[PATCH] [media] dvbdev: add a mutex protecting the "mdev" pointer
From: Max Kellermann
Date: Thu May 03 2018 - 14:21:23 EST
During destruction, a race condition in
dvb_media_controller_disable_source() can cause a kernel crash,
because the "mdev" pointer has been read successfully while another
task executes dvb_usb_media_device_unregister(), which destroys the
object. Example for such a crash:
general protection fault: 0000 [#1] SMP
CPU: 1 PID: 301 Comm: vdr Not tainted 4.8.1-nuc+ #102
[142B blob data]
task: ffff8802301f2040 task.stack: ffff880233728000
RIP: 0010:[<ffffffff816c296b>] [<ffffffff816c296b>] dvb_frontend_release+0xcb/0x120
RSP: 0018:ffff88023372bdd8 EFLAGS: 00010202
RAX: 001fd55c000000da RBX: ffff880236bad810 RCX: 0000000000000000
RDX: ffff880235bd81f0 RSI: 0000000000000246 RDI: ffff880235bd81e8
RBP: ffff88023372be00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: ffff88022f009910 R12: 0000000000000000
R13: ffff880235a21a80 R14: ffff880235bd8000 R15: ffff880235bb8a78
FS: 0000000000000000(0000) GS:ffff88023fd00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f96edd69818 CR3: 0000000002406000 CR4: 00000000001006e0
Stack:
ffff88022f009900 0000000000000008 ffff880235bb8a78 ffff8802344fbb20
ffff880236437b40 ffff88023372be48 ffffffff8117a81e ffff880235bb8a78
ffff88022f009910 ffff8802335a7400 ffff8802301f2040 ffff88022f009900
Call Trace:
[<ffffffff8117a81e>] __fput+0xde/0x1d0
[<ffffffff8117a949>] ____fput+0x9/0x10
[<ffffffff810a9fce>] task_work_run+0x7e/0xa0
[<ffffffff81094bab>] do_exit+0x27b/0xa50
[<ffffffff810407e3>] ? __do_page_fault+0x1c3/0x430
[<ffffffff81095402>] do_group_exit+0x42/0xb0
[<ffffffff8109547f>] SyS_exit_group+0xf/0x10
[<ffffffff8108bedb>] entry_SYSCALL_64_fastpath+0x13/0x8f
Code: 31 c9 49 8d be e8 01 00 00 ba 01 00 00 00 be 03 00 00 00 e8 68 2d a0 ff 48 8b 83 10 03 00 00 48 8b 80 88 00 00 00 48 85 c0 74 12 <48> 8b 80 88 02 00 00 48 85 c0 74 06 49 8b 7d
RIP [<ffffffff816c296b>] dvb_frontend_release+0xcb/0x120
Signed-off-by: Max Kellermann <max.kellermann@xxxxxxxxx>
---
drivers/media/dvb-core/dvb_frontend.c | 7 +++++++
drivers/media/dvb-core/dvbdev.c | 4 ++++
drivers/media/usb/dvb-usb/dvb-usb-dvb.c | 4 ++++
include/media/dvbdev.h | 2 ++
4 files changed, 17 insertions(+)
diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c
index a4ada1ccf0df..bba3dbb9154e 100644
--- a/drivers/media/dvb-core/dvb_frontend.c
+++ b/drivers/media/dvb-core/dvb_frontend.c
@@ -2732,6 +2732,7 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
fepriv->voltage = -1;
#ifdef CONFIG_MEDIA_CONTROLLER_DVB
+ mutex_lock(&fe->dvb->mdev_lock);
if (fe->dvb->mdev) {
mutex_lock(&fe->dvb->mdev->graph_mutex);
if (fe->dvb->mdev->enable_source)
@@ -2740,11 +2741,13 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
&fepriv->pipe);
mutex_unlock(&fe->dvb->mdev->graph_mutex);
if (ret) {
+ mutex_unlock(&fe->dvb->mdev_lock);
dev_err(fe->dvb->device,
"Tuner is busy. Error %d\n", ret);
