linux-kernel - [PATCH] [media] v4l2-core: fix use-after-free error

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Date:   Wed, 10 Apr 2019 19:58:28 +0530
From:   Sumit Gupta <sumitg@...dia.com>
To:     <mchehab@...nel.org>, <hverkuil-cisco@...all.nl>,
        <sakari.ailus@...ux.intel.com>, <paul.kocialkowski@...tlin.com>,
        <tfiga@...omium.org>, <keiichiw@...omium.org>, <sumitg@...dia.com>
CC:     <linux-media@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] [media] v4l2-core: fix use-after-free error

From: sumitg <sumitg@...dia.com>

Fixing use-after-free within __v4l2_ctrl_handler_setup().
Memory is being freed with kfree(new_ref) for duplicate
control reference entry but cluster is still referring
to the duplicate entry. Change done to point cluster to
original reference instead of duplicate which is freed.

 ==================================================================
 BUG: KASAN: use-after-free in __v4l2_ctrl_handler_setup+0x388/0x428
 Read of size 8 at addr ffffffc324e78618 by task systemd-udevd/312

 Allocated by task 312:

 Freed by task 312:

 The buggy address belongs to the object at ffffffc324e78600
  which belongs to the cache kmalloc-64 of size 64
 The buggy address is located 24 bytes inside of
  64-byte region [ffffffc324e78600, ffffffc324e78640)
 The buggy address belongs to the page:
 page:ffffffbf0c939e00 count:1 mapcount:0 mapping:
					(null) index:0xffffffc324e78f80
 flags: 0x4000000000000100(slab)
 raw: 4000000000000100 0000000000000000 ffffffc324e78f80 000000018020001a
 raw: 0000000000000000 0000000100000001 ffffffc37040fb80 0000000000000000
 page dumped because: kasan: bad access detected

 Memory state around the buggy address:
  ffffffc324e78500: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
  ffffffc324e78580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 >ffffffc324e78600: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                             ^
  ffffffc324e78680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
  ffffffc324e78700: 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc
 ==================================================================

Signed-off-by: sumitg <sumitg@...dia.com>
---
 drivers/media/v4l2-core/v4l2-ctrls.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
index 5e3806f..e971bab 100644
--- a/drivers/media/v4l2-core/v4l2-ctrls.c
+++ b/drivers/media/v4l2-core/v4l2-ctrls.c
@@ -2182,6 +2182,7 @@ static int handler_new_ref(struct v4l2_ctrl_handler *hdl,
 			continue;
 		/* Don't add duplicates */
 		if (ref->ctrl->id == id) {
+			ctrl->cluster = &ref->ctrl;
 			kfree(new_ref);
 			goto unlock;
 		}
-- 
2.7.4