linux-kernel - Re: [PATCH 1/1] USB: serial/usb_wwan, fix tty NULL dereference

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Date:	Tue, 15 Feb 2011 20:14:50 +0300
From:	Sergei Shtylyov <sshtylyov@...sta.com>
To:	Jiri Slaby <jslaby@...e.cz>
CC:	gregkh@...e.de, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, jirislaby@...il.com,
	Amit Shah <amitshah@....net>, baoyb <baoyb@...t.org.cn>
Subject: Re: [PATCH 1/1] USB: serial/usb_wwan, fix tty NULL dereference

Hello.

Jiri Slaby wrote:

> tty_port_tty_get may return without any problems NULL. Handle this
> case and do not oops in usb_wwan_indat_callback by dereferencing it.

> The oops:
> Unable to handle kernel paging request for data at address 0x000000d8
> Faulting instruction address: 0xc0175b3c
> Oops: Kernel access of bad area, sig: 11 [#1]
> PowerPC 40x Platform
> last sysfs file:
> /sys/devices/pci0000:00/0000:00:00.0/0000:01:00.0/0000:02:09.2/usb1/idVendor
> Modules linked in:
> NIP: c0175b3c LR: c0175e7c CTR: c0215c90
> REGS: c77f7d50 TRAP: 0300   Not tainted  (2.6.37-rc5)
> MSR: 00021030 <ME,CE,IR,DR>  CR: 88482028  XER: 2000005f
> DEAR: 000000d8, ESR: 00000000
> TASK = c7141b90[1149] 'wvdial' THREAD: c2750000
> GPR00: 00021030 c77f7e00 c7141b90 00000000 0000000e 00000000 0000000e c0410680
> GPR08: c683db00 00000000 00000001 c03c81f8 88482028 10073ef4 ffffffb9 ffffff94
> GPR16: 00000000 fde036c0 00200200 00100100 00000001 ffffff8d c34fabcc 00000000
> GPR24: c71120d4 00000000 00000000 0000000e 00021030 00000000 00000000 0000000e
> NIP [c0175b3c] tty_buffer_request_room+0x2c/0x194
> LR [c0175e7c] tty_insert_flip_string_fixed_flag+0x3c/0xb0
> Call Trace:
> [c77f7e00] [00000003] 0x3 (unreliable)
> [c77f7e30] [c0175e7c] tty_insert_flip_string_fixed_flag+0x3c/0xb0
> [c77f7e60] [c0215df4] usb_wwan_indat_callback+0x164/0x170
> ...

> References: https://bugzilla.kernel.org/show_bug.cgi?id=24582
> Cc: Amit Shah <amitshah@....net>
> Cc: baoyb <baoyb@...t.org.cn>
> Cc: Greg Kroah-Hartman <gregkh@...e.de>
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
> ---
>  drivers/usb/serial/usb_wwan.c |   15 +++++++++------
>  1 files changed, 9 insertions(+), 6 deletions(-)

> diff --git a/drivers/usb/serial/usb_wwan.c b/drivers/usb/serial/usb_wwan.c
> index b004b2a..9c014e2 100644
> --- a/drivers/usb/serial/usb_wwan.c
> +++ b/drivers/usb/serial/usb_wwan.c
> @@ -295,12 +295,15 @@ static void usb_wwan_indat_callback(struct urb *urb)
>  		    __func__, status, endpoint);
>  	} else {
>  		tty = tty_port_tty_get(&port->port);
> -		if (urb->actual_length) {
> -			tty_insert_flip_string(tty, data, urb->actual_length);
> -			tty_flip_buffer_push(tty);
> -		} else
> -			dbg("%s: empty read urb received", __func__);
> -		tty_kref_put(tty);
> +		if (tty) {
> +			if (urb->actual_length) {
> +				tty_insert_flip_string(tty, data,
> +						urb->actual_length);
> +				tty_flip_buffer_push(tty);
> +			} else
> +				dbg("%s: empty read urb received", __func__);

    Should be {} on the *else* branch too, according to Documentation/CodingStyle...

WBR, Sergei
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