Re: [RDMA bug] KASAN: use-after-free Read in __list_del_entry_valid (4)

[Jason Gunthorpe]

On Thu, Aug 23, 2018 at 04:39:29PM +0000, Parav Pandit wrote:
> 
> 
> > From: Jason Gunthorpe <jgg@xxxxxxxx>
> > Sent: Thursday, August 23, 2018 9:55 AM
> > To: Eric Biggers <ebiggers@xxxxxxxxxx>
> > Cc: Doug Ledford <dledford@xxxxxxxxxx>; linux-rdma@xxxxxxxxxxxxxxx;
> > dasaratharaman.chandramouli@xxxxxxxxx; Leon Romanovsky
> > <leonro@xxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; Mark Bloch
> > <markb@xxxxxxxxxxxx>; Moni Shoua <monis@xxxxxxxxxxxx>; Parav Pandit
> > <parav@xxxxxxxxxxxx>; syzkaller-bugs@xxxxxxxxxxxxxxxx; syzbot
> > <syzbot+29ee8f76017ce6cf03da@xxxxxxxxxxxxxxxxxxxxxxxxx>
> > Subject: Re: [RDMA bug] KASAN: use-after-free Read in __list_del_entry_valid
> > (4)
> > 
> > On Wed, Aug 22, 2018 at 11:16:31PM -0700, Eric Biggers wrote:
> > > Hello RDMA / InfiniBand maintainers,
> > >
> > > This is an RDMA bug and it still occurs on Linus' tree as of today
> > > (commit 815f0ddb346c1960).
> > >
> > > I've also simplified the reproducer for it; see below after the original report.
> > > Apparently it involves a race between RDMA_USER_CM_CMD_RESOLVE_IP
> > and
> > > RDMA_USER_CM_CMD_LISTEN.
> > 
> > That is an amazing reproducer!
> > 
> > I have a feeling this is the same cause as all the other syzkaller bugs in this code:
> > lack of any sane locking at all :\
> > 
> > We've talked about chucking a big lock around this whole thing, but nobody has
> > done it yet.. It isn't so simple.
> >
>
> I had some code in which reduces three locks (handler_lock,
> qp_mutex, id_lock) to single mutex to protect the cm_id and protects
> every exported symbol of rdmacm which works on cm_id.  But not ready
> enough to post it as patch yet. Lot of tests required before I get
> there and some refactor too before that.

That does sound promising..

Jason