linux-kernel - Re: [PATCH 2/3] binder: Prevent repeated use of ->mmap() via NULL mapping

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Sat, 19 Oct 2019 16:07:02 +0200
From:   "Christian Brauner" <christian.brauner@...ntu.com>
To:     "Jann Horn" <jannh@...gle.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        "Todd Kjos" <tkjos@...roid.com>,
        "Martijn Coenen" <maco@...roid.com>,
        "Joel Fernandes" <joel@...lfernandes.org>,
        "Christian Brauner" <christian@...uner.io>, <jannh@...gle.com>
Cc:     <devel@...verdev.osuosl.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] binder: Prevent repeated use of ->mmap() via NULL
 mapping

On Fri Oct 18, 2019 at 10:56 PM Jann Horn wrote:
> binder_alloc_mmap_handler() attempts to detect the use of ->mmap() on a
> binder_proc whose binder_alloc has already been initialized by checking
> whether alloc->buffer is non-zero.
> 
> Before commit 880211667b20 ("binder: remove kernel vm_area for buffer
> space"), alloc->buffer was a kernel mapping address, which is always
> non-zero, but since that commit, it is a userspace mapping address.
> 
> A sufficiently privileged user can map /dev/binder at NULL, tricking
> binder_alloc_mmap_handler() into assuming that the binder_proc has not been
> mapped yet. This leads to memory unsafety.
> Luckily, no context on Android has such privileges, and on a typical Linux
> desktop system, you need to be root to do that.
> 
> Fix it by using the mapping size instead of the mapping address to
> distinguish the mapped case. A valid VMA can't have size zero.
> 
> Fixes: 880211667b20 ("binder: remove kernel vm_area for buffer space")
> Cc: stable@...r.kernel.org
> Signed-off-by: Jann Horn <jannh@...gle.com>

Acked-by: Christian Brauner <christian.brauner@...ntu.com>