linux-kernel - Re: strncat() misuse (was: Re: dm_attr_{name,uuid}_show buffer overflow? (was: Re: linux-next: Tree for January 5))

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Message-ID: <20090106012759.GA3512@agk.fab.redhat.com>
Date:	Tue, 6 Jan 2009 01:27:59 +0000
From:	Alasdair G Kergon <agk@...hat.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Milan Broz <mbroz@...hat.com>,
	Jaya Kumar <jayakumar.video@...il.com>,
	Laurent Pinchart <laurent.pinchart@...net.be>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Gene Sally <Gene.Sally@...esys.com>,
	Sam Ravnborg <sam@...nborg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-next@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: strncat() misuse (was: Re: dm_attr_{name,uuid}_show buffer overflow? (was: Re: linux-next: Tree for January 5))

On Mon, Jan 05, 2009 at 11:18:38PM +0100, Geert Uytterhoeven wrote:
> On Mon, 5 Jan 2009, Geert Uytterhoeven wrote:
> > On Mon, 5 Jan 2009, Stephen Rothwell wrote:

> > |         strncat(buf, "\n", DM_NAME_LEN);
> > |         return strnlen(buf, DM_NAME_LEN);

> > Probably the intention was to limit the string in _buf_ (not the source string
> > "\n") to DM_NAME_LEN? If yes, this may cause a buffer overflow.

Both the 'n's look bogus to me as runtime checks.  But I think the code happens
to work correctly - apart from your compilation problem.

buf is always a page and both strings (name and uuid) are NULL-terminated and
the longest possible is 128 chars of uuid plus the "\n" i.e. 130 (except for a
bug I noticed on one code path which we'll fix).

Alasdair
-- 
agk@...hat.com
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