Re: [PATCH] NFSv4: Fix a NULL pointer dereference in pnfs_mark_matching_lsegs_return()

[Trond Myklebust <trondmy@hammerspace.com>]

On Wed, 2021-05-19 at 12:06 -0400, schumaker.anna@gmail.com wrote:
> From: Anna Schumaker <Anna.Schumaker@Netapp.com>
> 
> Commit de144ff4234f changes _pnfs_return_layout() to call
> pnfs_mark_matching_lsegs_return() passing NULL as the struct
> pnfs_layout_range argument. Unfortunately,
> pnfs_mark_matching_lsegs_return() doesn't check if we have a value
> here
> before dereferencing it, causing an oops.
> 
> I'm able to hit this crash consistently when running connectathon
> basic
> tests on NFS v4.1/v4.2 against Ontap.
> 
> Fixes: de144ff4234f ("NFSv4: Don't discard segments marked for return
> in _pnfs_return_layout()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
> ---
>  fs/nfs/pnfs.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
> index 03e0b34c4a64..6d720afb7b70 100644
> --- a/fs/nfs/pnfs.c
> +++ b/fs/nfs/pnfs.c
> @@ -2484,12 +2484,12 @@ pnfs_mark_matching_lsegs_return(struct
> pnfs_layout_hdr *lo,
>                         set_bit(NFS_LSEG_LAYOUTRETURN, &lseg-
> >pls_flags);
>                 }
>  
> -       if (remaining) {
> +       if (remaining && return_range) {
>                 pnfs_set_plh_return_info(lo, return_range->iomode,
> seq);
>                 return -EBUSY;
>         }
>  
> -       if (!list_empty(&lo->plh_return_segs)) {
> +       if (return_range && !list_empty(&lo->plh_return_segs)) {
>                 pnfs_set_plh_return_info(lo, return_range->iomode,
> seq);
>                 return 0;

This patch would mean we fail to mark the layout for return in
situations where we clearly should be doing so. The lack of a
return_range doesn't indicate that we don't want to return any layouts,
but rather that we want to return all layouts.

I suggest rather changing the caller, _pnfs_return_layout() to move
that declaration of 'struct pnfs_layout_range range' out of the if
statement so that it can be passed as an argument instead of NULL.

>         }

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com