linux-kernel - Re: [PATCH 1/1] staging/speakup/kobjects.c: Code improvement.

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Date:	Wed, 11 Sep 2013 02:12:29 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Chris Brannon <chris@...-brannons.com>
Cc:	Raphael S Carvalho <raphael.scarv@...il.com>,
	devel@...verdev.osuosl.org, Kirk Reiser <kirk@...sers.ca>,
	speakup@...ille.uwo.ca,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org,
	Samuel Thibault <samuel.thibault@...-lyon.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH 1/1] staging/speakup/kobjects.c: Code improvement.

Good eye for spotting the memory corruption bug!

This is a bug fix, so the fix should go in a separate patch and not
merged with a code cleanup patch.  Ordinary users can trigger this so
it's a security bug and separating it out is extra important.

The checking in spk_set_num_var() is not sufficient as well.  If we use
E_INC then we can hit an integer overflow bug:

drivers/staging/speakup/varhandlers.c
   198                  if (how == E_SET)
   199                          val = input;
   200                  else
   201                          val = var_data->u.n.value;
   202                  if (how == E_INC)
   203                          val += input;

"input" comes from the user.  This addition can overflow so that input
is a very high number and now "val" is a low enough number.

   204                  else if (how == E_DEC)
   205                          val -= input;
   206                  if (val < var_data->u.n.low || val > var_data->u.n.high)
   207                          return -ERANGE;

"val" is valid, but "input" is not valid.  We use "input" in the caller
function as the index to an array.

   208          }

I guess that's simple enough to fix but why is the caller using "input"
instead of "val"?

regards,
dan carpenter

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