[PATCH 1/2] filetype: Improve FAT detection

[PATCH 1/2] filetype: Improve FAT detection

[Franck Jullien]

We may have some disk with MBR as a first sector. In this case, the
current FAT check returns an error. However, the FAT sector exist and
the MBR can tell us where it is.

This patch make the FAT fs try to find the FAT boot sector on the first
sector of the first partition in case it is not on sector 0.

Signed-off-by: Franck Jullien <franck.jullien@gmail.com>
---
 common/filetype.c  |   55 +++++++++++++++++++++++++++++++++++++++++----------
 include/filetype.h |    1 +
 2 files changed, 45 insertions(+), 11 deletions(-)

diff --git a/common/filetype.c b/common/filetype.c
index e736d43..d07505b 100644
--- a/common/filetype.c
+++ b/common/filetype.c
@@ -26,6 +26,8 @@
 #include <fcntl.h>
 #include <fs.h>
 #include <malloc.h>
+#include <fat.h>
+#include <errno.h>
 
 static const char *filetype_str[] = {
 	[filetype_unknown] = "unknown",
@@ -52,26 +54,45 @@ const char *file_type_to_string(enum filetype f)
 	return NULL;
 }
 
-static int is_fat(u8 *buf)
+int fd;
+
+#define MBR_StartSector		8	/* MBR: Offset of Starting Sector in Partition Table Entry */
+#define BS_55AA			510	/* Boot sector signature (2) */
+#define MBR_Table		446	/* MBR: Partition table offset (2) */
+#define BS_FilSysType32		82	/* File system type (1) */
+#define BS_FilSysType		54	/* File system type (1) */
+
+int is_fat_boot_sector(unsigned char *sector, unsigned long *bootsec)
 {
-	if (get_unaligned_le16(&buf[510]) != 0xAA55)
+	if(bootsec)
+		*bootsec = 0;
+
+	/* Check record signature (always placed at offset 510 even if the sector size is>512) */
+	if (get_unaligned_le16(&sector[BS_55AA]) != 0xAA55)
+		return -ENODEV;
+
+	/* Check "FAT" string */
+	if ((get_unaligned_le32(&sector[BS_FilSysType]) & 0xFFFFFF) == 0x544146)
 		return 0;
 
-	/* FAT */
-	if ((get_unaligned_le32(&buf[54]) & 0xFFFFFF) == 0x544146)
-		return 1;
+	if ((get_unaligned_le32(&sector[BS_FilSysType32]) & 0xFFFFFF) == 0x544146)
+		return 0;
 
-	/* FAT32 */
-	if ((get_unaligned_le32(&buf[82]) & 0xFFFFFF) == 0x544146)
-		return 1;
+	if(bootsec)
+		/* This must be an MBR, so return the starting sector of the
+		 * first partition so we could check if there is a FAT boot
+		 * sector there */
+		*bootsec = get_unaligned_le16(&sector[MBR_Table + MBR_StartSector]);
 
-	return 0;
+	return -ENODEV;
 }
 
 enum filetype file_detect_type(void *_buf)
 {
 	u32 *buf = _buf;
 	u8 *buf8 = _buf;
+	unsigned long bootsec;
+	int ret;
 
 	if (strncmp(buf8, "#!/bin/sh", 9) == 0)
 		return filetype_sh;
@@ -99,7 +120,19 @@ enum filetype file_detect_type(void *_buf)
 		return filetype_aimage;
 	if (strncmp(buf8 + 0x10, "barebox", 7) == 0)
 		return filetype_mips_barebox;
-	if (is_fat(buf8))
+
+	ret = is_fat_boot_sector(buf8, &bootsec);
+	if (ret && bootsec != 0) {
+		/* The first sector is an MBR, now check for FAT in
+		 * the first partition */
+		lseek(fd, (bootsec) * 512, SEEK_SET);
+		ret = read(fd, buf, 512);
+		if (ret < 0)
+			return filetype_unknown;
+		ret = is_fat_boot_sector(buf8, NULL);
+		if (!ret)
+			return filetype_fat;
+	} else
 		return filetype_fat;
 
 	return filetype_unknown;
@@ -107,7 +140,7 @@ enum filetype file_detect_type(void *_buf)
 
