netdev - Re: [bug report] buffer overflow in isdn capi

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Date:	Tue, 01 Apr 2014 09:25:48 -0700
From:	Joe Perches <joe@...ches.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	Karsten Keil <isdn@...ux-pingi.de>, netdev@...r.kernel.org
Subject: Re: [bug report] buffer overflow in isdn capi

On Tue, 2014-04-01 at 18:48 +0300, Dan Carpenter wrote:
> The command_2_index() function is buggy and leads to a buffer overflow.
> Does anyone know how to fix this?
> 
> drivers/isdn/capi/capiutil.c
>    403  static unsigned command_2_index(unsigned c, unsigned sc)

These arguments should be u8 as well.

>    404  {
>    405          if (c & 0x80)
>    406                  c = 0x9 + (c & 0x0f);
>    407          else if (c <= 0x0f);
>    408          else if (c == 0x41)
>    409                  c = 0x9 + 0x1;
>    410          else if (c == 0xff)
>    411                  c = 0x00;
>    412          return (sc & 3) * (0x9 + 0x9) + c;
>    413  }
> 
> Imagine that we input c = 0x7f and sc = 0x3.  Then 3 * 18 + 127 = 181
> and we return 181.
> 
> The other thing that stands out to me is that the last condition
> "(c == 0xff)" is never true because then the first condition
> "(c & 0x80)" would have been true already.


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