* [PATCH] n_gsm: Add Mutex to avoid race when net destroy
@ 2013-02-28 5:31 channing
2013-02-28 9:53 ` Jiri Slaby
0 siblings, 1 reply; 6+ messages in thread
From: channing @ 2013-02-28 5:31 UTC (permalink / raw)
To: Greg Kroah-Hartman, Jiri Slaby; +Cc: linux-kernel
when gsm Net is enabled, data on dlci is transferrd by
gsm_mux_net_start_xmit(), while userspace may trigger
ioctrl to call gsm_destroy_network() during data was
transferring, because there is no mutex protection between
the two functions, following scenario may happen:
1) gsm_mux_net_start_xmit() calls muxnet_get(mux_net);
2) gsm_destroy_network() is called from ioctrl, and it
will not call net_free() to release net device because
net device is still referred in step 1)
3) continue execute step 1), gsm_mux_net_start_xmit()
calls muxnet_put(mux_net), and then calls net_free() to
release net device.
4) if userspace triggers gsm_create_network() at same time
with net_free() in step 3). it will hit race on dlci->net.
This patch is to add a mutex in tx function to avoid race
between it and destroy function.
Signed-off-by: Chao Bi <chao.bi@intel.com>
Signed-off-by: Pillet Vincent <vincentx.pillet@intel.com>
---
drivers/tty/n_gsm.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 4a43ef5..0ca810a 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2660,6 +2660,7 @@ static int gsm_mux_net_start_xmit(struct sk_buff *skb,
{
struct gsm_mux_net *mux_net = (struct gsm_mux_net *)netdev_priv(net);
struct gsm_dlci *dlci = mux_net->dlci;
+ mutex_lock(&dlci->mutex);
muxnet_get(mux_net);
skb_queue_head(&dlci->skb_list, skb);
@@ -2669,6 +2670,7 @@ static int gsm_mux_net_start_xmit(struct sk_buff *skb,
/* And tell the kernel when the last transmit started. */
net->trans_start = jiffies;
muxnet_put(mux_net);
+ mutex_unlock(&dlci->mutex);
return NETDEV_TX_OK;
}
--
1.7.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] n_gsm: Add Mutex to avoid race when net destroy
2013-02-28 5:31 [PATCH] n_gsm: Add Mutex to avoid race when net destroy channing
@ 2013-02-28 9:53 ` Jiri Slaby
2013-03-01 8:51 ` channing
0 siblings, 1 reply; 6+ messages in thread
From: Jiri Slaby @ 2013-02-28 9:53 UTC (permalink / raw)
To: channing, Greg Kroah-Hartman; +Cc: linux-kernel, ML netdev
On 02/28/2013 06:31 AM, channing wrote:
>
> when gsm Net is enabled, data on dlci is transferrd by
> gsm_mux_net_start_xmit(), while userspace may trigger
> ioctrl to call gsm_destroy_network() during data was
> transferring, because there is no mutex protection between
> the two functions, following scenario may happen:
>
> 1) gsm_mux_net_start_xmit() calls muxnet_get(mux_net);
> 2) gsm_destroy_network() is called from ioctrl, and it
> will not call net_free() to release net device because
> net device is still referred in step 1)
> 3) continue execute step 1), gsm_mux_net_start_xmit()
> calls muxnet_put(mux_net), and then calls net_free() to
> release net device.
> 4) if userspace triggers gsm_create_network() at same time
> with net_free() in step 3). it will hit race on dlci->net.
>
> This patch is to add a mutex in tx function to avoid race
> between it and destroy function.
>
> Signed-off-by: Chao Bi <chao.bi@intel.com>
> Signed-off-by: Pillet Vincent <vincentx.pillet@intel.com>
> ---
> drivers/tty/n_gsm.c | 2 ++
> 1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
> index 4a43ef5..0ca810a 100644
> --- a/drivers/tty/n_gsm.c
> +++ b/drivers/tty/n_gsm.c
> @@ -2660,6 +2660,7 @@ static int gsm_mux_net_start_xmit(struct sk_buff *skb,
> {
> struct gsm_mux_net *mux_net = (struct gsm_mux_net *)netdev_priv(net);
> struct gsm_dlci *dlci = mux_net->dlci;
> + mutex_lock(&dlci->mutex);
Nack, start_xmit may be called in an atomic context -- you cannot call
mutex.
> muxnet_get(mux_net);
>
> skb_queue_head(&dlci->skb_list, skb);
> @@ -2669,6 +2670,7 @@ static int gsm_mux_net_start_xmit(struct sk_buff *skb,
> /* And tell the kernel when the last transmit started. */
> net->trans_start = jiffies;
> muxnet_put(mux_net);
Instead the concept is broken. If this was the last reference (as
described in your steps above), it would blow up for the same reason I
refer to above, i.e. net_free here would call unregister_netdev which is
not atomic. Plus it will definitely deadlock because unregister_netdev
waits for start_xmit to finish.
It should stop the queue and schedule a workqueue to lock the mutex,
unregister the hetdev and reset dlci->net. (Or maybe just call
muxnet_put with the lock held.)
