RE: [PATCH 12/32] Blackfin arch: Fix bug using usb keyboard crashes kernel

RE: [PATCH 12/32] Blackfin arch: Fix bug using usb keyboard crashes kernel

[Hennerich, Michael]

I'm also not an expert...
  
But without conswitchp preset (potential fix):

During initcalls: con_init is called, and returns because of
!display_desc.

static int __init con_init(void)
{
	const char *display_desc = NULL;
	struct vc_data *vc;
	unsigned int currcons = 0, i;

	acquire_console_sem();

	if (conswitchp)
		display_desc = conswitchp->con_startup();
	if (!display_desc) {
		fg_console = 0;
		release_console_sem();
		return 0; // RETURNS HERE
	}

--snip--

}

At this point there is no memory allocated for vc_cons[].d
A bit later vty_init calls kbd_init.

int __init vty_init(void)
{

--snip--
	kbd_init();
--snip--

}

>From now on events are passed to kbd_event which will then call
kbd_keycode.
I don't see where vc_cons[].d in between there is initialized.
 

>-----Original Message-----
>From: penberg@gmail.com [mailto:penberg@gmail.com] On Behalf Of Pekka
>Enberg
>Sent: Montag, 21. Mai 2007 14:51
>To: Hennerich, Michael
>Cc: Bryan Wu; torvalds@linux-foundation.org; akpm@linux-foundation.org;
>linux-kernel@vger.kernel.org
>Subject: Re: [PATCH 12/32] Blackfin arch: Fix bug using usb keyboard
>crashes kernel
>
>On 5/21/07, Hennerich, Michael <Michael.Hennerich@analog.com> wrote:
>> With CONFIG_VT (drivers/char/vt.c) enabled and a USB HID keyboard
>connected,
>> we were seeing bad pointer dereferences in drivers/char/keyboard.c
>>
>> In function kbd_keycode vc_cons[fg_console].d was un-initialized.
>
>On 5/21/07, Pekka Enberg <penberg@cs.helsinki.fi> wrote:
>> Makes sense. Please consider adding this to the changelog. Thanks.
>
>I am not an expert on this, but I don't see how vc_cons[fg_console].d
>would be uninitialized. It is always set in
>drivers/char/vt.c:con_init() and drivers/char/vt.c:vc_allocate(). The
>conswitchp change affects vc->vc_sw but I don't see that being used in
>drivers/char/keyboard.c:kbd_keycode() except indirectly via
>set_console et al.
>
>Perhaps I am missing something here?

Re: [PATCH 12/32] Blackfin arch: Fix bug using usb keyboard crashes kernel

[Pekka Enberg]

Hi Michael,

On 5/21/07, Hennerich, Michael <Michael.Hennerich@analog.com> wrote:
> During initcalls: con_init is called, and returns because of
> !display_desc.

[snip]

Aah, I missed that bit.

On 5/21/07, Hennerich, Michael <Michael.Hennerich@analog.com> wrote:
> I don't see where vc_cons[].d in between there is initialized.

Indeed. Your fix looks good. Thanks again for the explanation.

Re: [PATCH 12/32] Blackfin arch: Fix bug using usb keyboard crashes kernel

[Pekka Enberg]

On 5/21/07, Hennerich, Michael <Michael.Hennerich@analog.com> wrote:
> With CONFIG_VT (drivers/char/vt.c) enabled and a USB HID keyboard connected,
> we were seeing bad pointer dereferences in drivers/char/keyboard.c
>
> In function kbd_keycode vc_cons[fg_console].d was un-initialized.

On 5/21/07, Pekka Enberg <penberg@cs.helsinki.fi> wrote:
> Makes sense. Please consider adding this to the changelog. Thanks.

I am not an expert on this, but I don't see how vc_cons[fg_console].d
would be uninitialized. It is always set in
drivers/char/vt.c:con_init() and drivers/char/vt.c:vc_allocate(). The
conswitchp change affects vc->vc_sw but I don't see that being used in
drivers/char/keyboard.c:kbd_keycode() except indirectly via
set_console et al.

