linux-kernel - Re: [PATCH 3/3] sysctl: detect overflows when converting to int

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Date:	Tue, 31 Mar 2015 15:45:54 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Heinrich Schuchardt <xypron.glpk@....de>
Cc:	Michal Nazarewicz <mina86@...a86.com>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Joe Perches <joe@...ches.com>, Josh Hunt <johunt@...mai.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Daniel Walter <dwalter@...gle.com>,
	David Rientjes <rientjes@...gle.com>,
	Kees Cook <keescook@...omium.org>,
	"David S. Miller" <davem@...emloft.net>,
	Johannes Weiner <hannes@...xchg.org>,
	Aaron Tomlin <atomlin@...hat.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Eric B Munson <emunson@...mai.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Sam Ravnborg <sam@...nborg.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] sysctl: detect overflows when converting to int

On Sun, 29 Mar 2015 21:28:29 +0200 Heinrich Schuchardt <xypron.glpk@....de> wrote:

> When converting unsigned long to int overflows may occur.
> These currently are not detected when writing to the sysctl
> file system.
> 
> E.g. on a system where int has 32 bits and long has 64 bits
>   echo 0x800001234 > /proc/sys/kernel/threads-max
> has the same effect as
>   echo 0x1234 > /proc/sys/kernel/threads-max
> 
> The patch adds the missing check in do_proc_dointvec_conv.
> 
> With the patch an overflow will result in an error EINVAL when
> writing to the the sysctl file system.

hm, why fix this?  There's a small risk of breaking
accidentally-working userspace, but I expect we can live with that.

But how big a problem is this, really?  This behaviour is quite
expected, after all.

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