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

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Date:   Wed, 15 Sep 2021 16:36:01 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     syzbot <syzbot+dc3dfba010d7671e05f5@...kaller.appspotmail.com>
Cc:     dledford@...hat.com, leon@...nel.org, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: use-after-free Read in addr_handler (4)

On Wed, Sep 15, 2021 at 05:41:22AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    926de8c4326c Merge tag 'acpi-5.15-rc1-3' of git://git.kern..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11fd67ed300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=37df9ef5660a8387
> dashboard link: https://syzkaller.appspot.com/bug?extid=dc3dfba010d7671e05f5
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+dc3dfba010d7671e05f5@...kaller.appspotmail.com

#syz dup: KASAN: use-after-free Write in addr_resolve (2)

Frankly, I still can't figure out how this is happening

RDMA_USER_CM_CMD_RESOLVE_IP triggers a background work and
RDMA_USER_CM_CMD_DESTROY_ID triggers destruction of the memory the
work touches.

rdma_addr_cancel() is supposed to ensure that the work isn't and won't
run.

So to hit this we have to either not call rdma_addr_cancel() when it
is need, or rdma_addr_cancel() has to be broken and continue to allow
the work.

I could find nothing along either path, though rdma_addr_cancel()
relies on some complicated properties of the workqueues I'm not
entirely positive about.

Jason