Perhaps I am missing something here?

Re: [PATCH 12/32] Blackfin arch: Fix bug using usb keyboard crashes kernel

[Pekka Enberg]

On 5/21/07, Hennerich, Michael <Michael.Hennerich@analog.com> wrote:
> I was fixing this issue some time ago.

[snip]

Makes sense. Please consider adding this to the changelog. Thanks.

                        Pekka

RE: [PATCH 12/32] Blackfin arch: Fix bug using usb keyboard crashes kernel

[Hennerich, Michael]

I was fixing this issue some time ago.

With CONFIG_VT (drivers/char/vt.c) enabled and a USB HID keyboard connected, we were seeing bad pointer dereferences in drivers/char/keyboard.c

In function kbd_keycode vc_cons[fg_console].d was un-initialized .

static void kbd_keycode(unsigned int keycode, int down, int hw_raw)
{
--snip--
	struct vc_data *vc = vc_cons[fg_console].d;

--snip--
	tty = vc->vc_tty;
--snip--
}	

The workaround, almost any arch does is to initialize conswitchp with the dummy console.

conswitchp = &dummy_con;	

The dummy console gets automatically selected if there is no other suitable console (VGA).
The bit we were missing is simply this fix.

Best regards,
Michael


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>-----Original Message-----
>From: penberg@gmail.com [mailto:penberg@gmail.com] On Behalf Of Pekka
>Enberg
>Sent: Montag, 21. Mai 2007 13:40
>To: Bryan Wu
>Cc: torvalds@linux-foundation.org; akpm@linux-foundation.org; linux-
>kernel@vger.kernel.org; Michael Hennerich
>Subject: Re: [PATCH 12/32] Blackfin arch: Fix bug using usb keyboard
>crashes kernel
>
>Hi Bryan,
>
>On 5/21/07, Bryan Wu <bryan.wu@analog.com> wrote:
>> +#ifdef CONFIG_DUMMY_CONSOLE
>> +       conswitchp = &dummy_con;
>> +#endif
>>         cclk = get_cclk();
>>         sclk = get_sclk();
>
>This patch has no changelog. While it is probably apparent to you why
>this fixes a crash when using an USB keyboard, it would be nice for
>the rest of us to know which crash it fixes and why.

Re: [PATCH 12/32] Blackfin arch: Fix bug using usb keyboard crashes kernel

[Pekka Enberg]

Hi Bryan,

On 5/21/07, Bryan Wu <bryan.wu@analog.com> wrote:
> +#ifdef CONFIG_DUMMY_CONSOLE
> +       conswitchp = &dummy_con;
> +#endif
>         cclk = get_cclk();
>         sclk = get_sclk();

This patch has no changelog. While it is probably apparent to you why
this fixes a crash when using an USB keyboard, it would be nice for
the rest of us to know which crash it fixes and why.

[PATCH 12/32] Blackfin arch: Fix bug using usb keyboard crashes kernel

[Bryan Wu]

From: Michael Hennerich <michael.hennerich@analog.com>

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>
---
 arch/blackfin/kernel/setup.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/arch/blackfin/kernel/setup.c b/arch/blackfin/kernel/setup.c
index 342bb8d..c456ee5 100644
--- a/arch/blackfin/kernel/setup.c
+++ b/arch/blackfin/kernel/setup.c
@@ -33,7 +33,6 @@
 #include <linux/seq_file.h>
 #include <linux/cpu.h>
 #include <linux/module.h>
-#include <linux/console.h>
 #include <linux/tty.h>
 
 #include <linux/ext2_fs.h>
@@ -175,6 +174,9 @@ void __init setup_arch(char **cmdline_p)
 	unsigned long mtd_phys = 0;
 #endif
 
+#ifdef CONFIG_DUMMY_CONSOLE
+	conswitchp = &dummy_con;
+#endif
 	cclk = get_cclk();
 	sclk = get_sclk();
 
-- 
1.5.1.2