linux-kernel - Re: [Security] [PATCH] xtensa: prevent arbitrary read in ptrace

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Message-ID: <4E175A8B.2040007@zankel.net>
Date:	Fri, 08 Jul 2011 12:29:15 -0700
From:	Chris Zankel <qvadiz@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Rosenberg <drosenberg@...curity.com>, security@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [Security] [PATCH] xtensa: prevent arbitrary read in ptrace

Hi,

I'll try to run a build this weekend and will look if that code builds 
at all.

Thanks,
-Chris


On 7/8/11 11:42 AM, Oleg Nesterov wrote:
> On 07/08, Andrew Morton wrote:
>>
>> On Thu, 07 Jul 2011 20:03:54 -0400
>> Dan Rosenberg<drosenberg@...curity.com>  wrote:
>>
>>> Prevent an arbitrary kernel read. Check the user pointer with
>>> access_ok() before copying data in.
>>>
>>> Signed-off-by: Dan Rosenberg<drosenberg@...curity.com>
>>> Cc: stable@...nel.org
>>> ---
>>>   arch/xtensa/kernel/ptrace.c |    3 +++
>>>   1 files changed, 3 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/arch/xtensa/kernel/ptrace.c b/arch/xtensa/kernel/ptrace.c
>>> index c72c947..ddce75e 100644
>>> --- a/arch/xtensa/kernel/ptrace.c
>>> +++ b/arch/xtensa/kernel/ptrace.c
>>> @@ -147,6 +147,9 @@ int ptrace_setxregs(struct task_struct *child, void __user *uregs)
>>>   	elf_xtregs_t *xtregs = uregs;
>>>   	int ret = 0;
>>>
>>> +	if (!access_ok(VERIFY_READ, uregs, sizeof(elf_xtregs_t)))
>>> +		return -EIO;
>>
>> This should be -EFAULT, methinks?
>
> Also, it seems that ptrace_setxregs/ptrace_getxregs could be static?
>
> The patch looks "obviously correct" but I don't understand this code.
>
> Hmm. We don't read/write the XTENSA_HAVE_COPROCESSORS data, but use
> sizeof(elf_xtregs_t) anyway. This looks a bit strange but I guess
> this doesn't matter.
>
> Oleg.
>

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