Revert "media: dvb-core: Fix use-after-free on race condition at dvb_frontend"

As reported by Thomas Voegtle <tv@lio96.de>, sometimes a DVB card does
not initialize properly booting Linux 6.4-rc4. This is not always, maybe
in 3 out of 4 attempts.

After double-checking, the root cause seems to be related to the
UAF fix, which is causing a race issue:

[   26.332149] tda10071 7-0005: found a 'NXP TDA10071' in cold state, will try to load a firmware
[   26.340779] tda10071 7-0005: downloading firmware from file 'dvb-fe-tda10071.fw'
[  989.277402] INFO: task vdr:743 blocked for more than 491 seconds.
[  989.283504]       Not tainted 6.4.0-rc5-i5 #249
[  989.288036] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  989.295860] task:vdr             state:D stack:0     pid:743   ppid:711    flags:0x00004002
[  989.295865] Call Trace:
[  989.295867]  <TASK>
[  989.295869]  __schedule+0x2ea/0x12d0
[  989.295877]  ? asm_sysvec_apic_timer_interrupt+0x16/0x20
[  989.295881]  schedule+0x57/0xc0
[  989.295884]  schedule_preempt_disabled+0xc/0x20
[  989.295887]  __mutex_lock.isra.16+0x237/0x480
[  989.295891]  ? dvb_get_property.isra.10+0x1bc/0xa50
[  989.295898]  ? dvb_frontend_stop+0x36/0x180
[  989.338777]  dvb_frontend_stop+0x36/0x180
[  989.338781]  dvb_frontend_open+0x2f1/0x470
[  989.338784]  dvb_device_open+0x81/0xf0
[  989.338804]  ? exact_lock+0x20/0x20
[  989.338808]  chrdev_open+0x7f/0x1c0
[  989.338811]  ? generic_permission+0x1a2/0x230
[  989.338813]  ? link_path_walk.part.63+0x340/0x380
[  989.338815]  ? exact_lock+0x20/0x20
[  989.338817]  do_dentry_open+0x18e/0x450
[  989.374030]  path_openat+0xca5/0xe00
[  989.374031]  ? terminate_walk+0xec/0x100
[  989.374034]  ? path_lookupat+0x93/0x140
[  989.374036]  do_filp_open+0xc0/0x140
[  989.374038]  ? __call_rcu_common.constprop.91+0x92/0x240
[  989.374041]  ? __check_object_size+0x147/0x260
[  989.374043]  ? __check_object_size+0x147/0x260
[  989.374045]  ? alloc_fd+0xbb/0x180
[  989.374048]  ? do_sys_openat2+0x243/0x310
[  989.374050]  do_sys_openat2+0x243/0x310
[  989.374052]  do_sys_open+0x52/0x80
[  989.374055]  do_syscall_64+0x5b/0x80
[  989.421335]  ? __task_pid_nr_ns+0x92/0xa0
[  989.421337]  ? syscall_exit_to_user_mode+0x20/0x40
[  989.421339]  ? do_syscall_64+0x67/0x80
[  989.421341]  ? syscall_exit_to_user_mode+0x20/0x40
[  989.421343]  ? do_syscall_64+0x67/0x80
[  989.421345]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
[  989.421348] RIP: 0033:0x7fe895d067e3
[  989.421349] RSP: 002b:00007fff933c2ba0 EFLAGS: 00000293 ORIG_RAX: 0000000000000101
[  989.421351] RAX: ffffffffffffffda RBX: 00007fff933c2c10 RCX: 00007fe895d067e3
[  989.421352] RDX: 0000000000000802 RSI: 00005594acdce160 RDI: 00000000ffffff9c
[  989.421353] RBP: 0000000000000802 R08: 0000000000000000 R09: 0000000000000000
[  989.421353] R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000001
[  989.421354] R13: 00007fff933c2ca0 R14: 00000000ffffffff R15: 00007fff933c2c90
[  989.421355]  </TASK>

This reverts commit 6769a0b7ee0c3b31e1b22c3fadff2bfb642de23f.

Fixes: 6769a0b7ee0c ("media: dvb-core: Fix use-after-free on race condition at dvb_frontend")
Link: https://lore.kernel.org/all/da5382ad-09d6-20ac-0d53-611594b30861@lio96.de/
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

2 files changed, 10 insertions, 49 deletions

diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c
index bc6950a5740f6a..9293b058ab9974 100644
--- a/drivers/media/dvb-core/dvb_frontend.c
+++ b/drivers/media/dvb-core/dvb_frontend.c
@@ -817,26 +817,15 @@ static void dvb_frontend_stop(struct dvb_frontend *fe)
 
 	dev_dbg(fe->dvb->device, "%s:\n", __func__);
 
-	mutex_lock(&fe->remove_mutex);
-
 	if (fe->exit != DVB_FE_DEVICE_REMOVED)
 		fe->exit = DVB_FE_NORMAL_EXIT;
 	mb();
 
-	if (!fepriv->thread) {
-		mutex_unlock(&fe->remove_mutex);
+	if (!fepriv->thread)
 		return;
-	}
 
 	kthread_stop(fepriv->thread);
 
