Re: [Libguestfs] [hivex PATCH] lib: write: improve key collation compatibility with Windows

There are multiple problems with using strcasecmp() for ordering registry keys: (1) strcasecmp() is influenced by LC_CTYPE. (2) strcasecmp() cannot implement case conversion for multibyte UTF-8 sequences. (3) Even with LC_CTYPE=POSIX and key names consisting solely of ASCII characters, strcasecmp() converts characters to lowercase, for comparison. But on Windows, the CompareStringOrdinal() function converts characters to uppercase. This makes a difference when comparing a letter to one of the characters that fall between 'Z' (0x5A) and 'a' (0x61), namely {'[', '\\', ']', '^', '_', '`'}. For example, 'c' (0x63) > '_' (0x5F) 'C' (0x43) < '_' (0x5F) Compare key names byte for byte, eliminating problems (1) and (3). Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1648520 Signed-off-by: Laszlo Ersek <lersek(a)redhat.com&gt; --- lib/write.c | 32 +++++++++++++++++++++++++++++++- 1 file changed, 31 insertions(+), 1 deletion(-) diff --git a/lib/write.c b/lib/write.c index 70105c9d9907..d9a13a3c18b6 100644 --- a/lib/write.c +++ b/lib/write.c @@ -462,7 +462,37 @@ compare_name_with_nk_name (hive_h *h, const char *name, hive_node_h nk_offs) return 0; } - int r = strcasecmp (name, nname); + /* Perform a limited case-insensitive comparison. ASCII letters will be + * *upper-cased*. Multibyte sequences will produce nonsensical orderings. + */ + int r = 0; + const char *s1 = name; + const char *s2 = nname; + + for (;;) { + unsigned char c1 = *(s1++); + unsigned char c2 = *(s2++); + + if (c1 >= 'a' && c1 <= 'z') + c1 = 'A' + (c1 - 'a'); + if (c2 >= 'a' && c2 <= 'z') + c2 = 'A' + (c2 - 'a'); + if (c1 < c2) { + /* Also covers the case when "name" is a prefix of "nname". */ + r = -1; + break; + } + if (c1 > c2) { + /* Also covers the case when "nname" is a prefix of "name". */ + r = 1; + break; + } + if (c1 == '\0') { + /* Both strings end. */ + break; + } + } + free (nname); return r;