linux-kernel - RE: Using memcpy instead of copy_to

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Message-ID: <55b4da35b6e44bf48306280d900e0fa8@AcuMS.aculab.com>
Date:   Tue, 25 Jan 2022 22:21:31 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Aleksey Senin' <aleksey-linux-kernel@...in.name>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: Using memcpy instead of copy_to_user. xprtrdma code.

From: Aleksey Senin <aleksey-linux-kernel@...in.name>
> Sent: 25 January 2022 18:04
> 
> This specific patch -  - implements using memcpy instead of
> copy_to_user. Why is it considered to be safe in this specific case?
> All readings about how to copy data are mentioning to use
> copy_to_user/copy_from_user. Why use direct copy here? What prevents
> the kernel from failure if the page is not present or doesn't have
> required access rights?
> 
> @@ -103,8 +102,8 @@ static int read_reset_stat(struct ctl_table
> *table, int write,
>                 len -= *ppos;
>                 if (len > *lenp)
>                         len = *lenp;
> -               if (len && copy_to_user(buffer, str_buf, len))
> -                       return -EFAULT;
> +               if (len)
> +                       memcpy(buffer, str_buf, len);
> 
> Reference to the specific patch in the services of commits:
> https://lkml.org/lkml/2020/4/17/60

Read the commit message.

> 
> Commit itself:
> 32927393dc1ccd60fb2bdc05b9e8e88753761469

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