Re: Sometimes DVB broken with commit 6769a0b7ee0c3b
From: Mauro Carvalho Chehab
Date: Wed Jun 14 2023 - 18:20:35 EST
Em Mon, 12 Jun 2023 17:10:06 +0200
"Linux regression tracking (Thorsten Leemhuis)" <regressions@xxxxxxxxxxxxx> escreveu:
> On 05.06.23 20:00, Mauro Carvalho Chehab wrote:
> > Em Mon, 5 Jun 2023 12:44:43 +0200
> > Thorsten Leemhuis <regressions@xxxxxxxxxxxxx> escreveu:
> >> On 05.06.23 12:37, Mauro Carvalho Chehab wrote:
> >>> Em Mon, 5 Jun 2023 11:38:49 +0200
> >>> "Linux regression tracking (Thorsten Leemhuis)" <regressions@xxxxxxxxxxxxx> escreveu:
> >>>>
> >>>> On 30.05.23 13:12, Thomas Voegtle wrote:
> >>>>>
> >>>>> I have the problem that sometimes my DVB card does not initialize
> >>>>> properly booting Linux 6.4-rc4.
> >>>>> This is not always, maybe in 3 out of 4 attempts.
> >>>>> When this happens somehow you don't see anything special in dmesg, but
> >>>>> the card just doesn't work.
> >>>>>
> >>>>> Reverting this helps:
> >>>>> commit 6769a0b7ee0c3b31e1b22c3fadff2bfb642de23f
> >>>>[...]
> >>>> Mauro: I wonder if this is something you or someone else has to look
> >>>> into, as Hyunwoo Kim posted a few times per months to Linux lists, but
> >>>> according to a quick search on lore hasn't posted anything since ~two
> >>>> months now. :-/
> >>>
> >>> Yeah, I was slow applying this one, as I was afraid of it to cause
> >>> troubles. The DVB frontend state machine is complex, and uses a
> >>> semaphore to update its state. There was some past attempts of
> >>> addressing some lifetime issues there that we ended needing to revert
> >>> or not being applied, as the fix caused more harm than good.
> >>> [...]
> >>
> >> Thx for the update. That's unfortunate, but how it is sometimes. Which
> >> leads to a follow-up question: is reverting the culprit temporarily an
> >> option? Or did those old use-after-free problems became known to be a
> >> problem we can't live with anymore for another few months?
> >
> > Reverting the patch seems to be the way to proceed. Then, work on another
> > way to address UAF.
> >
> > I'm not aware of dvb users complaining about troubles due to UAF, although
> > it seems that there's now a CVE for it. So, maybe someone complained against
> > a distro Kernel, which caused the CVE to be opened.
> >
> > So, while it is nice to have the lifetime issues fixed, last time I checked,
> > the USB dvb-usb/dvb-usb-v2 have some logic that usually prevents it to cause
> > real issues during device removal, and unbinding DVB PCIe devices is
> > something that users don't do in practice.
>
> Thx for the explanation and handling this. I noticed you posted a
> revert, but it misses a fixes tag for the reverted commit and a Link: or
> Closes: tag to the report.
I added a Fixed and a link (see patch enclosed).
If everything merges fine on linux-next, I should be sending a PR
upstream likely tomorrow.
Regards,
Mauro
[PATCH] Revert "media: dvb-core: Fix use-after-free on race condition at dvb_frontend"
As reported by Thomas Voegtle <tv@xxxxxxxx>, 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@xxxxxxxx/
Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c
index bc6950a5740f..9293b058ab99 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 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
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 367d5381217b..e7c44870f20d 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;
};
/**