linux-kernel - Re: [Linux-kernel-mentees] [PATCH] scsi/megaraid: Prevent kernel-infoleak in kioc_to

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Message-ID: <20200728105704.GA407553@PWN>
Date:   Tue, 28 Jul 2020 06:57:04 -0400
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Kashyap Desai <kashyap.desai@...adcom.com>,
        Sumit Saxena <sumit.saxena@...adcom.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Shivasharan S <shivasharan.srikanteshwara@...adcom.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        megaraidlinux.pdl@...adcom.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Linux-kernel-mentees] [PATCH] scsi/megaraid: Prevent
 kernel-infoleak in kioc_to_mimd()

On Tue, Jul 28, 2020 at 11:41:37AM +0300, Dan Carpenter wrote:
> On Mon, Jul 27, 2020 at 05:02:35PM -0400, Peilin Ye wrote:
> > hinfo_to_cinfo() does no operation on `cinfo` when `hinfo` is NULL,
> > causing kioc_to_mimd() to copy uninitialized stack memory to userspace.
> > Fix it by initializing `cinfo` with memset().
> 
> But "hinfo" can't be NULL so this patch isn't required.  It's a bit
> hard for Smatch to follow the code.
> 
> We know that "opcode" is 82 so the buffer is allocated by mimd_to_kioc()
> -> mraid_mm_attach_buf().

You are right. mraid_mm_ioctl() returns -ENOMEM and never reaches
kioc_to_mimd() if mraid_mm_attach_buf() failed to get a buffer, so
`hinfo` can never be NULL for kioc_to_mimd().

Next time I will trace the data flow more carefully. Thank you for
pointing this out!

Peilin Ye

> Generally, don't silence static checker warnings unless it makes the
> code more readable.  It's the checker writer's job to fix their own code.
> In this case, that's me, but parsing the code is quite complicated and I
> don't have a plan for how to fix it.
> 
> regards,
> dan carpenter
>