Hi Christian
You are right on that part of obj-staged is set to NULL in add_fence, So my following question will be why we kfree(obj->staged) in reserve_shared() if staged is always NULL in that point ?
Thanks /Monk
-----Original Message----- From: Christian König [mailto:ckoenig.leichtzumerken@gmail.com] Sent: 2018年2月28日 16:27 To: Liu, Monk Monk.Liu@amd.com; dri-devel@lists.freedesktop.org; linux-kernel@vger.kernel.org Subject: Re: [PATCH] dma-buf/reservation: shouldn't kfree staged when slot available
Am 28.02.2018 um 07:44 schrieb Monk Liu:
under below scenario the obj->fence would refer to a wild pointer:
1,call reservation_object_reserved_shared 2,call reservation_object_add_shared_fence 3,call reservation_object_reserved_shared 4,call reservation_object_add_shared_fence
in step 1, staged is allocated,
in step 2, code path will go reservation_object_add_shared_replace() and obj->fence would be assigned as staged (through RCU_INIT_POINTER)
in step 3, obj->staged will be freed(by simple kfree), which make obj->fence point to a wild pointer...
Well that explanation is still nonsense. See reservation_object_add_shared_fence:
obj->staged = NULL;
Among the first things reservation_object_add_shared_fence() does is it sets obj->staged to NULL.
So step 3 will not free anything and we never have a wild pointer.
Regards, Christian.
in step 4, code path will go reservation_object_add_shared_inplace() and inside it the @fobj (which equals to @obj->staged, set by above steps) is already a wild pointer
should remov the kfree on staged in reservation_object_reserve_shared()
Change-Id: If7c01f1b4be3d3d8a81efa90216841f79ab1fc1c Signed-off-by: Monk Liu Monk.Liu@amd.com
drivers/dma-buf/reservation.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c index 375de41..b473ccc 100644 --- a/drivers/dma-buf/reservation.c +++ b/drivers/dma-buf/reservation.c @@ -74,12 +74,9 @@ int reservation_object_reserve_shared(struct reservation_object *obj) old = reservation_object_get_list(obj);
if (old && old->shared_max) {
if (old->shared_count < old->shared_max) {/* perform an in-place update */kfree(obj->staged);obj->staged = NULL;
if (old->shared_count < old->shared_max) return 0;
} else
else max = old->shared_max * 2;