On Tue, May 23, 2023 at 6:53 AM Olivier Gayot
<olivier.gayot@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> ---
> 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
