[PATCH v4 4/6] ntfs: validate resident volume name values on lookup

[DaeMyung Kang <charsyam@gmail.com>]

The shared lookup-time attribute validator now has a safe caller path for
$VOLUME_NAME corruption: ntfs_write_volume_label() no longer treats
lookup errors as an absent label, and the mount path reinitializes its
search context before continuing to $VOLUME_INFORMATION.

Add $VOLUME_NAME-specific resident value validation. A volume name is
stored as a UTF-16LE string, so reject odd byte lengths, and reject
values longer than the NTFS volume label limit. Empty labels remain
valid.

Also reject non-resident $VOLUME_NAME records. $VOLUME_NAME is required
to be resident, like $FILE_NAME; a crafted non-resident record would
otherwise pass lookup and ntfs_write_volume_label() would remove it as if
it were a normal resident attribute.

Signed-off-by: DaeMyung Kang <charsyam@gmail.com>
---
 fs/ntfs/attrib.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/fs/ntfs/attrib.c b/fs/ntfs/attrib.c
index 98e0b8ea2edd..7e293b85ad19 100644
--- a/fs/ntfs/attrib.c
+++ b/fs/ntfs/attrib.c
@@ -607,6 +607,14 @@ static bool ntfs_file_name_attr_value_is_valid(const u8 *value, const u32 value_
 			value_length - offsetof(struct file_name_attr, file_name);
 }
 
+static bool ntfs_volume_name_attr_value_is_valid(const u32 value_length)
+{
+	if (value_length & 1)
+		return false;
+
+	return value_length <= NTFS_MAX_LABEL_LEN * sizeof(__le16);
+}
+
 struct ntfs_resident_attr_value {
 	const u8 *data;
 	u32 len;
@@ -657,7 +665,7 @@ static bool ntfs_attr_value_is_valid(struct ntfs_volume *vol,
 	u32 min_len;
 
 	if (a->non_resident) {
-		if (a->type == AT_FILE_NAME)
+		if (a->type == AT_FILE_NAME || a->type == AT_VOLUME_NAME)
 			goto corrupt;
 		if (!ntfs_non_resident_attr_value_is_valid(a))
 			goto corrupt;
@@ -676,6 +684,10 @@ static bool ntfs_attr_value_is_valid(struct ntfs_volume *vol,
 		if (!ntfs_file_name_attr_value_is_valid(value.data, value.len))
 			goto corrupt;
 		break;
+	case AT_VOLUME_NAME:
+		if (!ntfs_volume_name_attr_value_is_valid(value.len))
+			goto corrupt;
+		break;
 	}
 	return true;
 
-- 
2.43.0