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Subject[PATCH 3.16 186/202] media: em28xx: Fix use-after-free when disconnecting
3.16.66-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Matthias Schwarzott <zzam@gentoo.org>

commit 910b0797fa9e8af09c44a3fa36cb310ba7a7218d upstream.

Fix bug by moving the i2c_unregister_device calls after deregistration
of dvb frontend.

The new style i2c drivers already destroys the frontend object at
i2c_unregister_device time.
When the dvb frontend is unregistered afterwards it leads to this oops:

[ 6058.866459] BUG: unable to handle kernel NULL pointer dereference at 00000000000001f8
[ 6058.866578] IP: dvb_frontend_stop+0x30/0xd0 [dvb_core]
[ 6058.866644] PGD 0
[ 6058.866646] P4D 0

[ 6058.866726] Oops: 0000 [#1] SMP
[ 6058.866768] Modules linked in: rc_pinnacle_pctv_hd(O) em28xx_rc(O) si2157(O) si2168(O) em28xx_dvb(O) em28xx(O) si2165(O) a8293(O) tda10071(O) tea5767(O) tuner(O) cx23885(O) tda18271(O) videobuf2_dvb(O) videobuf2_dma_sg(O) m88ds3103(O) tveeprom(O) cx2341x(O) v4l2_common(O) dvb_core(O) rc_core(O) videobuf2_memops(O) videobuf2_v4l2(O) videobuf2_core(O) videodev(O) media(O) bluetooth ecdh_generic ums_realtek uas rtl8192cu rtl_usb rtl8192c_common rtlwifi usb_storage snd_hda_codec_realtek snd_hda_codec_hdmi snd_hda_codec_generic i2c_mux snd_hda_intel snd_hda_codec snd_hwdep x86_pkg_temp_thermal snd_hda_core kvm_intel kvm irqbypass [last unloaded: videobuf2_memops]
[ 6058.867497] CPU: 2 PID: 7349 Comm: kworker/2:0 Tainted: G W O 4.13.9-gentoo #1
[ 6058.867595] Hardware name: MEDION E2050 2391/H81H3-EM2, BIOS H81EM2W08.308 08/25/2014
[ 6058.867692] Workqueue: usb_hub_wq hub_event
[ 6058.867746] task: ffff88011a15e040 task.stack: ffffc90003074000
[ 6058.867825] RIP: 0010:dvb_frontend_stop+0x30/0xd0 [dvb_core]
[ 6058.867896] RSP: 0018:ffffc90003077b58 EFLAGS: 00010293
[ 6058.867964] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 000000010040001f
[ 6058.868056] RDX: ffff88011a15e040 RSI: ffffea000464e400 RDI: ffff88001cbe3028
[ 6058.868150] RBP: ffffc90003077b68 R08: ffff880119390380 R09: 000000010040001f
[ 6058.868241] R10: ffffc90003077b18 R11: 000000000001e200 R12: ffff88001cbe3028
[ 6058.868330] R13: ffff88001cbe68d0 R14: ffff8800cf734000 R15: ffff8800cf734098
[ 6058.868419] FS: 0000000000000000(0000) GS:ffff88011fb00000(0000) knlGS:0000000000000000
[ 6058.868511] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 6058.868578] CR2: 00000000000001f8 CR3: 00000001113c5000 CR4: 00000000001406e0
[ 6058.868662] Call Trace:
[ 6058.868705] dvb_unregister_frontend+0x2a/0x80 [dvb_core]
[ 6058.868774] em28xx_dvb_fini+0x132/0x220 [em28xx_dvb]
[ 6058.868840] em28xx_close_extension+0x34/0x90 [em28xx]
[ 6058.868902] em28xx_usb_disconnect+0x4e/0x70 [em28xx]
[ 6058.868968] usb_unbind_interface+0x6d/0x260
[ 6058.869025] device_release_driver_internal+0x150/0x210
[ 6058.869094] device_release_driver+0xd/0x10
[ 6058.869150] bus_remove_device+0xe4/0x160
[ 6058.869204] device_del+0x1ce/0x2f0
[ 6058.869253] usb_disable_device+0x99/0x270
[ 6058.869306] usb_disconnect+0x8d/0x260
[ 6058.869359] hub_event+0x93d/0x1520
[ 6058.869408] ? dequeue_task_fair+0xae5/0xd20
[ 6058.869467] process_one_work+0x1d9/0x3e0
[ 6058.869522] worker_thread+0x43/0x3e0
[ 6058.869576] kthread+0x104/0x140
[ 6058.869602] ? trace_event_raw_event_workqueue_work+0x80/0x80
[ 6058.869640] ? kthread_create_on_node+0x40/0x40
[ 6058.869673] ret_from_fork+0x22/0x30
[ 6058.869698] Code: 54 49 89 fc 53 48 8b 9f 18 03 00 00 0f 1f 44 00 00 41 83 bc 24 04 05 00 00 02 74 0c 41 c7 84 24 04 05 00 00 01 00 00 00 0f ae f0 <48> 8b bb f8 01 00 00 48 85 ff 74 5c e8 df 40 f0 e0 48 8b 93 f8
[ 6058.869850] RIP: dvb_frontend_stop+0x30/0xd0 [dvb_core] RSP: ffffc90003077b58
[ 6058.869894] CR2: 00000000000001f8
[ 6058.875880] ---[ end trace 717eecf7193b3fc6 ]---

Signed-off-by: Matthias Schwarzott <zzam@gentoo.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/media/usb/em28xx/em28xx-dvb.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/media/usb/em28xx/em28xx-dvb.c
+++ b/drivers/media/usb/em28xx/em28xx-dvb.c
@@ -1651,6 +1651,8 @@ static int em28xx_dvb_fini(struct em28xx
prevent_sleep(&dvb->fe[1]->ops);
}

+ em28xx_unregister_dvb(dvb);
+
/* remove I2C tuner */
if (client) {
module_put(client->dev.driver->owner);
@@ -1664,7 +1666,6 @@ static int em28xx_dvb_fini(struct em28xx
i2c_unregister_device(client);
}

- em28xx_unregister_dvb(dvb);
kfree(dvb);
dev->dvb = NULL;
kref_put(&dev->ref, em28xx_free_device);
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