libblkid: iso9660: improve label parsing

Label in Joliet is UNICODE (UTF16BE) but can contain only 16 characters.
Label in PVD is subset of ASCII but can contain up to the 32 characters.
Non-representable characters are stored as replacement character '_'.

Label in Joliet is in most cases trimmed but UNICODE version of label in
PVD. Based on these facts try to reconstruct original label if label in
Joliet is prefix of the label in PVD (ignoring non-representable
characters).

It is possible that label in Joliet and PVD are totally different. In this
case label from Joliet as prior this change.

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>

diff --git a/libblkid/src/superblocks/iso9660.c b/libblkid/src/superblocks/iso9660.c
index 1a296e217de9101108950c5ca5d6db14574e83c8..52bf6523efe973d3b1c3be043bf66863ff0dc8ac 100644 (file)
--- a/libblkid/src/superblocks/iso9660.c
+++ b/libblkid/src/superblocks/iso9660.c
@@ -19,6 +19,7 @@
 #include <ctype.h>
 
 #include "superblocks.h"
+#include "cctype.h"
 
 struct iso9660_date {
        unsigned char year[4];
@@ -79,20 +80,6 @@ struct high_sierra_volume_descriptor {
        unsigned char   volume_id[32];
 } __attribute__((packed));
 
-/* returns 1 if the begin of @ascii is equal to @utf16 string.
- */
-static int ascii_eq_utf16be(unsigned char *ascii,
-                       unsigned char *utf16, size_t len)
-{
-       size_t a, u;
-
-       for (a = 0, u = 0; u < len; a++, u += 2) {
-               if (utf16[u] != 0x0 || ascii[a] != utf16[u + 1])
-                       return 0;
-       }
-       return 1;
-}
-
 /* old High Sierra format */
 static int probe_iso9660_hsfs(blkid_probe pr, const struct blkid_idmag *mag)
 {
@@ -166,12 +153,51 @@ static int is_str_empty(const unsigned char *str, size_t len)
        return 1;
 }
 
+/* if @utf16 is prefix of @ascii (ignoring non-representable characters and upper-case conversion)
+ * then reconstruct prefix from @utf16 and @ascii, append suffix from @ascii, fill it into @out
+ * and returns length of bytes written into @out; otherwise returns zero */
+static size_t merge_utf16be_ascii(unsigned char *out, const unsigned char *utf16, const unsigned char *ascii, size_t len)
+{
+       size_t o, a, u;
+
+       for (o = 0, a = 0, u = 0; u + 1 < len && a < len; o += 2, a++, u += 2) {
+               /* Surrogate pair with code point above U+FFFF */
+               if (utf16[u] >= 0xD8 && utf16[u] <= 0xDB && u + 3 < len &&
+                   utf16[u + 2] >= 0xDC && utf16[u + 2] <= 0xDF) {
+                       out[o++] = utf16[u++];
+                       out[o++] = utf16[u++];
+               }
+               /* Value '_' is replacement for non-representable character */
+               if (ascii[a] == '_') {
+                       out[o] = utf16[u];
+                       out[o + 1] = utf16[u + 1];
+               } else if (utf16[u] == 0x00 && utf16[u + 1] == '_') {
+                       out[o] = 0x00;
+                       out[o + 1] = ascii[a];
+               } else if (utf16[u] == 0x00 && c_toupper(ascii[a]) == c_toupper(utf16[u + 1])) {
+                       out[o] = 0x00;
+                       out[o + 1] = c_isupper(ascii[a]) ? utf16[u + 1] : ascii[a];
+               } else {
+                       return 0;
+               }
+       }
+
+       for (; a < len; o += 2, a++) {
+               out[o] = 0x00;
+               out[o + 1] = ascii[a];
+       }
+
+       return o;
+}
+
 /* iso9660 [+ Microsoft Joliet Extension] */
 static int probe_iso9660(blkid_probe pr, const struct blkid_idmag *mag)
 {
        struct boot_record *boot = NULL;
        struct iso_volume_descriptor *pvd = NULL;
        struct iso_volume_descriptor *joliet = NULL;
+       unsigned char buf[256];
+       size_t len;
        int i;
        uint64_t off;
 
@@ -234,14 +260,17 @@ static int probe_iso9660(blkid_probe pr, const struct blkid_idmag *mag)
        if (joliet)
                blkid_probe_set_version(pr, "Joliet Extension");
 
-       /* Is the Joliet (UTF16BE) label equal to the label in
-        * the PVD? If yes, use PVD label.  The Joliet version
-        * of the label could be trimmed (because UTF16..).
+       /* Label in Joliet is UNICODE (UTF16BE) but can contain only 16 characters. Label in PVD is
+        * subset of ASCII but can contain up to the 32 characters. Non-representable characters are
+        * stored as replacement character '_'. Label in Joliet is in most cases trimmed but UNICODE
+        * version of label in PVD. Based on these facts try to reconstruct original label if label
+        * in Joliet is prefix of the label in PVD (ignoring non-representable characters).
         */
-       if (joliet && !ascii_eq_utf16be(pvd->volume_id, joliet->volume_id, sizeof(pvd->volume_id)))
+       if (joliet && (len = merge_utf16be_ascii(buf, joliet->volume_id, pvd->volume_id, sizeof(pvd->volume_id))) != 0)
+               blkid_probe_set_utf8label(pr, buf, len, UL_ENCODE_UTF16BE);
+       else if (joliet)
                blkid_probe_set_utf8label(pr, joliet->volume_id, sizeof(joliet->volume_id), UL_ENCODE_UTF16BE);
        else
-               /* Joliet not found, let use standard primary label */
                blkid_probe_set_label(pr, pvd->volume_id, sizeof(pvd->volume_id));
 
        return 0;