linux-kernel - Re: [PATCH -mm 1/1] ptrace: PTRACE_GETFDPIC: fix the unsafe usage of child->mm

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Message-ID: <AANLkTilT3D8c86LYK2DxcNpM2F3D8iCbgY_sfUg8h58p@mail.gmail.com>
Date:	Tue, 25 May 2010 13:28:19 -0400
From:	Mike Frysinger <vapier.adi@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	David Howells <dhowells@...hat.com>,
	Roland McGrath <roland@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-sh@...r.kernel.org, Paul Mundt <lethal@...ux-sh.org>,
	uclinux-dist-devel@...ckfin.uclinux.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm 1/1] ptrace: PTRACE_GETFDPIC: fix the unsafe usage of 
	child->mm

On Tue, May 25, 2010 at 06:23, Oleg Nesterov wrote:
>        - arch/blackfin/kernel/ptrace.c:is_user_addr_valid()
>          needs mmap_sem around find_vma()
>
>          The lockless access to mm->context.sram_list doesn't look
>          safe to me.
>
>          If we add get_task_mm() - this protects us against
>          destroy_context() only. What is the tracee's sub-thread
>          does sys_sram_alloc() or sys_sram_free() in parallel?

i dont believe there are any code paths in UP systems where this would
be a practical problem because sram_list is only updated by syscalls
from userspace.  we probably should add proper locking to this
structure though.  i'll open a tracker item about it, thanks !
-mike
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