Re: [PATCH] sunrpc: Avoid a KASAN slab-out-of-bounds bug in xdr_set_page_base()

["J. Bruce Fields" <bfields@fieldses.org>]

On Thu, Aug 26, 2021 at 04:42:21PM -0400, J. Bruce Fields wrote:
> On Thu, Aug 26, 2021 at 03:44:32PM -0400, Anna Schumaker wrote:
> > On Thu, Aug 12, 2021 at 4:32 PM J. Bruce Fields <bfields@fieldses.org> wrote:
> > >
> > > On Mon, Jun 14, 2021 at 07:14:40PM -0400, bfields wrote:
> > > > On Wed, Jun 09, 2021 at 05:07:29PM -0400, schumaker.anna@gmail.com wrote:
> > > > > From: Anna Schumaker <Anna.Schumaker@Netapp.com>
> > > > >
> > > > > This seems to happen fairly easily during READ_PLUS testing on NFS v4.2.
> > > >
> > > > Yep, I hit a KASAN warning here every time, and this fixes it,
> > > > thanks.--b.
> > >
> > > By the way, config NFS_V4_2_READ_PLUS still says:
> > >
> > >         This is intended for developers only. The READ_PLUS operation
> > >         has been shown to have issues under specific conditions and
> > >         should not be used in production.
> > >
> > > But this warning was the only thing I was seeing.  Is there another
> > > known issue remaining?
> > 
> > I think it was an issue around using lseek to generate the reply. The
> > file contents could change between each call, leading to inconsistent
> > results (and a new failing xfstest that previously passed)
> 
> OK, thanks, I see now that you mentioned in 21e31401fc45 "NFS: Disable
> READ_PLUS by default" that there were generic/091 and generic/263
> failures.
> 
> Looks like they're both testing concurrent direct and buffered IO.  I
> don't know what we try to guarantee in that case.

But I'd assumed generic/263 just wasn't supported on nfs anyway.--b.

generic/263 81s ... [failed, exit status 1]- output mismatch (see /root/xfstests-dev/results//generic/263.out.bad)
    --- tests/generic/263.out	2019-12-20 17:34:10.493343575 -0500
    +++ /root/xfstests-dev/results//generic/263.out.bad	2021-08-26 16:43:40.751891500 -0400
    @@ -1,3 +1,262 @@
     QA output created by 263
     fsx -N 10000 -o 8192 -l 500000 -r PSIZE -t BSIZE -w BSIZE -Z
     fsx -N 10000 -o 128000 -l 500000 -r PSIZE -t BSIZE -w BSIZE -Z
    +Seed set to 1
    +main: filesystem does not support fallocate mode FALLOC_FL_KEEP_SIZE, disabling!
    +main: filesystem does not support fallocate mode FALLOC_FL_ZERO_RANGE, disabling!
    +main: filesystem does not support fallocate mode FALLOC_FL_COLLAPSE_RANGE, disabling!
    ...
    (Run 'diff -u /root/xfstests-dev/tests/generic/263.out /root/xfstests-dev/results//generic/263.out.bad'  to see the entire diff)
Ran: generic/263
Failures: generic/263
Failed 1 of 1 tests