partitions/efi: Fix partition name parsing in GUID partition entry

GUID partition entry defined to have a partition name as 36 UTF-16LE
code units. This means that on big-endian platforms ASCII symbols
would be read with 0xXX00 efi_char16_t character code. In order to
correctly extract ASCII characters from a partition name field we
should be converted from 16LE to CPU architecture.

The problem exists on all big endian platforms.

[ mingo: Minor edits. ]

Fixes: eec7ecfede ("genhd, efi: add efi partition metadata to hd_structs")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nikolai Merinov <n.merinov@inango-systems.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200308080859.21568-29-ardb@kernel.org
Link: https://lore.kernel.org/r/797777312.1324734.1582544319435.JavaMail.zimbra@inango-systems.com/

block/partitions/efi.c

@@ -656,6 +656,31 @@ static int find_valid_gpt(struct parsed_partitions *state, gpt_header **gpt,
         return 0;
 }
 
+/**
+ * utf16_le_to_7bit(): Naively converts a UTF-16LE string to 7-bit ASCII characters
+ * @in: input UTF-16LE string
+ * @size: size of the input string
+ * @out: output string ptr, should be capable to store @size+1 characters
+ *
+ * Description: Converts @size UTF16-LE symbols from @in string to 7-bit
+ * ASCII characters and stores them to @out. Adds trailing zero to @out array.
+ */
+static void utf16_le_to_7bit(const __le16 *in, unsigned int size, u8 *out)
+{
+	unsigned int i = 0;
+
+	out[size] = 0;
+
+	while (i < size) {
+		u8 c = le16_to_cpu(in[i]) & 0xff;
+
+		if (c && !isprint(c))
+			c = '!';
+		out[i] = c;
+		i++;
+	}
+}
+
 /**
  * efi_partition(struct parsed_partitions *state)
  * @state: disk parsed partitions
@@ -692,7 +717,6 @@ int efi_partition(struct parsed_partitions *state)
 
 	for (i = 0; i < le32_to_cpu(gpt->num_partition_entries) && i < state->limit-1; i++) {
 		struct partition_meta_info *info;
-		unsigned label_count = 0;
 		unsigned label_max;
 		u64 start = le64_to_cpu(ptes[i].starting_lba);
 		u64 size = le64_to_cpu(ptes[i].ending_lba) -
@@ -713,14 +737,7 @@ int efi_partition(struct parsed_partitions *state)
 		/* Naively convert UTF16-LE to 7 bits. */
 		label_max = min(ARRAY_SIZE(info->volname) - 1,
 				ARRAY_SIZE(ptes[i].partition_name));
-		info->volname[label_max] = 0;
-		while (label_count < label_max) {
-			u8 c = ptes[i].partition_name[label_count] & 0xff;
-			if (c && !isprint(c))
-				c = '!';
-			info->volname[label_count] = c;
-			label_count++;
-		}
+		utf16_le_to_7bit(ptes[i].partition_name, label_max, info->volname);
 		state->parts[i + 1].has_info = true;
 	}
 	kfree(ptes);

block/partitions/efi.h

@@ -88,7 +88,7 @@ typedef struct _gpt_entry {
 	__le64 starting_lba;
 	__le64 ending_lba;
 	gpt_entry_attributes attributes;
-	efi_char16_t partition_name[72 / sizeof (efi_char16_t)];
+	__le16 partition_name[72/sizeof(__le16)];
 } __packed gpt_entry;
 
 typedef struct _gpt_mbr_record {