From: Dmitry Vyukov <dvyukov@google.com>
To: Johannes Thumshirn <jthumshirn@suse.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
syzkaller <syzkaller@googlegroups.com>,
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>,
Hannes Reinecke <hare@suse.de>, Michal Hocko <mhocko@suse.cz>
Subject: Re: scsi: use-after-free in bio_copy_from_iter
Date: Tue, 6 Dec 2016 10:43:57 +0100 [thread overview]
Message-ID: <CACT4Y+abaYf-o_i-jyGsZiG2RH7eTHtZNYcmao_uZaH-F+T+YQ@mail.gmail.com> (raw)
In-Reply-To: <20161206093257.GC4818@linux-x5ow.site>
On Tue, Dec 6, 2016 at 10:32 AM, Johannes Thumshirn <jthumshirn@suse.de> wrote:
> On Mon, Dec 05, 2016 at 07:03:39PM +0000, Al Viro wrote:
>> On Mon, Dec 05, 2016 at 04:17:53PM +0100, Johannes Thumshirn wrote:
>> > 633 hp = &srp->header;
>> > [...]
>> > 646 hp->dxferp = (char __user *)buf + cmd_size;
>>
>> > So the memory for hp->dxferp comes from:
>> > 633 hp = &srp->header;
>>
>> ????
>>
>> > >From my debug instrumentation I see that the dxferp ends up in the
>> > iovec_iter's kvec->iov_base and the faulting address is always dxferp + n *
>> > 4k with n in [1, 16] (and we're copying 16 4k pages from the iovec into the
>> > bio).
>>
>> _Address_ of hp->dxferp comes from that assignment; the value is 'buf'
>> argument of sg_write() + small offset. In this case, it should point
>> inside a pipe buffer, which is, indeed, at a kernel address. Who'd
>> allocated srp is irrelevant.
>
> Yes I realized that as well when I had enough distance between me and the
> code...
>
>>
>> And if you end up dereferencing more than one page worth there, you do have
>> a problem - pipe buffers are not going to be that large. Could you slap
>> WARN_ON((size_t)input_size > count);
>> right after the calculation of input_size in sg_write() and see if it triggers
>> on your reproducer?
>
> I did and it didn't trigger. What triggers is (as expected) a
> WARN_ON((size_t)mxsize > count);
> We have count at 80 and mxsize (which ends in hp->dxfer_len) at 65499. But the
> 65499 bytes are the len of the data we're suppost to be copying in via the
> iov. I'm still rather confused what's happening here, sorry.
I think the critical piece here is some kind of race or timing
condition. Note that the test program executes all of
memfd_create/write/open/sendfile twice. Second time the calls race
with each other, but they also can race with the first execution of
the calls.
next prev parent reply other threads:[~2016-12-06 9:44 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
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 [this message]
2016-12-06 15:38 ` Johannes Thumshirn
2016-12-06 15:46 ` Dmitry Vyukov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CACT4Y+abaYf-o_i-jyGsZiG2RH7eTHtZNYcmao_uZaH-F+T+YQ@mail.gmail.com \
--to=dvyukov@google.com \
--cc=axboe@kernel.dk \
--cc=dgilbert@interlog.com \
--cc=hare@suse.de \
--cc=jejb@linux.vnet.ibm.com \
--cc=jthumshirn@suse.de \
--cc=linux-block@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-scsi@vger.kernel.org \
--cc=martin.petersen@oracle.com \
--cc=mhocko@suse.cz \
--cc=rientjes@google.com \
--cc=syzkaller@googlegroups.com \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).