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Re: [PATCH] vfprint: validate nargs and argument-based offsets
- From: Tomas Hoger <thoger at redhat dot com>
- To: Kees Cook <kees at outflux dot net>
- Cc: Andreas Jaeger <aj at suse dot com>, "Ryan S. Arnold" <ryan dot arnold at gmail dot com>, libc-alpha at sourceware dot org, Paul Eggert <eggert at cs dot ucla dot edu>, Roland McGrath<roland at hack dot frob dot com>, Andreas Schwab <schwab at linux-m68k dot org>
- Date: Mon, 5 Mar 2012 18:09:23 +0100
- Subject: Re: [PATCH] vfprint: validate nargs and argument-based offsets
- References: <20120302185346.GE3990@outflux.net>
On Fri, 2 Mar 2012 10:53:46 -0800 Kees Cook wrote:
> The nargs value can overflow when doing allocations, allowing
> arbitrary memory writes via format strings, bypassing _FORTIFY_SOURCE:
> This checks for nargs overflow and possibly allocates from heap
> instead of stack, and adds a regression test for the situation.
A commenter in Red Hat bugzilla proposed different fix:
The easiest fix would have been to restrict "nargs" to NL_ARGMAX.
which has the benefit of avoiding possibly large heap allocation in the
bad case. Kees, have you considered such approach?