* [PATCH] tty: Correct tty buffer flush.
@ 2012-12-03 9:54 Ilya Zykov
2013-03-04 19:19 ` Ilya Zykov
0 siblings, 1 reply; 3+ messages in thread
From: Ilya Zykov @ 2012-12-03 9:54 UTC (permalink / raw)
To: Greg Kroah-Hartman; +Cc: Alan Cox, Ben Hutchings, linux-kernel, stable
The root of problem is carelessly zeroing pointer(in function __tty_buffer_flush()),
when another thread can use it. It can be cause of "NULL pointer dereference".
Main idea of the patch, this is never release last (struct tty_buffer) in the active buffer.
Only flush data for ldisc(tty->buf.head->read = tty->buf.head->commit).
At that moment driver can collect(write) data in buffer without conflict.
It is repeat behavior of flush_to_ldisc(), only without feeding data to ldisc.
Test program and bug report you can see:
https://lkml.org/lkml/2012/11/29/368
Cc: stable@vger.kernel.org
Signed-off-by: Ilya Zykov <ilya@ilyx.ru>
---
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 6c9b7cd..4f02f9c 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -114,11 +114,14 @@ static void __tty_buffer_flush(struct tty_struct *tty)
{
struct tty_buffer *thead;
- while ((thead = tty->buf.head) != NULL) {
- tty->buf.head = thead->next;
- tty_buffer_free(tty, thead);
+ if (tty->buf.head == NULL)
+ return;
+ while ((thead = tty->buf.head->next) != NULL) {
+ tty_buffer_free(tty, tty->buf.head);
+ tty->buf.head = thead;
}
- tty->buf.tail = NULL;
+ WARN_ON(tty->buf.head != tty->buf.tail);
+ tty->buf.head->read = tty->buf.head->commit;
}
/**
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] tty: Correct tty buffer flush.
2012-12-03 9:54 [PATCH] tty: Correct tty buffer flush Ilya Zykov
@ 2013-03-04 19:19 ` Ilya Zykov
2013-03-17 4:06 ` Ben Hutchings
0 siblings, 1 reply; 3+ messages in thread
From: Ilya Zykov @ 2013-03-04 19:19 UTC (permalink / raw)
To: Ben Hutchings; +Cc: linux-kernel, stable, linux-serial
On 03.12.2012 13:54, Ilya Zykov wrote:
> The root of problem is carelessly zeroing pointer(in function __tty_buffer_flush()),
> when another thread can use it. It can be cause of "NULL pointer dereference".
> Main idea of the patch, this is never release last (struct tty_buffer) in the active buffer.
> Only flush data for ldisc(tty->buf.head->read = tty->buf.head->commit).
> At that moment driver can collect(write) data in buffer without conflict.
> It is repeat behavior of flush_to_ldisc(), only without feeding data to ldisc.
> Test program and bug report you can see:
> https://lkml.org/lkml/2012/11/29/368
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Ilya Zykov <ilya@ilyx.ru>
> ---
> diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
> index 6c9b7cd..4f02f9c 100644
> --- a/drivers/tty/tty_buffer.c
> +++ b/drivers/tty/tty_buffer.c
> @@ -114,11 +114,14 @@ static void __tty_buffer_flush(struct tty_struct *tty)
> {
> struct tty_buffer *thead;
>
> - while ((thead = tty->buf.head) != NULL) {
> - tty->buf.head = thead->next;
> - tty_buffer_free(tty, thead);
> + if (tty->buf.head == NULL)
> + return;
> + while ((thead = tty->buf.head->next) != NULL) {
> + tty_buffer_free(tty, tty->buf.head);
> + tty->buf.head = thead;
> }
> - tty->buf.tail = NULL;
> + WARN_ON(tty->buf.head != tty->buf.tail);
> + tty->buf.head->read = tty->buf.head->commit;
> }
>
> /**
>
You can include this patch, in 3.2 series , for improve stability,
it would be merged in upstream 3.9-rc1.
Thank you.
Ilya.
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/tty/tty_buffer.c?id=64325a3be08d364a62ee8f84b2cf86934bc2544a
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] tty: Correct tty buffer flush.
2013-03-04 19:19 ` Ilya Zykov
@ 2013-03-17 4:06 ` Ben Hutchings
0 siblings, 0 replies; 3+ messages in thread
From: Ben Hutchings @ 2013-03-17 4:06 UTC (permalink / raw)
To: Ilya Zykov; +Cc: linux-kernel, stable, linux-serial
[-- Attachment #1: Type: text/plain, Size: 1899 bytes --]
On Mon, 2013-03-04 at 23:19 +0400, Ilya Zykov wrote:
> On 03.12.2012 13:54, Ilya Zykov wrote:
> > The root of problem is carelessly zeroing pointer(in function __tty_buffer_flush()),
> > when another thread can use it. It can be cause of "NULL pointer dereference".
> > Main idea of the patch, this is never release last (struct tty_buffer) in the active buffer.
> > Only flush data for ldisc(tty->buf.head->read = tty->buf.head->commit).
> > At that moment driver can collect(write) data in buffer without conflict.
> > It is repeat behavior of flush_to_ldisc(), only without feeding data to ldisc.
> > Test program and bug report you can see:
> > https://lkml.org/lkml/2012/11/29/368
> >
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Ilya Zykov <ilya@ilyx.ru>
> > ---
> > diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
> > index 6c9b7cd..4f02f9c 100644
> > --- a/drivers/tty/tty_buffer.c
> > +++ b/drivers/tty/tty_buffer.c
> > @@ -114,11 +114,14 @@ static void __tty_buffer_flush(struct tty_struct *tty)
> > {
> > struct tty_buffer *thead;
> >
> > - while ((thead = tty->buf.head) != NULL) {
> > - tty->buf.head = thead->next;
> > - tty_buffer_free(tty, thead);
> > + if (tty->buf.head == NULL)
> > + return;
> > + while ((thead = tty->buf.head->next) != NULL) {
> > + tty_buffer_free(tty, tty->buf.head);
> > + tty->buf.head = thead;
> > }
> > - tty->buf.tail = NULL;
> > + WARN_ON(tty->buf.head != tty->buf.tail);
> > + tty->buf.head->read = tty->buf.head->commit;
> > }
> >
> > /**
> >
>
> You can include this patch, in 3.2 series , for improve stability,
> it would be merged in upstream 3.9-rc1.
Added to the queue, thanks.
Ben.
--
Ben Hutchings
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2012-12-03 9:54 [PATCH] tty: Correct tty buffer flush Ilya Zykov
2013-03-04 19:19 ` Ilya Zykov
2013-03-17 4:06 ` Ben Hutchings
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