libvolume_id: fat - check for signature at end of sector

[elogind.git] / extras / volume_id / lib / fat.c

diff --git a/extras/volume_id/lib/fat.c b/extras/volume_id/lib/fat.c
index 74336b4e6d0df79ca773e382d04d4f4ba5d6e7d3..61a94504381275845d6e399fa945238aadb37ad7 100644 (file)
--- a/extras/volume_id/lib/fat.c
+++ b/extras/volume_id/lib/fat.c
@@ -63,7 +63,7 @@ struct vfat_super_block {
                        uint16_t        flags;
                        uint8_t         version[2];
                        uint32_t        root_cluster;
-                       uint16_t        insfo_sector;
+                       uint16_t        fsinfo_sector;
                        uint16_t        backup_boot;
                        uint16_t        reserved2[6];
                        uint8_t         unknown[3];
@@ -76,6 +76,15 @@ struct vfat_super_block {
        } PACKED type;
 } PACKED;
 
+struct fat32_fsinfo {
+       uint8_t signature1[4];
+       uint32_t reserved1[120];
+       uint8_t signature2[4];
+       uint32_t free_clusters;
+       uint32_t next_cluster;
+       uint32_t reserved2[4];
+} PACKED;
+
 struct vfat_dir_entry {
        uint8_t         name[11];
        uint8_t         attr;
@@ -128,6 +137,7 @@ int volume_id_probe_vfat(struct volume_id *id, uint64_t off)
 {
        struct vfat_super_block *vs;
        struct vfat_dir_entry *dir;
+       struct fat32_fsinfo *fsinfo;
        uint16_t sector_size;
        uint16_t dir_entries;
        uint32_t sect_count;
@@ -141,6 +151,7 @@ int volume_id_probe_vfat(struct volume_id *id, uint64_t off)
        uint64_t root_start;
        uint32_t start_data_sect;
        uint16_t root_dir_entries;
+       uint16_t fsinfo_sect;
        uint8_t *buf;
        uint32_t buf_size;
        uint8_t *label = NULL;
@@ -149,16 +160,19 @@ int volume_id_probe_vfat(struct volume_id *id, uint64_t off)
 
        info("probing at offset 0x%llx", (unsigned long long) off);
 
-       vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
-       if (vs == NULL)
+       buf = volume_id_get_buffer(id, off, 0x400);
+       if (buf == NULL)
+               return -1;
+
+       /* check signature */
+       if (buf[510] != 0x55 || buf[511] != 0xaa)
                return -1;
 
-       /* believe only that's fat, don't trust the version
-        * the cluster_count will tell us
-        */
+       vs = (struct vfat_super_block *) buf;
        if (memcmp(vs->sysid, "NTFS", 4) == 0)
                return -1;
 
+       /* believe only that's fat, don't trust the version */
        if (memcmp(vs->type.fat32.magic, "MSWIN", 5) == 0)
                goto magic;
 
@@ -174,9 +188,7 @@ int volume_id_probe_vfat(struct volume_id *id, uint64_t off)
        if (memcmp(vs->type.fat.magic, "FAT12   ", 8) == 0)
                goto magic;
 
-       /* some old floppies don't have a magic, so we expect the boot code to match */
-
-       /* boot jump address check */
+       /* some old floppies don't have a magic, expect the boot jump address to match */
        if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90) &&
             vs->boot_jump[0] != 0xe9)
                return -1;
@@ -280,6 +292,21 @@ magic:
        goto found;
 
 fat32:
+       /* FAT32 should have a valid signature in the fsinfo block */
+       fsinfo_sect = le16_to_cpu(vs->type.fat32.fsinfo_sector);
+       buf = volume_id_get_buffer(id, off + (fsinfo_sect * sector_size), 0x200);
+       if (buf == NULL)
+               return -1;
+       fsinfo = (struct fat32_fsinfo *) buf;
+       if (memcmp(fsinfo->signature1, "\x52\x52\x61\x41", 4) != 0)
+               return -1;
+       if (memcmp(fsinfo->signature2, "\x72\x72\x41\x61", 4) != 0)
+               return -1 ;
+
+       vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
+       if (vs == NULL)
+               return -1;
+
        strcpy(id->type_version, "FAT32");
 
        /* FAT32 root dir is a cluster chain like any other directory */