linux-kernel - Re: [PATCH] dvb: fix potential format string leak

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Message-ID: <CAOcJUbxhwQQJudR1sz5rcEQb6V+AdcB0HUBAdsHZWoSZ2CBXmw@mail.gmail.com>
Date:	Mon, 30 Sep 2013 12:20:48 -0400
From:	Michael Krufky <mkrufky@...uxtv.org>
To:	Joe Perches <joe@...ches.com>
Cc:	Kees Cook <keescook@...omium.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	linux-media <linux-media@...r.kernel.org>
Subject: Re: [PATCH] dvb: fix potential format string leak

On Mon, Sep 16, 2013 at 7:48 PM, Joe Perches <joe@...ches.com> wrote:
> On Mon, 2013-09-16 at 16:37 -0700, Kees Cook wrote:
>> Make sure that a format string cannot accidentally leak into the printk
>> buffer.
> []
>> diff --git a/drivers/media/dvb-frontends/dib9000.c b/drivers/media/dvb-frontends/dib9000.c
> []
>> @@ -649,7 +649,7 @@ static int dib9000_risc_debug_buf(struct dib9000_state *state, u16 * data, u8 si
>>       b[2 * (size - 2) - 1] = '\0';   /* Bullet proof the buffer */
>>       if (*b == '~') {
>>               b++;
>> -             dprintk(b);
>> +             dprintk("%s", b);
>>       } else
>>               dprintk("RISC%d: %d.%04d %s", state->fe_id, ts / 10000, ts % 10000, *b ? b : "<emtpy>");
>>       return 1;
>
> This looks odd.
>
> Perhaps this should be:
>
>         if (*b == '~')
>                 b++;
>         dprintk("etc...);
>
> It'd be nice to fix the <empty> typo too.

This *does* look odd, I agree.  Meanwhile, I do believe this patch
leaves things better than before.  I'm going to merge Kees' patch for
now, but it would be nice to see a better cleanup for that code block.

-Mike Krufky
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