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Subject[PATCH AUTOSEL 5.4 295/459] RDMA/uverbs: Remove needs_kfree_rcu from uverbs_obj_type_class
Date
From: Jason Gunthorpe <jgg@mellanox.com>

[ 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@ziepe.ca
Signed-off-by: Michael Guralnik <michaelgur@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 ccf4d069c25c9..7dd9bd1e4d118 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)
@@ -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);

@@ -919,7 +899,6 @@ 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 d57a5ba00c743..0b0f5a5f392de 100644
--- a/include/rdma/uverbs_types.h
+++ b/include/rdma/uverbs_types.h
@@ -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 {
--
2.20.1
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