linux-kernel - [PATCH] dma-buf/reservation: shouldn't kfree staged when slot available

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Message-ID: <1519800242-2442-1-git-send-email-Monk.Liu@amd.com>
Date:   Wed, 28 Feb 2018 14:44:02 +0800
From:   Monk Liu <Monk.Liu@....com>
To:     <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
CC:     Monk Liu <Monk.Liu@....com>
Subject: [PATCH] dma-buf/reservation: shouldn't kfree staged when slot available

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...

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@....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;
 	} else
 		max = 4;
-- 
2.7.4