linux-kernel - Re: [PATCH] Fix problem with size of allocation in libsas

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Date:	Sun, 11 Nov 2007 19:33:43 -0500
From:	Douglas Gilbert <dougg@...que.net>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
CC:	Jesper Juhl <jesper.juhl@...il.com>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Fix problem with size of allocation in libsas

James Bottomley wrote:
> On Mon, 2007-11-12 at 00:24 +0100, Jesper Juhl wrote:
>> From: Jesper Juhl <jesper.juhl@...il.com>
>>
>> in sas_get_phy_change_count(), the line
>> 	disc_resp = alloc_smp_resp(DISCOVER_RESP_SIZE);
>> will allocate 56 bytes due to this define:
>> 	#define DISCOVER_RESP_SIZE 56
>> But, the struct is actually 60 bytes in size.
>>
>> So change the define to be 
>> 	#define DISCOVER_RESP_SIZE sizeof(struct smp_resp)
>> so we always get the correct size even when people 
>> fiddle with the structure.
>>
>> This change also fixes the same problem in 
>> sas_get_phy_attached_sas_addr()
>>
>> (Found by the Coverity checker. Compile tested only)
> 
> Well, your fix is definitely wrong.
> 
> Could you explain the problem a little more?  The discover response SMP
> frame is 56 bytes as mandated by the standard.  I don't see anywhere in
> the code where we're actually using a value beyond the 56th byte ...
> where is the problem use?

The response size of SMP DISCOVER keeps growing with
each rev. Currently in SAS-2 revision 12 it is 112 bytes long!
The original SAS standard and SAS 1.1 have implicit response
sizes and for DISCOVER that is 56 bytes.

To be compliant with SAS-2 the code should read byte 3 of
a DISCOVER response. If it is zero then the response length
is 56 bytes, otherwise the response length is that many
dwords (i.e. 4 byte units) plus 4 bytes for the CRC.
[Similar logic applies to many other SMP responses.]

I have tables for all SMP requests and response (up until
SAS-2 rev 12) in my smp_utils package, see the smp_lib.c
file.

Doug Gilbert
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