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Date:   Sat, 26 May 2018 18:48:19 +0300
From:   Alexey Dobriyan <adobriyan@gmail.com>
To:     Salvatore Mesoraca <s.mesoraca16@gmail.com>
Cc:     kernel-hardening@lists.openwall.com,
        linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Akinobu Mita <akinobu.mita@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH] proc: prevent a task from writing on its own /proc/*/mem
Message-ID: <20180526154819.GA14016@avx2>
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On Sat, May 26, 2018 at 04:50:46PM +0200, Salvatore Mesoraca wrote:
> Prevent a task from opening, in "write" mode, any /proc/*/mem
> file that operates on the task's mm.
> /proc/*/mem is mainly a debugging means and, as such, it shouldn't
> be used by the inspected process itself.
> Current implementation always allow a task to access its own
> /proc/*/mem file.
> A process can use it to overwrite read-only memory, making
> pointless the use of security_file_mprotect() or other ways to
> enforce RO memory.

You can do it in security_ptrace_access_check() or security_file_open()