Return-Path: Received: from fieldses.org ([173.255.197.46]:59168 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750710AbdEIVDv (ORCPT ); Tue, 9 May 2017 17:03:51 -0400 Date: Tue, 9 May 2017 17:03:50 -0400 From: "J . Bruce Fields" To: Dan Carpenter Cc: Colin King , Ari Kauppi , Jeff Layton , linux-nfs@vger.kernel.org, kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] nfsd: avoid out of bounds read on array nfsd4_layout_ops Message-ID: <20170509210350.GD6289@fieldses.org> References: <20170509133121.26529-1-colin.king@canonical.com> <20170509140414.ycw4z6zsdevbkozm@mwanda> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20170509140414.ycw4z6zsdevbkozm@mwanda> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, May 09, 2017 at 05:04:14PM +0300, Dan Carpenter wrote: > On Tue, May 09, 2017 at 02:31:21PM +0100, Colin King wrote: > > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c > > index 1dbf62190bee..c453a1998e00 100644 > > --- a/fs/nfsd/nfs4proc.c > > +++ b/fs/nfsd/nfs4proc.c > > @@ -1259,7 +1259,8 @@ nfsd4_layout_verify(struct svc_export *exp, unsigned int layout_type) > > return NULL; > > } > > > > - if (layout_type >= 32 || !(exp->ex_layout_types & (1 << layout_type))) { > > + if (layout_type >= LAYOUT_TYPE_MAX || > > + !(exp->ex_layout_types & (1 << layout_type))) { > > The 32 is there to prevent a shift wrapping bug. The bit test prevents > a buffer overflow so this can't actually overflow. Yes, looks like a false positive for coverity. > But this change doesn't hurt and is probably cleaner. Sure. Hope it's OK if I just merge this into the previous commit: --b. commit 16b6f81d8ed9 Author: Ari Kauppi Date: Fri May 5 16:07:55 2017 -0400 nfsd: fix undefined behavior in nfsd4_layout_verify UBSAN: Undefined behaviour in fs/nfsd/nfs4proc.c:1262:34 shift exponent 128 is too large for 32-bit type 'int' Depending on compiler+architecture, this may cause the check for layout_type to succeed for overly large values (which seems to be the case with amd64). The large value will be later used in de-referencing nfsd4_layout_ops for function pointers. Reported-by: Jani Tuovila Signed-off-by: Ari Kauppi [colin.king@canonical.com: use LAYOUT_TYPE_MAX instead of 32] Reviewed-by: Dan Carpenter Signed-off-by: J. Bruce Fields diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c index d86031b6ad79..c453a1998e00 100644 --- a/fs/nfsd/nfs4proc.c +++ b/fs/nfsd/nfs4proc.c @@ -1259,7 +1259,8 @@ nfsd4_layout_verify(struct svc_export *exp, unsigned int layout_type) return NULL; } - if (!(exp->ex_layout_types & (1 << layout_type))) { + if (layout_type >= LAYOUT_TYPE_MAX || + !(exp->ex_layout_types & (1 << layout_type))) { dprintk("%s: layout type %d not supported\n", __func__, layout_type); return NULL;