libblkid: Add more APFS checking to avoid false positives

diff --git a/libblkid/src/superblocks/apfs.c b/libblkid/src/superblocks/apfs.c
index 6303d9b172f0ef8a38bf92efa163a26094e4f363..67db6eb895067b17fbf6594a50b71132b79d70df 100644 (file)
--- 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 },