goto err2;
}
}
+ mutex_unlock(&fe->dvb->mdev_lock);
#endif
ret = dvb_frontend_start (fe);
if (ret)
@@ -2762,12 +2765,14 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
err3:
#ifdef CONFIG_MEDIA_CONTROLLER_DVB
+ mutex_lock(&fe->dvb->mdev_lock);
if (fe->dvb->mdev) {
mutex_lock(&fe->dvb->mdev->graph_mutex);
if (fe->dvb->mdev->disable_source)
fe->dvb->mdev->disable_source(dvbdev->entity);
mutex_unlock(&fe->dvb->mdev->graph_mutex);
}
+ mutex_unlock(&fe->dvb->mdev_lock);
err2:
#endif
dvb_generic_release(inode, file);
@@ -2799,12 +2804,14 @@ static int dvb_frontend_release(struct inode *inode, struct file *file)
if (dvbdev->users == -1) {
wake_up(&fepriv->wait_queue);
#ifdef CONFIG_MEDIA_CONTROLLER_DVB
+ mutex_lock(&fe->dvb->mdev_lock);
if (fe->dvb->mdev) {
mutex_lock(&fe->dvb->mdev->graph_mutex);
if (fe->dvb->mdev->disable_source)
fe->dvb->mdev->disable_source(dvbdev->entity);
mutex_unlock(&fe->dvb->mdev->graph_mutex);
}
+ mutex_unlock(&fe->dvb->mdev_lock);
#endif
if (fe->exit != DVB_FE_NO_EXIT)
wake_up(&dvbdev->wait_queue);
diff --git a/drivers/media/dvb-core/dvbdev.c b/drivers/media/dvb-core/dvbdev.c
index 787fe06df217..b44232f03c42 100644
--- a/drivers/media/dvb-core/dvbdev.c
+++ b/drivers/media/dvb-core/dvbdev.c
@@ -859,6 +859,10 @@ int dvb_register_adapter(struct dvb_adapter *adap, const char *name,
adap->mfe_dvbdev = NULL;
mutex_init (&adap->mfe_lock);
+#ifdef CONFIG_MEDIA_CONTROLLER_DVB
+ mutex_init (&adap->mdev_lock);
+#endif
+
list_add_tail (&adap->list_head, &dvb_adapter_list);
mutex_unlock(&dvbdev_register_lock);
diff --git a/drivers/media/usb/dvb-usb/dvb-usb-dvb.c b/drivers/media/usb/dvb-usb/dvb-usb-dvb.c
index 3a66e732e0d8..8056053c9ab0 100644
--- a/drivers/media/usb/dvb-usb/dvb-usb-dvb.c
+++ b/drivers/media/usb/dvb-usb/dvb-usb-dvb.c
@@ -132,10 +132,14 @@ static void dvb_usb_media_device_unregister(struct dvb_usb_adapter *adap)
if (!adap->dvb_adap.mdev)
return;
+ mutex_lock(&adap->dvb_adap.mdev_lock);
+
media_device_unregister(adap->dvb_adap.mdev);
media_device_cleanup(adap->dvb_adap.mdev);
kfree(adap->dvb_adap.mdev);
adap->dvb_adap.mdev = NULL;
+
+ mutex_unlock(&adap->dvb_adap.mdev_lock);
#endif
}
diff --git a/include/media/dvbdev.h b/include/media/dvbdev.h
index ee91516ad074..881ca461b7bb 100644
--- a/include/media/dvbdev.h
+++ b/include/media/dvbdev.h
@@ -91,6 +91,7 @@ struct dvb_frontend;
* @mfe_dvbdev: Frontend device in use, in the case of MFE
* @mfe_lock: Lock to prevent using the other frontends when MFE is
* used.
+ * @mdev_lock: Protect access to the mdev pointer.
* @mdev: pointer to struct media_device, used when the media
* controller is used.
* @conn: RF connector. Used only if the device has no separate
@@ -114,6 +115,7 @@ struct dvb_adapter {
struct mutex mfe_lock; /* access lock for thread creation */
#if defined(CONFIG_MEDIA_CONTROLLER_DVB)
+ struct mutex mdev_lock;
struct media_device *mdev;
struct media_entity *conn;
struct media_pad *conn_pads;
--
2.17.0