On Wed, 2025-03-05 at 10:21 +0800, Ming Lei wrote:
> From: Olivier Gayot <olivier.gayot@xxxxxxxxxxxxx>
>
> 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 "!"
Also any character with low 8 bits equal to 0 terminates the string.
> 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.
Indeed. But this change seems to make it worse!
[...]
> 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.
[...]
> --- 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 = '!';
Now we map 'é' to 'i' and '€' to ','. Didn't we want to map them to
'!'?
We shouldn't mask the input character; instead we should do a range
check before calling isprint(). Something like:
u16 uc = le16_to_cpu(in[i]);
u8 c;
if (uc < 0x80 && (uc == 0 || isprint(uc)))
c = uc;
else
c = '!';
Ben.
--
Ben Hutchings
If God had intended Man to program,
we'd have been born with serial I/O ports.
Attachment:
signature.asc
Description: This is a digitally signed message part
