On Thu, 27 Mar 2025 23:34:29 +0100
Ben Hutchings <ben@xxxxxxxxxxxxxxx> wrote:
> 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)))
Given that, for 7-bit ascii, isprint(uc) is equivalent to (uc >= 0x20 && uc <= 0x7e)
you can do:
if (uc >= 0x20 && uc <= 0x7e)
c = uc;
else
c = uc ? '!' : 0;
David
> c = uc;
> else
> c = '!';
>
> Ben.
>
