma_remove_reason why); void (*remove_handle)(struct ib_uobject *uobj); - u8 needs_kfree_rcu; }; struct uverbs_obj_type { -- 2.20.1
