Re: [PATCH v2 1/6] uaccess: Add copy_from_user_nul helper

[Yury Norov]

On Tue, Jan 13, 2026 at 01:00:25PM -0500, Yury Norov wrote:
> On Mon, Jan 12, 2026 at 03:30:34PM +0800, Fushuai Wang wrote:
> > From: Fushuai Wang <wangfushuai@xxxxxxxxx>
> > 
> > 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.:
> 
> 6 is not many
> 
> > 
> > 	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@xxxxxxxxx>
> 
> I checked the cases you've found, and all them clearly abuse
> copy_from_user(). For example, #2 in tlbflush_write_file():
> 
>         if (copy_from_user(buf, user_buf, len))
>                 return -EFAULT;
> 
>         buf[len] = '\0';
>         if (kstrtoint(buf, 0, &ceiling))
>                 return -EINVAL;
> 
> should be:
>         
>         len = strncpy_from_user(buf, user_buf, len);
>         if (len < 0)
>                 return len;
> 
>         ret = kstrtoint(buf, 0, &ceiling);
>         if (ret)
>                 return ret;
> 
> See, if you use the right API, you don't need this weird
> copy_from_user_nul(). Also notice how nice the original version hides
> possible ERANGE in kstrtoint().

Huh, we actually already have kstrtoint_from_user, so this should be a
one-liner.