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

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Date:   Mon, 25 Mar 2019 13:33:51 -0400
From:   TongZhang <ztong@...edu>
To:     LKML <linux-kernel@...r.kernel.org>,
        linux-security-module@...r.kernel.org
Cc:     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: Repost: Missing security_mmap_file() in remap_file_pages syscall 

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.

Thanks,
- Tong

The original post is pasted below:

8<—————————————————————————————
[1.] One line summary of the problem:

Possible missing security_mmap_file() in remap_file_pages

[2.] Full description of the problem/report:

We noticed remap_file_pages syscall uses do_mmap_pgoff without LSM check: security_mmap_file().

This system call passed user controllable parameters to do_mmap_pgoff().

We think that this LSM check should be added in order to be consistent with other cases,
for example:
in system call mmap_pgoff(), shmat(), they all have security_mmap_file() check before calling
do_mmap_pgoff().

[3.] Keywords: LSM check
[4.] Kernel information
[4.1] Kernel Version: 4.14.61

8<—————————————————————————————