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Date: Sat, 26 May 2018 20:58:58 +0300
From: Alexey Dobriyan <>
To: Salvatore Mesoraca <>
Cc: Kernel Hardening <>,,,, Andrew Morton <>,
	Akinobu Mita <>,
	Dmitry Vyukov <>, Arnd Bergmann <>,
	Davidlohr Bueso <>,
	Kees Cook <>
Subject: Re: [PATCH] proc: prevent a task from writing on its own /proc/*/mem

On Sat, May 26, 2018 at 07:30:47PM +0200, Salvatore Mesoraca wrote:
> 2018-05-26 17:48 GMT+02:00 Alexey Dobriyan <>:
> > 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()
> No, because that hook is skipped when mm == current->mm:


> > or security_file_open()
> This is true, but it looks a bit overkill to me, especially since many of
> the macros/functions used to handle proc's files won't be in scope
> for an external LSM.
> Is there any particular reason why you prefer it done via LSM?

Well, it exists to implement all kinds of non-standard restrictions.

You're probably blacklisting mprotect() and worry that compromised
program might use /proc/self/mem instead. But you need to blacklist
much more that mprotect(). I think forking a dummy "worker" process
to open your /proc/*/mem and pass a descriptor back should still work
with your patch.

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