Re: [PATCH V3] block: fix conversion of GPT partition name to 7-bit
From: Ben Hutchings <hidden>
Date: 2025-03-27 22:34:46
Also in:
linux-efi, stable
On Wed, 2025-03-05 at 10:21 +0800, Ming Lei wrote:
From: Olivier Gayot <redacted> 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.
[...]
quoted hunk ↗ jump to hunk
--- 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.
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