linux-kernel - Re: [PATCH 1/1] block: fix conversion of GPT partition name to 7-bit

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Message-ID: <CAFj5m9JEDW0kLfnDhF4xNFzMTpHBH6Xpdb+XVLf73oq3vzCjQg@mail.gmail.com>
Date: Sat, 1 Mar 2025 09:26:35 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Olivier Gayot <olivier.gayot@...onical.com>
Cc: linux-kernel@...r.kernel.org, 
	Daniel Bungert <daniel.bungert@...onical.com>, linux-block <linux-block@...r.kernel.org>
Subject: Re: [PATCH 1/1] block: fix conversion of GPT partition name to 7-bit

On Tue, May 23, 2023 at 6:53 AM Olivier Gayot
<olivier.gayot@...onical.com> wrote:
>
> The utf16_le_to_7bit function claims to, naively, convert a UTF-16
> string to a 7-bit ASCII string. By naively, we mean that it:
>  * drops the first byte of every character in the original UTF-16 string
>  * checks if all characters are printable, and otherwise replaces them
>    by exclamation mark "!".
>
> This means that theoretically, all characters outside the 7-bit ASCII
> range should be replaced by another character. Examples:
>
>  * lower-case alpha (ɒ) 0x0252 becomes 0x52 (R)
>  * ligature OE (œ) 0x0153 becomes 0x53 (S)
>  * hangul letter pieup (ㅂ) 0x3142 becomes 0x42 (B)
>  * upper-case gamma (Ɣ) 0x0194 becomes 0x94 (not printable) so gets
>    replaced by "!"
>
> The result of this conversion for the GPT partition name is passed to
> user-space as PARTNAME via udev, which is confusing and feels questionable.
>
> However, there is a flaw in the conversion function itself. By dropping
> one byte of each character and using isprint() to check if the remaining
> byte corresponds to a printable character, we do not actually guarantee
> that the resulting character is 7-bit ASCII.
>
> This happens because we pass 8-bit characters to isprint(), which
> in the kernel returns 1 for many values > 0x7f - as defined in ctype.c.
>
> This results in many values which should be replaced by "!" to be kept
> as-is, despite not being valid 7-bit ASCII. Examples:
>
>  * e with acute accent (é) 0x00E9 becomes 0xE9 - kept as-is because
>    isprint(0xE9) returns 1.
>  * euro sign (€) 0x20AC becomes 0xAC - kept as-is because isprint(0xAC)
>    returns 1.
>
> Fixed by using a mask of 7 bits instead of 8 bits before calling
> isprint.
>
> Signed-off-by: Olivier Gayot <olivier.gayot@...onical.com>
> ---
>  block/partitions/efi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/block/partitions/efi.c b/block/partitions/efi.c
> index 5e9be13a56a8..7acba66eed48 100644
> --- a/block/partitions/efi.c
> +++ b/block/partitions/efi.c
> @@ -682,7 +682,7 @@ static void utf16_le_to_7bit(const __le16 *in, unsigned int size, u8 *out)
>         out[size] = 0;
>
>         while (i < size) {
> -               u8 c = le16_to_cpu(in[i]) & 0xff;
> +               u8 c = le16_to_cpu(in[i]) & 0x7f;
>
>                 if (c && !isprint(c))
>                         c = '!';

Hello Olivier,

Looks like you didn't Cc linux-block maillist and Jens, can you
re-send the patch to
linux-block for review?

Thanks,
Ming