That will fix 4), but there is still a bug: what protects
gsm_create_network to be called twice or more in a sequence thus
re-setting dlci->net to a new and new pointer?
> + mutex_unlock(&dlci->mutex);
> return NETDEV_TX_OK;
> }
thanks,
--
js
suse labs
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] n_gsm: Add Mutex to avoid race when net destroy
2013-02-28 9:53 ` Jiri Slaby
@ 2013-03-01 8:51 ` channing
2013-03-01 9:10 ` Jiri Slaby
0 siblings, 1 reply; 6+ messages in thread
From: channing @ 2013-03-01 8:51 UTC (permalink / raw)
To: Jiri Slaby; +Cc: Greg Kroah-Hartman, linux-kernel, ML netdev, vincentx.pillet
On Thu, 2013-02-28 at 10:53 +0100, Jiri Slaby wrote:
> On 02/28/2013 06:31 AM, channing wrote:
> >
> > when gsm Net is enabled, data on dlci is transferrd by
> > gsm_mux_net_start_xmit(), while userspace may trigger
> > ioctrl to call gsm_destroy_network() during data was
> > transferring, because there is no mutex protection between
> > the two functions, following scenario may happen:
> >
> > 1) gsm_mux_net_start_xmit() calls muxnet_get(mux_net);
> > 2) gsm_destroy_network() is called from ioctrl, and it
> > will not call net_free() to release net device because
> > net device is still referred in step 1)
> > 3) continue execute step 1), gsm_mux_net_start_xmit()
> > calls muxnet_put(mux_net), and then calls net_free() to
> > release net device.
> > 4) if userspace triggers gsm_create_network() at same time
> > with net_free() in step 3). it will hit race on dlci->net.
> >
> > This patch is to add a mutex in tx function to avoid race
> > between it and destroy function.
> >
> > Signed-off-by: Chao Bi <chao.bi@intel.com>
> > Signed-off-by: Pillet Vincent <vincentx.pillet@intel.com>
> > ---
> > drivers/tty/n_gsm.c | 2 ++
> > 1 files changed, 2 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
> > index 4a43ef5..0ca810a 100644
> > --- a/drivers/tty/n_gsm.c
> > +++ b/drivers/tty/n_gsm.c
> > @@ -2660,6 +2660,7 @@ static int gsm_mux_net_start_xmit(struct sk_buff *skb,
> > {
> > struct gsm_mux_net *mux_net = (struct gsm_mux_net *)netdev_priv(net);
> > struct gsm_dlci *dlci = mux_net->dlci;
> > + mutex_lock(&dlci->mutex);
>
> Nack, start_xmit may be called in an atomic context -- you cannot call
> mutex.
>
> > muxnet_get(mux_net);
> >
> > skb_queue_head(&dlci->skb_list, skb);
> > @@ -2669,6 +2670,7 @@ static int gsm_mux_net_start_xmit(struct sk_buff *skb,
> > /* And tell the kernel when the last transmit started. */
> > net->trans_start = jiffies;
> > muxnet_put(mux_net);
>
> Instead the concept is broken. If this was the last reference (as
> described in your steps above), it would blow up for the same reason I
> refer to above, i.e. net_free here would call unregister_netdev which is
> not atomic. Plus it will definitely deadlock because unregister_netdev
> waits for start_xmit to finish.
>
> It should stop the queue and schedule a workqueue to lock the mutex,
> unregister the hetdev and reset dlci->net. (Or maybe just call
> muxnet_put with the lock held.)
Thanks, Jiri, you're right, I didn't notice that in validation because
DEBUG_ATOMIC_SLEEP is not enabled in my platform :( Now I'm trying to
work out the workqueue solution, when it finished I'll re-submit for
review. What do you mean by "call muxnet_put with lock held"? do you
mean to use spin lock instead of mutex?
>
> That will fix 4), but there is still a bug: what protects
> gsm_create_network to be called twice or more in a sequence thus
> re-setting dlci->net to a new and new pointer?
Yes, that's a problem, Vincent has already noticed that and has a check
in gsmtty_ioctl to avoid call net creation multi time, I thought it
might be patch for other issue so didn't put them together.
>
> > + mutex_unlock(&dlci->mutex);
> > return NETDEV_TX_OK;
> > }
>
> thanks,
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] n_gsm: Add Mutex to avoid race when net destroy
2013-03-01 8:51 ` channing
@ 2013-03-01 9:10 ` Jiri Slaby
2013-03-01 11:04 ` Bi, Chao
0 siblings, 1 reply; 6+ messages in thread
From: Jiri Slaby @ 2013-03-01 9:10 UTC (permalink / raw)
To: channing; +Cc: Greg Kroah-Hartman, linux-kernel, ML netdev, vincentx.pillet
On 03/01/2013 09:51 AM, channing wrote:
>> It should stop the queue and schedule a workqueue to lock the mutex,
>> unregister the hetdev and reset dlci->net. (Or maybe just call
>> muxnet_put with the lock held.)
