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@canonical.com/
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>
30f67c1048