linux-kernel - Re: [syzbot] [iommu?] KASAN: slab-use-after-free Read in iommufd_ioas_iova

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Message-ID: <20231025183220.GQ691768@ziepe.ca>
Date:   Wed, 25 Oct 2023 15:32:20 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     syzbot <syzbot+45f6cae2ca8c1f71e529@...kaller.appspotmail.com>
Cc:     iommu@...ts.linux.dev, joro@...tes.org, kevin.tian@...el.com,
        linux-kernel@...r.kernel.org, robin.murphy@....com,
        syzkaller-bugs@...glegroups.com, will@...nel.org
Subject: Re: [syzbot] [iommu?] KASAN: slab-use-after-free Read in
 iommufd_ioas_iova_ranges

On Wed, Oct 25, 2023 at 06:11:01AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    c3200081020d Merge tag 'block-6.6-2023-10-20' of git://git..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15013471680000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=849fe52ba7c6d78a
> dashboard link: https://syzkaller.appspot.com/bug?extid=45f6cae2ca8c1f71e529
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/caa5c1eed3ec/disk-c3200081.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/7990a3a9f71e/vmlinux-c3200081.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/015551ac9acc/bzImage-c3200081.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+45f6cae2ca8c1f71e529@...kaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: slab-use-after-free in __up_read+0xb3/0x690 kernel/locking/rwsem.c:1342
> Read of size 8 at addr ffff8880283c9068 by task syz-executor.2/30372

Oh *ugh* I knew about this limitation once and forgot about it
apparently.

  CPU 0         CPU1
 down_read()
 up_read()
                down_write()
                up_write()
		kfree()
 [..]
  tail portion of up_read()

I suppose the rwsem should be turned into a refcount and completion

Jason