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Message-ID: <20170512214144.GT390@ZenIV.linux.org.uk>
Date: Fri, 12 May 2017 22:41:44 +0100
From: Al Viro <viro@...IV.linux.org.uk>
To: Kees Cook <keescook@...omium.org>
Cc: Russell King - ARM Linux <linux@...linux.org.uk>,
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Subject: Re: Re: [PATCH v9 1/4] syscalls: Verify address
limit before returning to user-mode
On Fri, May 12, 2017 at 02:17:19PM -0700, Kees Cook wrote:
> Two things are at risk from stack exhaustion: thread_info (mainly
> addr_limit) when on the stack (fixed by THREAD_INFO_IN_TASK), and
Really? Let's take a look at arm, for example:
struct thread_info {
unsigned long flags; /* low level flags */
int preempt_count; /* 0 => preemptable, <0 => bug */
mm_segment_t addr_limit; /* address limit */
struct task_struct *task; /* main task structure */
and current() is defined as current_thread_info()->task.
Seriously, look at these beasts. Overwriting ->addr_limit is nowhere near
the top threat. If attacker can overwrite thread_info, you have lost.
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