>
> Thanks, Jiri, you're right, I didn't notice that in validation because
> DEBUG_ATOMIC_SLEEP is not enabled in my platform :( Now I'm trying to
> work out the workqueue solution, when it finished I'll re-submit for
> review. What do you mean by "call muxnet_put with lock held"? do you
> mean to use spin lock instead of mutex?
No, I mean, in the newly added scheduled work, to lock the mutex and
simply call muxnet_put. That should fix it, right?
--
js
suse labs
^ permalink raw reply [flat|nested] 6+ messages in thread
* RE: [PATCH] n_gsm: Add Mutex to avoid race when net destroy
2013-03-01 9:10 ` Jiri Slaby
@ 2013-03-01 11:04 ` Bi, Chao
0 siblings, 0 replies; 6+ messages in thread
From: Bi, Chao @ 2013-03-01 11:04 UTC (permalink / raw)
To: Jiri Slaby; +Cc: Greg Kroah-Hartman, linux-kernel, ML netdev, Pillet, VincentX
[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="utf-8", Size: 1513 bytes --]
-----Original Message-----
From: Jiri Slaby [mailto:jirislaby@gmail.com] On Behalf Of Jiri Slaby
Sent: Friday, March 01, 2013 5:10 PM
To: Bi, Chao
Cc: Greg Kroah-Hartman; linux-kernel@vger.kernel.org; ML netdev; Pillet, VincentX
Subject: Re: [PATCH] n_gsm: Add Mutex to avoid race when net destroy
On 03/01/2013 09:51 AM, channing wrote:
>> It should stop the queue and schedule a workqueue to lock the mutex,
>> unregister the hetdev and reset dlci->net. (Or maybe just call
>> muxnet_put with the lock held.)
>
> Thanks, Jiri, you're right, I didn't notice that in validation because
> DEBUG_ATOMIC_SLEEP is not enabled in my platform :( Now I'm trying to
> work out the workqueue solution, when it finished I'll re-submit for
> review. What do you mean by "call muxnet_put with lock held"? do you
> mean to use spin lock instead of mutex?
No, I mean, in the newly added scheduled work, to lock the mutex and simply call muxnet_put. That should fix it, right?
[chao] Yes, that's to only move muxnet_put to scheduled work with mutex protected, and the rest of gsm_mux_net_start_xmit()
Is kept unchanged, and they are not in mutex lock. It could avoid race of net_free().
I'm not sure if it's safe enough, I mean if dlci->net is released before STATS(net) in gsm_mux_net_start_xmit(), will STATS(net) access unreliable data?
--
js
suse labs
ÿôèº{.nÇ+·®+%Ëÿ±éݶ\x17¥wÿº{.nÇ+·¥{±þG«éÿ{ayº\x1dÊÚë,j\a¢f£¢·hïêÿêçz_è®\x03(éÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?¨èÚ&£ø§~á¶iOæ¬z·vØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?I¥
^ permalink raw reply [flat|nested] 6+ messages in thread
* RE: [PATCH] n_gsm: Add Mutex to avoid race when net destroy
@ 2013-03-01 11:04 ` Bi, Chao
0 siblings, 0 replies; 6+ messages in thread
From: Bi, Chao @ 2013-03-01 11:04 UTC (permalink / raw)
To: Jiri Slaby; +Cc: Greg Kroah-Hartman, linux-kernel, ML netdev, Pillet, VincentX
-----Original Message-----
From: Jiri Slaby [mailto:jirislaby@gmail.com] On Behalf Of Jiri Slaby
Sent: Friday, March 01, 2013 5:10 PM
To: Bi, Chao
Cc: Greg Kroah-Hartman; linux-kernel@vger.kernel.org; ML netdev; Pillet, VincentX
Subject: Re: [PATCH] n_gsm: Add Mutex to avoid race when net destroy
On 03/01/2013 09:51 AM, channing wrote:
>> It should stop the queue and schedule a workqueue to lock the mutex,
>> unregister the hetdev and reset dlci->net. (Or maybe just call
>> muxnet_put with the lock held.)
>
> Thanks, Jiri, you're right, I didn't notice that in validation because
> DEBUG_ATOMIC_SLEEP is not enabled in my platform :( Now I'm trying to
> work out the workqueue solution, when it finished I'll re-submit for
> review. What do you mean by "call muxnet_put with lock held"? do you
> mean to use spin lock instead of mutex?
No, I mean, in the newly added scheduled work, to lock the mutex and simply call muxnet_put. That should fix it, right?
[chao] Yes, that's to only move muxnet_put to scheduled work with mutex protected, and the rest of gsm_mux_net_start_xmit()
Is kept unchanged, and they are not in mutex lock. It could avoid race of net_free().
I'm not sure if it's safe enough, I mean if dlci->net is released before STATS(net) in gsm_mux_net_start_xmit(), will STATS(net) access unreliable data?
--
js
suse labs
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2013-03-01 11:04 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2013-02-28 5:31 [PATCH] n_gsm: Add Mutex to avoid race when net destroy channing
2013-02-28 9:53 ` Jiri Slaby
2013-03-01 8:51 ` channing
2013-03-01 9:10 ` Jiri Slaby
2013-03-01 11:04 ` Bi, Chao
2013-03-01 11:04 ` Bi, Chao
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.