linux-kernel - Re: [PATCH 1/5] ptrace: don't modify flags on PTRACE

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Message-ID: <20120210171703.GA8908@redhat.com>
Date:	Fri, 10 Feb 2012 18:17:03 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Pedro Alves <palves@...hat.com>,
	Jan Kratochvil <jan.kratochvil@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] ptrace: don't modify flags on PTRACE_SETOPTIONS
	failure

On 02/10, Denys Vlasenko wrote:

> On ptrace(PTRACE_SETOPTIONS, pid, 0, <opts>), we used to set
> those option bits which are known, and then fail with -EINVAL
> if there are some unknown bits in <opts>.
> 
> This in inconsistent with typical error handling, which
> does not change any state if input is invalid.
> 
> This patch changes PTRACE_SETOPTIONS behavior so that
> in this case, we return -EINVAL and don't change any bits
> in task->ptrace.
> 
> It's very unlikely that there is userspace code in the wild which
> will be affected by this change: it should have the form
> 
>     ptrace(PTRACE_SETOPTIONS, pid, 0, PTRACE_O_BOGUSOPT)
> 
> where PTRACE_O_BOGUSOPT is a constant unknown to the kernel.
> But kernel headers, naturally, don't contain any
> PTRACE_O_BOGUSOPTs, thus the only way userspace can use one
> if it defines one itself. I can't see why anyone would do such
> a thing deliberately.
> 
> Signed-off-by: Denys Vlasenko <vda.linux@...glemail.com>
> Acked-by: Tejun Heo <tj@...nel.org>

Reviewed-by: Oleg Nesterov <oleg@...hat.com>

> ---
>  kernel/ptrace.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index 00ab2ca..273f56e 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -528,6 +528,9 @@ int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long ds
>  
>  static int ptrace_setoptions(struct task_struct *child, unsigned long data)
>  {
> +	if (data & ~(unsigned long)PTRACE_O_MASK)
> +		return -EINVAL;
> +
>  	child->ptrace &= ~PT_TRACE_MASK;
>  
>  	if (data & PTRACE_O_TRACESYSGOOD)
> @@ -551,7 +554,7 @@ static int ptrace_setoptions(struct task_struct *child, unsigned long data)
>  	if (data & PTRACE_O_TRACEEXIT)
>  		child->ptrace |= PT_TRACE_EXIT;
>  
> -	return (data & ~PTRACE_O_MASK) ? -EINVAL : 0;
> +	return 0;
>  }
>  
>  static int ptrace_getsiginfo(struct task_struct *child, siginfo_t *info)
> -- 
> 1.7.7.6
> 

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