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

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Message-ID: <alpine.LSU.2.20.1504100030270.14912@nerf40.vanv.qr>
Date:	Fri, 10 Apr 2015 00:32:50 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...i.de>
To:	Jens Axboe <axboe@...nel.dk>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"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 Thursday 2015-04-09 23:42, Jens Axboe wrote:
>
>> So I don't actually expect my patch to really make any difference,
>> although I do think that code should be looked at.
>
> Jan, is it always clearing in a page size? That seems odd, especially if we're
> considering random gunk in memory.

The particular memset in scsi_init_cmd_errh would only clear
SCSI_SENSE_BUFFERSIZE. The problem really was that cmd->sense_buffer
was nonsensical (I did a hexdump) and read 0x1000. In one instance,
it even read 0x10000 because I used that value in an if clause
preceding a printk statement I added. Together with __GFP_ZERO
apparently fixing the issue for today, the noninitialized memory
theory looks like the most applicable one to me currently.
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