linux-kernel - Re: [PATCH] scsi: megaraid_sas: fix a missing-check bug

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Date:   Mon, 15 Oct 2018 23:43:12 -0400
From:   "Martin K. Petersen" <martin.petersen@...cle.com>
To:     Wenwen Wang <wang6495@....edu>
Cc:     Kangjie Lu <kjlu@....edu>,
        Kashyap Desai <kashyap.desai@...adcom.com>,
        Sumit Saxena <sumit.saxena@...adcom.com>,
        Shivasharan S <shivasharan.srikanteshwara@...adcom.com>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        megaraidlinux.pdl@...adcom.com (open list:MEGARAID SCSI/SAS DRIVERS),
        linux-scsi@...r.kernel.org (open list:MEGARAID SCSI/SAS DRIVERS),
        linux-kernel@...r.kernel.org (open list)
Subject: Re: [PATCH] scsi: megaraid_sas: fix a missing-check bug


Wenwen,

> In megasas_mgmt_compat_ioctl_fw(), to handle the structure
> compat_megasas_iocpacket 'cioc', a user-space structure megasas_iocpacket
> 'ioc' is allocated before megasas_mgmt_ioctl_fw() is invoked to handle the
> packet. Since the two data structures have different fields, the data is
> copied from 'cioc' to 'ioc' field by field. In the copy process,
> 'sense_ptr' is prepared if the field 'sense_len' is not null, because it
> will be used in megasas_mgmt_ioctl_fw(). To prepare 'sense_ptr', the
> user-space data 'ioc->sense_off' and 'cioc->sense_off' are copied and saved
> to kernel-space variables 'local_sense_off' and 'user_sense_off'
> respectively. Given that 'ioc->sense_off' is also copied from
> 'cioc->sense_off', 'local_sense_off' and 'user_sense_off' should have the
> same value. However, 'cioc' is in the user space and a malicious user can
> race to change the value of 'cioc->sense_off' after it is copied to
> 'ioc->sense_off' but before it is copied to 'user_sense_off'. By doing so,
> the attacker can inject different values into 'local_sense_off' and
> 'user_sense_off'. This can cause undefined behavior in the following
> execution, because the two variables are supposed to be same.
>
> This patch enforces a check on the two kernel variables 'local_sense_off'
> and 'user_sense_off' to make sure they are the same after the copy. In case
> they are not, an error code EINVAL will be returned.

Broadcom folks: Please review!

-- 
Martin K. Petersen	Oracle Linux Engineering