linux-kernel - Re: NULL deref around blkmq in v4.0-rc1

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Date:	Thu, 9 Apr 2015 14:37:48 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Jan Engelhardt <jengelh@...i.de>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: NULL deref around blkmq in v4.0-rc1–rc7

On Thu, Apr 9, 2015 at 2:25 PM, Jens Axboe <axboe@...nel.dk> wrote:
>
> Not sure why it isn't all zeroed, definitely the saner thing to do at init
> time.

So practically speaking, it might well often be zeroed just because
the BIOS may have initialized memory that way (and big multi-page
allocations have probably not gotten re-used).

> And if this is mpt, we recently ran into some list corruption issues due to
> a bug in the driver. It hit on reboot, but it was scan related, so could be
> a boot issue as well.

So one of the earlier emails had this:

   Copyright (c) 1999-2008 LSI Corporation
   Fusion MPT SAS Host driver 3.04.20
   mptbase: ioc0: Initiating bringup
   ioc0: LSISAS1068 A0: Capabilities={Initiator}
   scsi host0: ioc0: LSISAS1068 A0, FwRev=00000000h, Ports=8, MaxQ=256, IRQ=22
   mptsas: ioc0: attaching ssp device: fw_channel 0, fw_id 1, phy 1,
sas_addr 0x1060504030201a0
   scsi 0:0:0:0: Direct-Access     VBOX     HARDDISK         1.0  PQ: 0 ANSI: 5
   scsi 0:0:0:0: Attached scsi generic sg0 type 0
   mptbase: ioc1: Initiating bringup
   ioc1: LSISAS1068 A0: Capabilities={Initiator}
   scsi host1: ioc1: LSISAS1068 A0, FwRev=00000000h, Ports=8, MaxQ=256, IRQ=17
   mptsas: ioc1: attaching ssp device: fw_channel 0, fw_id 0, phy 0,
sas_addr 0x60504030201a0
   scsi 1:0:0:0: Direct-Access     VBOX     HARDDISK         1.0  PQ: 0 ANSI: 5
   scsi 1:0:0:0: Attached scsi generic sg1 type 0

and I'm assuming that that is the backing storage.

And yes, memory corruption sounds like a more likely cause than
anything else. I don't like how the request data wasn't fully
initialized, but the cmd->sense_buffer pointer itself *should* have
been initialized by the ->init_request() call.

So I don't actually expect my patch to really make any difference,
although I do think that code should be looked at.

                            Linus
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