linux-kernel - Re: [14/17] nfsd: wrong index used in inner loop

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Date:	Thu, 17 Mar 2011 19:00:12 -0400
From:	"J. Bruce Fields" <bfields@...hat.com>
To:	Tim Gardner <tim.gardner@...onical.com>
Cc:	Greg KH <gregkh@...e.de>, alan@...rguk.ukuu.org.uk,
	Roel Kluin <roel.kluin@...il.com>,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org
Subject: Re: [14/17] nfsd: wrong index used in inner loop

On Fri, Mar 11, 2011 at 10:21:58PM +0000, Tim Gardner wrote:
> On 03/11/2011 08:40 PM, Greg KH wrote:
> >2.6.32-longterm review patch.  If anyone has any objections, please let us know.
> >
> >------------------
> >
> >From: roel<roel.kluin@...il.com>
> >
> >commit 3ec07aa9522e3d5e9d5ede7bef946756e623a0a0 upstream.
> >
> >Index i was already used in the outer loop
> >
> >Signed-off-by: Roel Kluin<roel.kluin@...il.com>
> >Signed-off-by: J. Bruce Fields<bfields@...hat.com>
> >Signed-off-by: Greg Kroah-Hartman<gregkh@...e.de>
> >
> >---
> >  fs/nfsd/nfs4xdr.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> >--- a/fs/nfsd/nfs4xdr.c
> >+++ b/fs/nfsd/nfs4xdr.c
> >@@ -1114,7 +1114,7 @@ nfsd4_decode_create_session(struct nfsd4
> >
> >  	u32 dummy;
> >  	char *machine_name;
> >-	int i;
> >+	int i, j;
> >  	int nr_secflavs;
> >
> >  	READ_BUF(16);
> >@@ -1187,7 +1187,7 @@ nfsd4_decode_create_session(struct nfsd4
> >  			READ_BUF(4);
> >  			READ32(dummy);
> >  			READ_BUF(dummy * 4);
> >-			for (i = 0; i<  dummy; ++i)
> >+			for (j = 0; j<  dummy; ++j)
> >  				READ32(dummy);
> >  			break;
> >  		case RPC_AUTH_GSS:
> >
> >
> >--
> 
> I agree that fixing the index in this loop is a good thing, but its
> caused me to look at the result:
> 
> for (j = 0; j<  dummy; ++j)
> 	READ32(dummy);
> 
> It seems to me that this loop might never terminate if the original
> buffer is maliciously constructed, e.g., 0, 1, 2, 3, ... Is the data
> in this buffer really that well vetted?

Agreed, the code's still clearly bogus.  In fact, we can just delete
that loop entirely; I have a patch queued up to send to Linus soon.

(But go ahead and apply this anyway, and then you'll get the followup
patch when it lands.)

--b.
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