 enum filetype file_name_detect_type(const char *filename)
 {
-	int fd, ret;
+	int ret;
 	void *buf;
 	enum filetype type = filetype_unknown;
 
diff --git a/include/filetype.h b/include/filetype.h
index 179ec0f..c60f654 100644
--- a/include/filetype.h
+++ b/include/filetype.h
@@ -24,5 +24,6 @@ enum filetype {
 const char *file_type_to_string(enum filetype f);
 enum filetype file_detect_type(void *_buf);
 enum filetype file_name_detect_type(const char *filename);
+int is_fat_boot_sector(unsigned char *sector, unsigned long *bootsec);
 
 #endif /* __FILE_TYPE_H */
-- 
1.7.1


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[PATCH 2/2] fs/fat: Handle MBR on the first sector

[Franck Jullien]

Use the new filetype.c file detection function to support disk with MBR on the first
sector.

Signed-off-by: Franck Jullien <franck.jullien@gmail.com>
---
 fs/fat/ff.c |   27 ++++++++++++---------------
 1 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/fs/fat/ff.c b/fs/fat/ff.c
index 66db1d6..622845a 100644
--- a/fs/fat/ff.c
+++ b/fs/fat/ff.c
@@ -93,6 +93,7 @@
 #include <errno.h>
 #include <malloc.h>
 #include <linux/ctype.h>
+#include <filetype.h>
 #include "ff.h"			/* FatFs configurations and declarations */
 #include "diskio.h"		/* Declarations of low level disk I/O functions */
 
@@ -1533,7 +1534,8 @@ int follow_path (	/* 0(0): successful, !=0: error code */
  */
 static int check_fs (	/* 0:The FAT BR, 1:Valid BR but not an FAT, 2:Not a BR, 3:Disk error */
 	FATFS *fs,	/* File system object */
-	DWORD sect	/* Sector# (lba) to check if it is an FAT boot record or not */
+	DWORD sect,	/* Sector# (lba) to check if it is an FAT boot record or not */
+	DWORD *bootsec
 )
 {
 	int ret;
@@ -1542,18 +1544,8 @@ static int check_fs (	/* 0:The FAT BR, 1:Valid BR but not an FAT, 2:Not a BR, 3:
 	ret = disk_read(fs, fs->win, sect, 1);
 	if (ret)
 		return ret;
-	/* Check record signature (always placed at offset 510 even if the sector size is>512) */
-	if (LD_WORD(&fs->win[BS_55AA]) != 0xAA55)
-		return -ENODEV;
 
-	/* Check "FAT" string */
-	if ((LD_DWORD(&fs->win[BS_FilSysType]) & 0xFFFFFF) == 0x544146)
-		return 0;
-
-	if ((LD_DWORD(&fs->win[BS_FilSysType32]) & 0xFFFFFF) == 0x544146)
-		return 0;
-
-	return -ENODEV;
+	return is_fat_boot_sector(fs->win, bootsec);
 }
 
 /*
@@ -1565,6 +1557,7 @@ static int chk_mounted (	/* 0(0): successful, !=0: any error occurred */
 )
 {
 	BYTE fmt, b;
+	DWORD first_boot_sect;
 	DWORD bsect, fasize, tsect, sysect, nclst, szbfat;
 	WORD nrsv;
 
@@ -1579,9 +1572,13 @@ static int chk_mounted (	/* 0(0): successful, !=0: any error occurred */
 		return -EIO;
 #endif
 	/* Search FAT partition on the drive. Supports only generic partitionings, FDISK and SFD. */
-	fmt = check_fs(fs, bsect = 0);	/* Check sector 0 if it is a VBR */
-	if (fmt)
-		return fmt; /* No FAT volume is found */
+	fmt = check_fs(fs, bsect = 0, &first_boot_sect);	/* Check sector 0 if it is a VBR */
+	if (fmt && first_boot_sect != 0) {
+		/* Sector 0 is an MBR, now check for FAT in the first partition */
+		fmt = check_fs(fs, bsect = first_boot_sect, NULL);
+		if(fmt)
+			return fmt; /* No FAT volume is found */
+	}
 
 	/* