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

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Date:	Mon, 12 Nov 2007 01:13:33 +0100
From:	"Jesper Juhl" <jesper.juhl@...il.com>
To:	"James Bottomley" <James.Bottomley@...senpartnership.com>
Cc:	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

On 12/11/2007, James Bottomley <James.Bottomley@...senpartnership.com> 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?
>

I haven't found any actual problem *use*, I just looked at the size of
'struct smp_resp' and noticed that coverity seemed to be right that 56
bytes are not sufficient to hold the members of the struct.  There are
32 bytes in the first members + the union and I don't see how that can
ever stay at 56 bytes...?  So, we are allocating memory and storing it
in a 'struct smp_resp *', but we are allocating less than
sizeof(smp_resp) - how is that not a (potential) problem?

-- 
Jesper Juhl <jesper.juhl@...il.com>
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