Re: [PATCH] Avoid array overflow in __nfs4_get_acl_uncached

[Sachin Prabhu <sprabhu@redhat.com>]

On Fri, 2012-08-24 at 21:38 +0000, Myklebust, Trond wrote:
> 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@netapp.com>
> > > 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@netapp.com>
> > 
> > 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?
> 

Yes.

Sachin Prabhu