linux-kernel - Re: scsi: sg: assorted memory corruptions

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Date:   Thu, 1 Feb 2018 01:03:40 -0500
From:   Douglas Gilbert <dgilbert@...erlog.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Bart Van Assche <Bart.VanAssche@....com>,
        "jejb@...ux.vnet.ibm.com" <jejb@...ux.vnet.ibm.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "ben.hutchings@...ethink.co.uk" <ben.hutchings@...ethink.co.uk>,
        "syzkaller@...glegroups.com" <syzkaller@...glegroups.com>
Subject: Re: scsi: sg: assorted memory corruptions

On 2018-01-30 07:22 AM, Dmitry Vyukov wrote:
> Uh, I've answered this a week ago, but did not notice that Doug
> dropped everybody from CC. Reporting to all.
> 
> On Mon, Jan 22, 2018 at 8:16 PM, Douglas Gilbert <dgilbert@...erlog.com> wrote:
>> On 2018-01-22 02:06 PM, Dmitry Vyukov wrote:
>>>
>>> On Mon, Jan 22, 2018 at 7:57 PM, Douglas Gilbert <dgilbert@...erlog.com>
>> Please show me the output of 'lsscsi -g' on your test machine.
>> /dev/sg0 is often associated with /dev/sda which is often a SATA
>> SSD (or a virtualized one) that holds the root file system.
>> With the sg pass-through driver it is relatively easy to write
>> random (user provided data) over the root file system which will
>> almost certainly "root" the system.
> 
> 
> This is pretty standard qemu vm started with:
> 
> qemu-system-x86_64 -hda wheezy.img -net user,host=10.0.2.10 -net nic
> -nographic -kernel arch/x86/boot/bzImage -append "console=ttyS0
> root=/dev/sda earlyprintk=serial " -m 2G -smp 4
> 
> # lsscsi -g
> [0:0:0:0]    disk    ATA      QEMU HARDDISK    0     /dev/sda   /dev/sg0

With lk 4.15.0-rc9 I can run your test program (with some additions, see
attachment) for 30 minutes against a scsi_debug simulated disk. You can
easily replicate this test just run 'modprobe scsi_debug' and a third
line should appear in your lsscsi output. The new device will most likely
be /dev/sg2 .

With lk 4.15.0 (release) running against a SAS SSD (SEAGATE ST200FM0073),
the test has  been running 20 minutes and counting without problems. That
is using a LSI HBA with the mpt3sas driver.

> [1:0:0:0]    cd/dvd  QEMU     QEMU DVD-ROM     2.0.  /dev/sr0   /dev/sg1
> 
> # readlink /sys/class/scsi_generic/sg0
> ../../devices/pci0000:00/0000:00:01.1/ata1/host0/target0:0:0/0:0:0:0/scsi_generic/sg0
> 
> # cat /sys/class/scsi_generic/sg0/device/vendor
> ATA

^^^^^
That subsystem is the culprit IMO, most likely libata.

Until you can show this test failing on something other than an
ATA disk, then I will treat this issue as closed.

Doug Gilbert


>>>> Perhaps it misbehaves when it
>>>> gets a SCSI command in the T10 range (i.e. not vendor specific) with
>>>> a 9 byte cdb length. As far as I'm aware T10 (and the Ansi committee
>>>> before it) have never defined a cdb with an odd length.
>>>>
>>>> For those that are not aware, the sg driver is a relatively thin
>>>> shim over the block layer, the SCSI mid-level, and a low-level
>>>> driver which may have another kernel driver stack underneath it
>>>> (e.g. UAS (USB attached SCSI)). The previous report from syzkaller
>>>> on the sg driver ("scsi: memory leak in sg_start_req") has resulted
>>>> in one accepted patch on the block layer with probably more to
>>>> come in the same area.
>>>>
>>>> Testing the patch Dmitry gave (with some added error checks which
>>>> reported no problems) with the scsi_debug driver supplying /dev/sg0
>>>> I have not seen any problems running that test program. Again
>>>> there might be a very slow memory leak, but if there is I don't
>>>> believe it is in the sg driver.
>>>
>>>
>>> Did you run it in a loop? First runs pass just fine for me too.
>>
>>
>> Is thirty minutes long enough ??
> 
> 
> Yes, it certainly should be enough. Here is what I see:
> 
> 
> # while ./a.out; do echo RUN; done
> RUN
> RUN
> RUN
> RUN
> RUN
> RUN
> RUN
> [  371.977266] ==================================================================
> [  371.980158] BUG: KASAN: double-free or invalid-free in
> __put_task_struct+0x1e7/0x5c0
> ....
> 
> 
> Here is full execution trace of the write call if that will be of any help:
> https://gist.githubusercontent.com/dvyukov/14ae64c3e753dedf9ab2608676ecf0b9/raw/9803d52bb1e317a9228e362236d042aaf0fa9d69/gistfile1.txt
> 
> This is on upstream commit 0d665e7b109d512b7cae3ccef6e8654714887844.
> Also attaching my config just in case.
> 


View attachment "sg_syzk_next_cbd.c" of type "text/x-csrc" (1581 bytes)