Index: uspace/lib/label/include/std/fat.h
===================================================================
--- uspace/lib/label/include/std/fat.h	(revision 58fa3e668549d763497f0c6b6a9059794bb2ff4a)
+++ uspace/lib/label/include/std/fat.h	(revision 58fa3e668549d763497f0c6b6a9059794bb2ff4a)
@@ -0,0 +1,127 @@
+/*
+ * Copyright (c) 2008 Jakub Jermar
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ * - The name of the author may not be used to endorse or promote products
+ *   derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/** @addtogroup fs
+ * @{
+ */
+
+#ifndef FAT_FAT_H_
+#define FAT_FAT_H_
+
+#include <stdint.h>
+
+#define BS_BLOCK		0
+#define BS_SIZE			512
+#define DIRENT_SIZE		32
+
+#define FAT12_CLST_MAX    4085
+#define FAT16_CLST_MAX    65525
+
+#define FATAUTO	0
+#define FAT12	12
+#define FAT16	16
+#define FAT32	32
+
+#define FAT_CLUSTER_DOUBLE_SIZE(a) ((a) / 4)
+
+typedef struct fat_bs {
+	uint8_t		ji[3];		/**< Jump instruction. */
+	uint8_t		oem_name[8];
+	/* BIOS Parameter Block */
+	uint16_t	bps;		/**< Bytes per sector. */
+	uint8_t		spc;		/**< Sectors per cluster. */
+	uint16_t	rscnt;		/**< Reserved sector count. */
+	uint8_t		fatcnt;		/**< Number of FATs. */
+	uint16_t	root_ent_max;	/**< Maximum number of root directory
+					     entries. */
+	uint16_t	totsec16;	/**< Total sectors. 16-bit version. */
+	uint8_t		mdesc;		/**< Media descriptor. */
+	uint16_t	sec_per_fat;	/**< Sectors per FAT12/FAT16. */
+	uint16_t	sec_per_track;	/**< Sectors per track. */
+	uint16_t	headcnt;	/**< Number of heads. */
+	uint32_t	hidden_sec;	/**< Hidden sectors. */
+	uint32_t	totsec32;	/**< Total sectors. 32-bit version. */
+
+	union {
+		struct {
+			/* FAT12/FAT16 only: Extended BIOS Parameter Block */
+			/** Physical drive number. */
+			uint8_t		pdn;
+			uint8_t		reserved;
+			/** Extended boot signature. */
+			uint8_t		ebs;
+			/** Serial number. */
+			uint32_t	id;
+			/** Volume label. */
+			uint8_t		label[11];
+			/** FAT type. */
+			uint8_t		type[8];
+			/** Boot code. */
+			uint8_t		boot_code[448];
+			/** Boot sector signature. */
+			uint16_t	signature;
+		} __attribute__ ((packed));
+		struct {
+			/* FAT32 only */
+			/** Sectors per FAT. */
+			uint32_t	sectors_per_fat;
+			/** FAT flags. */
+			uint16_t	flags;
+			/** Version. */
+			uint16_t	version;
+			/** Cluster number of root directory. */
+			uint32_t	root_cluster;
+			/** Sector number of file system information sector. */
+			uint16_t	fsinfo_sec;
+			/** Sector number of boot sector copy. */
+			uint16_t	bscopy_sec;
+			uint8_t		reserved1[12];
+			/** Physical drive number. */
+			uint8_t		pdn;
+			uint8_t		reserved2;
+			/** Extended boot signature. */
+			uint8_t		ebs;
+			/** Serial number. */
+			uint32_t	id;
+			/** Volume label. */
+			uint8_t		label[11];
+			/** FAT type. */
+			uint8_t		type[8];
+			/** Boot code. */
+			uint8_t		boot_code[420];
+			/** Signature. */
+			uint16_t	signature;
+		} fat32 __attribute__ ((packed));
+	};
+} __attribute__ ((packed)) fat_bs_t;
+
+#endif
+
+/**
+ * @}
+ */
Index: uspace/lib/label/src/mbr.c
===================================================================
--- uspace/lib/label/src/mbr.c	(revision 80da8f70107081cb3087b5868745e715a9d6bd46)
+++ uspace/lib/label/src/mbr.c	(revision 58fa3e668549d763497f0c6b6a9059794bb2ff4a)
@@ -39,4 +39,5 @@
 #include <stdlib.h>
 
+#include "std/fat.h"
 #include "std/mbr.h"
 #include "mbr.h"
@@ -89,4 +90,5 @@
 	label_t *label = NULL;
 	mbr_br_block_t *mbr = NULL;
+	fat_bs_t *bs;
 	mbr_pte_t *eptr;
 	uint16_t sgn;
@@ -124,4 +126,6 @@
 	}
 
+	bs = (fat_bs_t *)mbr;
+
 	rc = bd->ops->read(bd->arg, mbr_ba, 1, mbr);
 	if (rc != EOK) {
@@ -145,4 +149,12 @@
 	}
 
+	/*
+	 * We can't really tell whether this is an MBR. Make sure
+	 * this is not actually the BR of a FAT file system
+	 */
+	if (bs->type[0] == 'F' && bs->type[1] == 'A' && bs->type[2] == 'T') {
+		rc = EIO;
+		goto error;
+	}
 
 	label->ext_part = NULL;