libblkid: Add more APFS checking to avoid false positives

1 files changed, 62 insertions, 0 deletions

diff --git a/libblkid/src/superblocks/apfs.c b/libblkid/src/superblocks/apfs.c
index 6303d9b17..67db6eb89 100644
--- a/libblkid/src/superblocks/apfs.c
+++ b/libblkid/src/superblocks/apfs.c
@@ -7,10 +7,72 @@
 
 #include "superblocks.h"
 
+#define APFS_CONTAINER_SUPERBLOCK_TYPE 1
+#define APFS_CONTAINER_SUPERBLOCK_SUBTYPE 0
+#define APFS_STANDARD_BLOCK_SIZE 4096
+
+/*
+ * This struct is much longer than this, but this seems
+ * to contain the useful bits (for now).
+ *
+ * All values are little-endian.
+ */
+struct apfs_super_block {
+	// Generic part to all APFS objects
+	uint64_t checksum;
+	uint64_t oid;
+	uint64_t xid;
+	uint16_t type;
+	uint16_t flags;
+	uint16_t subtype;
+	uint16_t pad;
+
+	// Specific to container header
+	uint32_t magic; // 'NXSB'
+	uint32_t block_size;
+	uint64_t block_count;
+	uint64_t features;
+	uint64_t read_only_features;
+	uint64_t incompatible_features;
+	uint8_t uuid[16];
+};
+
+static int probe_apfs(blkid_probe pr, const struct blkid_idmag *mag)
+{
+	struct apfs_super_block *sb;
+
+	sb = blkid_probe_get_sb(pr, mag, struct apfs_super_block);
+	if (!sb)
+		return errno ? -errno : BLKID_PROBE_NONE;
+
+	if (le16_to_cpu(sb->type) != APFS_CONTAINER_SUPERBLOCK_TYPE)
+		return BLKID_PROBE_NONE;
+
+	if (le16_to_cpu(sb->subtype) != APFS_CONTAINER_SUPERBLOCK_SUBTYPE)
+		return BLKID_PROBE_NONE;
+
+	if (le16_to_cpu(sb->pad) != 0)
+		return BLKID_PROBE_NONE;
+
+	/*
+	 * This check is pretty draconian, but should avoid false
+	 * positives. Can be improved as more APFS documentation
+	 * is published.
+	 */
+	if (le32_to_cpu(sb->block_size) != APFS_STANDARD_BLOCK_SIZE)
+		return BLKID_PROBE_NONE;
+
+	if (blkid_probe_set_uuid(pr, sb->uuid) < 0)
+		return BLKID_PROBE_NONE;
+
+	return BLKID_PROBE_OK;
+}
+
 const struct blkid_idinfo apfs_idinfo =
 {
 	.name		= "apfs",
 	.usage		= BLKID_USAGE_FILESYSTEM,
+	.probefunc	= probe_apfs,
 	.magics		=
 	{
 		{ .magic = "NXSB", .len = 4, .sboff = 32 },