linux-kernel - Re: Repost: Missing security_mmap_file() in remap_file

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Message-ID: <20190325174703.5cxfgif3z7gdfqhu@kshutemo-mobl1>
Date:   Mon, 25 Mar 2019 20:47:03 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     TongZhang <ztong@...edu>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-security-module@...r.kernel.org, akpm@...ux-foundation.org,
        mhocko@...e.com, dan.j.williams@...el.com, rientjes@...gle.com,
        aarcange@...hat.com, dave@...olabs.net,
        kirill.shutemov@...ux.intel.com,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Shen Wenbo <shenwenbosmile@...il.com>
Subject: Re: Repost: Missing security_mmap_file() in remap_file_pages syscall

On Mon, Mar 25, 2019 at 01:33:51PM -0400, TongZhang wrote:
> Dear Kernel Developers,
> 
> We’d like to bring this up for a discussion again.
> 
> Several months ago we posted an email discussing a case where remap_file_pages() has no security_mmap_file() check.
> At that time we were told that do_mmap_pgoff() will base the new VMA permission on the old one.
> But somehow we still think the check is needed, for the reason that the advisory could first do a 
> mmap() which can pass SELinux check then remap using a completely different file or region of file,
> which could possibly pose a risk.

Could you elabarote on the risk you see? A bad scenario that could be
prevented with SELinux check would be helpful.

-- 
 Kirill A. Shutemov