linux-kernel - Re: [patch] groups: integer underflow in groups

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Date:	Mon, 23 Feb 2015 16:16:07 -0500
From:	bfields@...ldses.org (J. Bruce Fields)
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Wang YanQing <udknight@...il.com>,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [patch] groups: integer underflow in groups_alloc()

On Mon, Feb 23, 2015 at 09:03:27PM +0300, Dan Carpenter wrote:
> On Mon, Feb 23, 2015 at 11:10:02AM -0600, Eric W. Biederman wrote:
> > Dan Carpenter <dan.carpenter@...cle.com> writes:
> > 
> > > This is called from rsc_parse() with a use controlled value.  Say for
> > > example that "gidsetsize" is negative, then we could end up allocating
> > > less than sizeof(struct group_info) leading to memory corruption.
> > 
> > Right now it is the responsibility of the caller of groups_alloc to make
> > certain that gidsetsize is a valid value, and the callers of
> > groups_alloc who know what they are doing already validate this value.
> > 
> > Either the pattern of caller validates the messages needs to continue,
> > or groups_alloc needs to be changed and all of the callers need to be
> > updated.
> > 
> > Changing groups_alloc for one particular caller is just going to cause
> > maintenance problems.
> > 
> 
> This only affects NFS so let's hear from them if this limit is correct
> and decide from there.

I think that's probably the correct check, sure.

Putting it in rsc_parse sounds reasonable.

--b.
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