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Date:   Mon, 5 Mar 2018 16:07:10 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     linux-kernel@...r.kernel.org, yeohc@....ibm.com, jann@...jh.net
Subject: Re: [PATCH] mm: relax ptrace mode in process_vm_readv(2)

On Sat, 3 Mar 2018 23:11:16 +0300 Alexey Dobriyan <adobriyan@...il.com> wrote:

> It is more natural to check for read-from-memory permissions in case of
> process_vm_readv() as PTRACE_MODE_ATTACH is equivalent to write
> permissions.
> 
> ...
>
> --- a/mm/process_vm_access.c
> +++ b/mm/process_vm_access.c
> @@ -204,7 +204,7 @@ static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
>  		goto free_proc_pages;
>  	}
>  
> -	mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
> +	mm = mm_access(task, vm_write ? PTRACE_MODE_ATTACH_REALCREDS : PTRACE_MODE_READ_REALCREDS);
>  	if (!mm || IS_ERR(mm)) {
>  		rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
>  		/*

But what is the risk of breaking existing userspace?

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