linux-kernel - Re: [PATCH v2 1/6] uaccess: Add copy_from_user

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Message-Id: <20260112100059.12139-1-fushuai.wang@linux.dev>
Date: Mon, 12 Jan 2026 18:00:59 +0800
From: Fushuai Wang <fushuai.wang@...ux.dev>
To: aliceryhl@...gle.com
Cc: akpm@...ux-foundation.org,
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Subject: Re: [PATCH v2 1/6] uaccess: Add copy_from_user_nul helper

>> From: Fushuai Wang <wangfushuai@...du.com>
>> 
>> Many places call copy_from_user() to copy a buffer from user space,
>> and then manually add a NULL terminator to the destination buffer,
>> e.g.:
>> 
>> 	if (copy_from_user(dest, src, len))
>> 		return -EFAULT;
>> 	dest[len] = '\0';
>> 
>> This is repetitive and error-prone. Add a copy_from_user_nul() helper to
>> simplify such patterns. It copied n bytes from user space to kernel space,
>> and NUL-terminates the destination buffer.
>> 
>> Signed-off-by: Fushuai Wang <wangfushuai@...du.com>
>
> Hmm, this function is very very similar to strncpy_from_user(). Should
> they be using that instead?
> 
> Alice

The strncpy_from_user() is for NUL-terminated strings and stops at the
first NUL in userspace. But copy_from_user_nul() always copies a fixed length
and adds a NUL at the end in kernel space, even if userspace data doesn’t
contain a NUL.

So I think they are for different cases and can’t replace each other.

---
Regards,
WANG