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Date: Thu, 21 May 2015 11:31:31 -0400 (EDT)
From: cve-assign@...re.org
To: wmealing@...hat.com
Cc: cve-assign@...re.org, oss-security@...ts.openwall.com
Subject: Re: CVE request for vhost/scsi possible memory corruption.

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> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=59c816c1f24df0204e01851431d3bab3eb76719c
> 
> -- vhost/scsi: potential memory corruption
> This code in vhost_scsi_make_tpg() is confusing because we limit "tpgt"
> to UINT_MAX but the data type of "tpg->tport_tpgt" and that is a u16.
> 
> I looked at the context and it turns out that in
> vhost_scsi_set_endpoint(), "tpg->tport_tpgt" is used as an offset into
> the vs_tpg[] array which has VHOST_SCSI_MAX_TARGET (256) elements so
> anything higher than 255 then it is invalid.  I have made that the limit
> now.
> 
> In vhost_scsi_send_evt() we mask away values higher than 255, but now
> that the limit has changed, we don't need the mask.
> --
> The first check that slips past is here:
> 
> -- drivers/vhost/scsi.c - vhost_scsi_make_tpg()
> 
>  if (vs->vs_tpg && vs->vs_tpg[tpg->tport_tpgt])
> 
> My theory is that the possible memory corruption happens later:
> 
> -- drivers/vhost/scsi.c - vhost_scsi_make_tpg()
> 
>   // sets this null pointer, to "tpg" value.
>   vs_tpg[tpg->tport_tpgt] = tpg;
> 
> When vs_tpg[tpg->tport_tpgt] = 0

Nobody else has offered an alternative theory or shown that it is
unexploitable, so probably a CVE ID is reasonable. Use CVE-2015-4036.

- -- 
CVE assignment team, MITRE CVE Numbering Authority
M/S M300
202 Burlington Road, Bedford, MA 01730 USA
[ PGP key available through http://cve.mitre.org/cve/request_id.html ]
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