On Fri, 2012-08-24 at 22:31 +0100, Sachin Prabhu wrote:
> On Fri, 2012-08-24 at 15:07 +0000, Myklebust, Trond wrote:
> > On Fri, 2012-08-24 at 15:16 +0100, Sachin Prabhu wrote:
> > > This fixes a bug introduced by commit
> > > 5a00689930ab975fdd1b37b034475017e460cf2a
> > > The patch adds an extra page to npages to hold the bitmap returned by
> > > the server.
> > >
> > > Bruce Fields pointed out that the changes introduced by the patch will
> > > cause the array npages to overflow if a buffer of size greater than or
> > > equal to XATTR_SIZE_MAX is passed to __nfs4_get_acl_uncached()
> >
> > I'd think that the right thing to do here is rather to add appropriate
> > buffer overflow checks. How about something like the following?
> >
> > 8<--------------------------------------------------------------
> > From 7c35ce220924182284aea9f8aec39b0d991600df Mon Sep 17 00:00:00 2001
> > From: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
> > Date: Fri, 24 Aug 2012 10:59:25 -0400
> > Subject: [PATCH] NFSv4: Fix range checking in __nfs4_get_acl_uncached and
> > __nfs4_proc_set_acl
> >
> > Ensure that the user supplied buffer size doesn't cause us to overflow
> > the 'pages' array.
> >
> > Also fix up some confusion between the use of PAGE_SIZE and
> > PAGE_CACHE_SIZE when calculating buffer sizes. We're not using
> > the page cache for anything here.
> >
> > Signed-off-by: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
>
> This patch is susceptible to the problem described in commit
> 5a00689930ab975fdd1b37b034475017e460cf2a
>
> This can be demonstrated by the following patch to pynfs which pads the
> bitmap with 1000 extra elements.
>
> To reproduce, on the server
> cd newpynfs/nfs4.0/
> ./setup.py build_ext --inplace
> ./nfs4server.py
>
> on the client,
> mount -o vers=4 SERVER:/ /mnt
> touch /mnt/a
> nfs4_getfacl /mnt/a
>
> With this new patch, you will get a general protection fault in
> _copy_from_pages().
Is this on a kernel with commit 519d3959e30a98f8e135e7a16647c10af5ad63d5
(NFSv4: Fix pointer arithmetic in decode_getacl) applied?
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
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