[syzbot] linux-next boot error: WARNING: refcount bug in dvb_register_device

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 15f2f20ccbf2 Add linux-next specific files for 20221128
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=114a14ad880000
kernel config: https://syzkaller.appspot.com/x/.config?x=50be0d6c9da3be9d
dashboard link: https://syzkaller.appspot.com/bug?extid=fce48a3dd3368645bd6c
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0bcd04c8e812/disk-15f2f20c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/23f3cf3f818e/vmlinux-15f2f20c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9111cdf112e7/bzImage-15f2f20c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fce48a...@syzkaller.appspotmail.com

usbcore: registered new interface driver sonixj
usbcore: registered new interface driver spca500
usbcore: registered new interface driver spca501
usbcore: registered new interface driver spca505
usbcore: registered new interface driver spca506
usbcore: registered new interface driver spca508
usbcore: registered new interface driver spca561
usbcore: registered new interface driver spca1528
usbcore: registered new interface driver sq905
usbcore: registered new interface driver sq905c
usbcore: registered new interface driver sq930x
usbcore: registered new interface driver sunplus
usbcore: registered new interface driver stk014
usbcore: registered new interface driver stk1135
usbcore: registered new interface driver stv0680
usbcore: registered new interface driver t613
usbcore: registered new interface driver gspca_topro
usbcore: registered new interface driver touptek
usbcore: registered new interface driver tv8532
usbcore: registered new interface driver vc032x
usbcore: registered new interface driver vicam
usbcore: registered new interface driver xirlink-cit
usbcore: registered new interface driver gspca_zc3xx
usbcore: registered new interface driver ALi m5602
usbcore: registered new interface driver STV06xx
usbcore: registered new interface driver gspca_gl860
usbcore: registered new interface driver hackrf
usbcore: registered new interface driver msi2500
usbcore: registered new interface driver Philips webcam
usbcore: registered new interface driver uvcvideo
au0828: au0828 driver loaded
usbcore: registered new interface driver au0828
usbcore: registered new interface driver cx231xx
usbcore: registered new interface driver em28xx
em28xx: Registered (Em28xx v4l2 Extension) extension
em28xx: Registered (Em28xx Audio Extension) extension
em28xx: Registered (Em28xx dvb Extension) extension
em28xx: Registered (Em28xx Input Extension) extension
usbcore: registered new interface driver go7007
usbcore: registered new interface driver go7007-loader
usbcore: registered new interface driver hdpvr
usbcore: registered new interface driver pvrusb2
pvrusb2: V4L in-tree version:Hauppauge WinTV-PVR-USB2 MPEG2 Encoder/Tuner
pvrusb2: Debug mask is 31 (0x1f)
usbcore: registered new interface driver stk1160
usbcore: registered new interface driver usbtv
dvbdev: DVB: registering new adapter (dvb_vidtv_bridge)
i2c i2c-0: DVB: registering adapter 0 frontend 0 (Dummy demod for DVB-T/T2/C/S/S2)...
------------[ cut here ]------------
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
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
RIP: 0010:refcount_warn_saturate+0x17c/0x1f0 lib/refcount.c:25
Code: 0a 31 ff 89 de e8 64 54 75 fd 84 db 0f 85 2e ff ff ff e8 e7 57 75 fd 48 c7 c7 60 4c a6 8a c6 05 bf 49 51 0a 01 e8 5c 83 b4 05 <0f> 0b e9 0f ff ff ff e8 c8 57 75 fd 0f b6 1d a9 49 51 0a 31 ff 89
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
dvb_register_frontend+0x58f/0x8c0 drivers/media/dvb-core/dvb_frontend.c:3044
vidtv_bridge_dvb_init drivers/media/test-drivers/vidtv/vidtv_bridge.c:430 [inline]
vidtv_bridge_probe+0x450/0x9f0 drivers/media/test-drivers/vidtv/vidtv_bridge.c:502
platform_probe+0x100/0x1f0 drivers/base/platform.c:1400
call_driver_probe drivers/base/dd.c:560 [inline]
really_probe+0x249/0xb90 drivers/base/dd.c:639
__driver_probe_device+0x1df/0x4d0 drivers/base/dd.c:778
driver_probe_device+0x4c/0x1a0 drivers/base/dd.c:808
__driver_attach+0x271/0x570 drivers/base/dd.c:1194
bus_for_each_dev+0x14b/0x1d0 drivers/base/bus.c:301
bus_add_driver+0x4cd/0x640 drivers/base/bus.c:618
driver_register+0x224/0x3a0 drivers/base/driver.c:246
vidtv_bridge_init+0x3b/0x68 drivers/media/test-drivers/vidtv/vidtv_bridge.c:594
do_one_initcall+0x141/0x790 init/main.c:1306
do_initcall_level init/main.c:1379 [inline]
do_initcalls init/main.c:1395 [inline]
do_basic_setup init/main.c:1414 [inline]
kernel_init_freeable+0x6f9/0x782 init/main.c:1634
kernel_init+0x1e/0x1d0 init/main.c:1522
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308
</TASK>


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[Zhongjin Chen]

0fc044b2b5e2d ("media: dvbdev: adopts refcnt to avoid UAF")

@@ -479,6 +482,7 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
                return -ENOMEM;
        }

+       kref_init(&dvbdev->ref);
        memcpy(dvbdev, template, sizeof(struct dvb_device));
        dvbdev->type = type;
        dvbdev->id = id;
@@ -510,7 +514,7 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
 #endif

        dvbdev->minor = minor;
-       dvb_minors[minor] = dvbdev;
+       dvb_minors[minor] = dvb_device_get(dvbdev);
        up_write(&minor_rwsem);

        ret = dvb_register_media_device(dvbdev, type, minor, demux_sink_pads);

Here the memcpy template to dvbdev overrides ref to zero so following dvb_device_get triggers addition refconunt on 0.

Seems  dvbdev->ref should be 1 after register, so init ref and dvb_device_get together is wrong.

So maybe we should call kref_init after memcpy and then assign dvbdev pointer derectly here?

Best,

Chen

[Lin Horse]

#syz test: https://github.com/f0rm2l1n/linux-next-mine.git 7b5bb460defa107dd2e82f950fddb9ea6bdb5e39