From: Johannes Thumshirn <jthumshirn@suse.de>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Doug Gilbert <dgilbert@interlog.com>,
jejb@linux.vnet.ibm.com,
"Martin K. Petersen" <martin.petersen@oracle.com>,
linux-scsi <linux-scsi@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
axboe@kernel.dk, linux-block@vger.kernel.org,
David Rientjes <rientjes@google.com>,
syzkaller <syzkaller@googlegroups.com>,
Hannes Reinecke <hare@suse.de>
Subject: Re: scsi: use-after-free in bio_copy_from_iter
Date: Sat, 3 Dec 2016 19:19:50 +0100 [thread overview]
Message-ID: <20161203181948.GA3322@linux-x5ow.site> (raw)
In-Reply-To: <CACT4Y+bB+oxjPoC0WVCUV_Bq9ePqdV3m_V4snsfUrZ2BSWub2Q@mail.gmail.com>
On Sat, Dec 03, 2016 at 04:22:39PM +0100, Dmitry Vyukov wrote:
> On Sat, Dec 3, 2016 at 11:38 AM, Johannes Thumshirn <jthumshirn@suse.de> wrote:
> > On Fri, Dec 02, 2016 at 05:50:39PM +0100, Dmitry Vyukov wrote:
> >> On Fri, Nov 25, 2016 at 8:08 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
[...]
Hi Dmitry,
>
> Thanks for looking into this!
>
> As I noted I don't think this is use-after-free, more likely it is an
> out-of-bounds access against non-slab range.
>
> Report says that we are copying 0x1000 bytes starting at 0xffff880062c6e02a.
> The first bad address is 0xffff880062c6f000, this address was freed
> previously and that's why KASAN reports UAF.
We're copying 65499 bytes (65535 - sizeof(sg_header)) and we've got 2 order 3
page allocations to do this. It fails somewhere in there. I have seen fails at
0x2000, 0xe000 and all (0x1000 aligned) offsets inbetween.
> But this is already next page, and KASAN does not insert redzones
> around pages (only around slab allocations).
> So most likely the code should have not touch 0xffff880062c6f000 as it
> is not his memory.
> Also I noticed that the report happens after few minutes of repeatedly
> running this program, so I would expect that this is some kind of race
> -- either between kernel threads, or maybe between user space threads
> and kernel.
I somehow think it's a race as well, especially as I have to run the
reproducer in an endless loop and break out of it once I have the 1st
stacktrace in dmesg. This takes between some minutes up to one hour on my
setup.
But the race against a userspace thread... Could it be that the reproducer has
already exited it's threads while the copy_from_iter() is still running?
Normally I'd say no, as user-space shouldn't run while the kernel is doing
things in it's address space, but this is highly suspicious.
> Or maybe it's just that the next page is not always marked
> as free, so we just don't detect the bad access.
Could be, but I lack the memory management knowledge to say more than a 'could
be'.
>
> Does it all make any sense to you?
> Can you think of any additional sanity checks that will ensure that
> this code copies only memory it owns?
Given that we pass the 0xffff as dxfer_len it thinks it owns all memory, so
this is OK, kinda. All that could be would be that user-space has already
exited and thus it's memory is already freed.
Byte,
Johannes
--
Johannes Thumshirn Storage
jthumshirn@suse.de +49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)
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next prev parent reply other threads:[~2016-12-03 18:20 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-25 19:08 scsi: use-after-free in bio_copy_from_iter Dmitry Vyukov
2016-12-02 16:50 ` Dmitry Vyukov
2016-12-03 10:38 ` Johannes Thumshirn
2016-12-03 15:22 ` Dmitry Vyukov
2016-12-03 18:19 ` Johannes Thumshirn [this message]
2016-12-05 14:31 ` Dmitry Vyukov
2016-12-05 15:17 ` Johannes Thumshirn
2016-12-05 19:03 ` Al Viro
2016-12-06 9:32 ` Johannes Thumshirn
2016-12-06 9:43 ` Dmitry Vyukov
2016-12-06 15:38 ` Johannes Thumshirn
2016-12-06 15:46 ` Dmitry Vyukov
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