-	mutex_unlock(&fe->remove_mutex);
-
-	if (fepriv->dvbdev->users < -1) {
-		wait_event(fepriv->dvbdev->wait_queue,
-			   fepriv->dvbdev->users == -1);
-	}
-
 	sema_init(&fepriv->sem, 1);
 	fepriv->state = FESTATE_IDLE;
 
@@ -2780,13 +2769,9 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
 	struct dvb_adapter *adapter = fe->dvb;
 	int ret;
 
-	mutex_lock(&fe->remove_mutex);
-
 	dev_dbg(fe->dvb->device, "%s:\n", __func__);
-	if (fe->exit == DVB_FE_DEVICE_REMOVED) {
-		ret = -ENODEV;
-		goto err_remove_mutex;
-	}
+	if (fe->exit == DVB_FE_DEVICE_REMOVED)
+		return -ENODEV;
 
 	if (adapter->mfe_shared == 2) {
 		mutex_lock(&adapter->mfe_lock);
@@ -2794,8 +2779,7 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
 			if (adapter->mfe_dvbdev &&
 			    !adapter->mfe_dvbdev->writers) {
 				mutex_unlock(&adapter->mfe_lock);
-				ret = -EBUSY;
-				goto err_remove_mutex;
+				return -EBUSY;
 			}
 			adapter->mfe_dvbdev = dvbdev;
 		}
@@ -2818,10 +2802,8 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
 			while (mferetry-- && (mfedev->users != -1 ||
 					      mfepriv->thread)) {
 				if (msleep_interruptible(500)) {
-					if (signal_pending(current)) {
-						ret = -EINTR;
-						goto err_remove_mutex;
-					}
+					if (signal_pending(current))
+						return -EINTR;
 				}
 			}
 
@@ -2833,8 +2815,7 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
 				if (mfedev->users != -1 ||
 				    mfepriv->thread) {
 					mutex_unlock(&adapter->mfe_lock);
-					ret = -EBUSY;
-					goto err_remove_mutex;
+					return -EBUSY;
 				}
 				adapter->mfe_dvbdev = dvbdev;
 			}
@@ -2893,8 +2874,6 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
 
 	if (adapter->mfe_shared)
 		mutex_unlock(&adapter->mfe_lock);
-
-	mutex_unlock(&fe->remove_mutex);
 	return ret;
 
 err3:
@@ -2916,9 +2895,6 @@ err1:
 err0:
 	if (adapter->mfe_shared)
 		mutex_unlock(&adapter->mfe_lock);
-
-err_remove_mutex:
-	mutex_unlock(&fe->remove_mutex);
 	return ret;
 }
 
@@ -2929,8 +2905,6 @@ static int dvb_frontend_release(struct inode *inode, struct file *file)
 	struct dvb_frontend_private *fepriv = fe->frontend_priv;
 	int ret;
 
-	mutex_lock(&fe->remove_mutex);
-
 	dev_dbg(fe->dvb->device, "%s:\n", __func__);
 
 	if ((file->f_flags & O_ACCMODE) != O_RDONLY) {
@@ -2952,18 +2926,10 @@ static int dvb_frontend_release(struct inode *inode, struct file *file)
 		}
 		mutex_unlock(&fe->dvb->mdev_lock);
 #endif
+		if (fe->exit != DVB_FE_NO_EXIT)
+			wake_up(&dvbdev->wait_queue);
 		if (fe->ops.ts_bus_ctrl)
 			fe->ops.ts_bus_ctrl(fe, 0);
-
-		if (fe->exit != DVB_FE_NO_EXIT) {
-			mutex_unlock(&fe->remove_mutex);
-			wake_up(&dvbdev->wait_queue);
-		} else {
-			mutex_unlock(&fe->remove_mutex);
-		}
-
-	} else {
-		mutex_unlock(&fe->remove_mutex);
 	}
 
 	dvb_frontend_put(fe);
@@ -3064,7 +3030,6 @@ int dvb_register_frontend(struct dvb_adapter *dvb,
 	fepriv = fe->frontend_priv;
 
 	kref_init(&fe->refcount);
-	mutex_init(&fe->remove_mutex);
 
 	/*
 	 * After initialization, there need to be two references: one
diff --git a/include/media/dvb_frontend.h b/include/media/dvb_frontend.h
index 367d5381217b58..e7c44870f20de4 100644
--- a/include/media/dvb_frontend.h
+++ b/include/media/dvb_frontend.h
@@ -686,10 +686,7 @@ struct dtv_frontend_properties {
  * @id:			Frontend ID
  * @exit:		Used to inform the DVB core that the frontend
  *			thread should exit (usually, means that the hardware
- *			got disconnected).
- * @remove_mutex:	mutex that avoids a race condition between a callback
- *			called when the hardware is disconnected and the
- *			file_operations of dvb_frontend.
+ *			got disconnected.
  */
 
 struct dvb_frontend {
@@ -707,7 +704,6 @@ struct dvb_frontend {
 	int (*callback)(void *adapter_priv, int component, int cmd, int arg);
 	int id;
 	unsigned int exit;
-	struct mutex remove_mutex;
 };
 
 /**