Re: [PATCH] NFS: fs_context: validate UDP retrans to prevent shift out-of-bounds

[Trond Myklebust]

Hi Randy,

On Tue, 2021-03-16 at 15:35 -0700, Randy Dunlap wrote:
> ping?
> 

I can take this patch for the next merge window.

> On 3/1/21 4:19 PM, Randy Dunlap wrote:
> > Fix shift out-of-bounds in xprt_calc_majortimeo(). This is caused
> > by a garbage timeout (retrans) mount option being passed to nfs
> > mount,
> > in this case from syzkaller.
> > 
> > If the protocol is XPRT_TRANSPORT_UDP, then 'retrans' is a shift
> > value for a 64-bit long integer, so 'retrans' cannot be >= 64.
> > If it is >= 64, fail the mount and return an error.
> > 
> > Fixes: 9954bf92c0cd ("NFS: Move mount parameterisation bits into
> > their own file")
> > Reported-by: syzbot+ba2e91df8f74809417fa@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Reported-by: syzbot+f3a0fa110fd630ab56c8@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> > Cc: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> > Cc: Anna Schumaker <anna.schumaker@xxxxxxxxxx>
> > Cc: linux-nfs@xxxxxxxxxxxxxxx
> > Cc: David Howells <dhowells@xxxxxxxxxx>
> > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > ---
> >  fs/nfs/fs_context.c |   12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> > 
> > --- lnx-512-rc1.orig/fs/nfs/fs_context.c
> > +++ lnx-512-rc1/fs/nfs/fs_context.c
> > @@ -974,6 +974,15 @@ static int nfs23_parse_monolithic(struct
> >                                sizeof(mntfh->data) - mntfh->size);
> >  
> >                 /*
> > +                * for proto == XPRT_TRANSPORT_UDP, which is what
> > uses
> > +                * to_exponential, implying shift: limit the shift
> > value
> > +                * to BITS_PER_LONG (majortimeo is unsigned long)
> > +                */
> > +               if (!(data->flags & NFS_MOUNT_TCP)) /* this will be
> > UDP */
> > +                       if (data->retrans >= 64) /* shift value is
> > too large */
> > +                               goto out_invalid_data;
> > +
> > +               /*
> >                  * Translate to nfs_fs_context, which
> > nfs_fill_super
> >                  * can deal with.
> >                  */
> > @@ -1073,6 +1082,9 @@ out_no_address:
> >  
> >  out_invalid_fh:
> >         return nfs_invalf(fc, "NFS: invalid root filehandle");
> > +
> > +out_invalid_data:
> > +       return nfs_invalf(fc, "NFS: invalid binary mount data");
> >  }
> >  
> >  #if IS_ENABLED(CONFIG_NFS_V4)
> > 
> 
> 

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