linux-kernel - Re: [syzbot] KASAN: use-after-free Read in addr

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Message-ID: <20210916150850.GN3544071@ziepe.ca>
Date:   Thu, 16 Sep 2021 12:08:50 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+dc3dfba010d7671e05f5@...kaller.appspotmail.com>,
        dledford@...hat.com, leon@...nel.org, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        Aleksandr Nogikh <nogikh@...gle.com>
Subject: Re: [syzbot] KASAN: use-after-free Read in addr_handler (4)

On Thu, Sep 16, 2021 at 04:55:16PM +0200, Dmitry Vyukov wrote:

> > I noticed we also had 2 KCSAN reports that mention rdma_resolve_addr.
> >
> > On commit 1df0d896:
> > ==================================================================
> > BUG: KCSAN: data-race in addr_handler / cma_check_port
> >
> > write to 0xffff88809fa40a1c of 4 bytes by task 21 on cpu 1:
> >  cma_comp_exch drivers/infiniband/core/cma.c:426 [inline]
> >  addr_handler+0x9f/0x2b0 drivers/infiniband/core/cma.c:3141
> >  process_one_req+0x22f/0x300 drivers/infiniband/core/addr.c:645
> >  process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
> >  worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
> >  kthread+0x20d/0x230 kernel/kthread.c:291
> >  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
> >
> > read to 0xffff88809fa40a1c of 4 bytes by task 11997 on cpu 0:
> >  cma_check_port+0xbd/0x700 drivers/infiniband/core/cma.c:3506

This has since been fixed, cma_check_port() no longer reads state

> > and on commit 5863cc79:

I can't find this commit? Current rdma_resolve_addr should not trigger
this KCSAN.

> This does not immediately explain the use-after-free for me, but these
> races suggest that everything is not protected by a single mutex and
> that there may be some surprising interleavings.
> E.g. rdma_resolve_addr checks status, and then conditionally executes
> cma_bind_addr, but the status can change concurrently.

It is true, they weren't, however I've fixed them all. These hits look
like they all from before it got fixed up..

Jason