linux-kernel - Re: yama_ptrace_access_check(): possible recursive locking detected

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Message-ID: <20120815181711.GA19018@redhat.com>
Date:	Wed, 15 Aug 2012 20:17:11 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Fengguang Wu <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: yama_ptrace_access_check(): possible recursive locking detected

On 08/15, Kees Cook wrote:
>
> It sounds like get_task_comm shouldn't have locking at all then? It
> should just do a length-limited copy

Without task_lock() get_task_comm() can copy incomplete new name.

Honestly, I do not know any user which "strictly" needs the correct
name. may be proc.

> and make sure there is a trailing
> 0-byte?

get_task_comm()->strncpy() should always see (and copy) 0-byte.
comm[TASK_COMM_LEN - 1] == '\0' and this byte is never changed.

set_task_comm()->strlcpy() can write to this byte, but it can
only write 0 again.

Or I am totally confused ;)

Oleg.

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