Re: NULL deref around blkmq in v4.0-rc1ârc7

From: Jan Engelhardt
Date: Thu Apr 09 2015 - 18:32:56 EST

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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