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

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Date:   Thu, 16 Sep 2021 17:17:27 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
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, 16 Sept 2021 at 17:08, Jason Gunthorpe <jgg@...pe.ca> wrote:
>
> 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..

Then sorry for false leads.
The second commit was from https://github.com/google/ktsan.git kcsan
branch. I am not sure if it's still present or was rebased. But either
way it's even older than the first report on upstream (we used ktsan
tree before switched to upstream).