5.15-stable review patch. If anyone has any objections, please let me know.
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From: Olivier Gayot olivier.gayot@canonical.com
commit e06472bab2a5393430cc2fbc3211cd3602422c1e upstream.
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.
This way has broken pyudev utility[1], fixes it by using a mask of 7 bits instead of 8 bits before calling isprint.
Link: https://github.com/pyudev/pyudev/issues/490#issuecomment-2685794648 [1] Link: https://lore.kernel.org/linux-block/4cac90c2-e414-4ebb-ae62-2a4589d9dc6e@can... Cc: Mulhern amulhern@redhat.com Cc: Davidlohr Bueso dave@stgolabs.net Cc: stable@vger.kernel.org Signed-off-by: Olivier Gayot olivier.gayot@canonical.com Signed-off-by: Ming Lei ming.lei@redhat.com Link: https://lore.kernel.org/r/20250305022154.3903128-1-ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- block/partitions/efi.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/block/partitions/efi.c +++ b/block/partitions/efi.c @@ -682,7 +682,7 @@ static void utf16_le_to_7bit(const __le1 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 = '!';