[PATCH 5.15 730/731] media: dvbdev: fix refcnt bug

Greg Kroah-Hartman
2022-12-28T16:05:20Z

From: Lin Ma <linma@zju.edu.cn>

commit 3a664569b71b0a52be5ffb9fb87cc4f83d29bd71 upstream.

Previous commit initialize the dvbdev->ref before the template copy,
which will overwrite the reference and cause refcnt bug.

refcount_t: addition on 0; use-after-free.
WARNING: CPU: 0 PID: 1 at lib/refcount.c:25 refcount_warn_saturate+0x17c/0x1f0 lib/refcount.c:25
Modules linked in:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.1.0-rc6-next-20221128-syzkaller #0
...
RIP: 0010:refcount_warn_saturate+0x17c/0x1f0 lib/refcount.c:25
RSP: 0000:ffffc900000678d0 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff88813ff58000 RSI: ffffffff81660e7c RDI: fffff5200000cf0c
RBP: ffff888022a45010 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000080000000 R11: 0000000000000000 R12: 0000000000000001
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000001
FS: 0000000000000000(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff88823ffff000 CR3: 000000000c48e000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__refcount_add include/linux/refcount.h:199 [inline]
__refcount_inc include/linux/refcount.h:250 [inline]
refcount_inc include/linux/refcount.h:267 [inline]
kref_get include/linux/kref.h:45 [inline]
dvb_device_get drivers/media/dvb-core/dvbdev.c:585 [inline]
dvb_register_device+0xe83/0x16e0 drivers/media/dvb-core/dvbdev.c:517
...

Just place the kref_init at correct position.

Reported-by: syzbot+fce48a3dd3368645bd6c@syzkaller.appspotmail.com
Fixes: 0fc044b2b5e2 ("media: dvbdev: adopts refcnt to avoid UAF")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/media/dvb-core/dvbdev.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/media/dvb-core/dvbdev.c
+++ b/drivers/media/dvb-core/dvbdev.c
@@ -490,8 +490,8 @@ int dvb_register_device(struct dvb_adapt
return -ENOMEM;
}

- kref_init(&dvbdev->ref);
memcpy(dvbdev, template, sizeof(struct dvb_device));
+ kref_init(&dvbdev->ref);
dvbdev->type = type;
dvbdev->id = id;
dvbdev->adapter = adap;