efi_loader: Fix buffer underflow

If the array index 'i' < 128, the 'codepage' array is accessed using
[-128...-1] in efi_unicode_collation.c:262. This can lead to a buffer
overflow.

    Negative index in efi_unicode_collation.c:262.

The index of the 'codepage' array should be c - 0x80 instead of i - 0x80.

Fixes: 0bc4b0da7b59 ("efi_loader: EFI_UNICODE_COLLATION_PROTOCOL")
Signed-off-by: Mikhail Ilin <ilin.mikhail.ol@gmail.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

diff --git a/lib/efi_loader/efi_unicode_collation.c b/lib/efi_loader/efi_unicode_collation.c
index 36be798..c4c7572 100644 (file)
--- a/lib/efi_loader/efi_unicode_collation.c
+++ b/lib/efi_loader/efi_unicode_collation.c
@@ -257,7 +257,7 @@ static void EFIAPI efi_fat_to_str(struct efi_unicode_collation_protocol *this,
        for (i = 0; i < fat_size; ++i) {
                c = (unsigned char)fat[i];
                if (c > 0x80)
-                       c = codepage[i - 0x80];
+                       c = codepage[c - 0x80];
                string[i] = c;
                if (!c)
                        break;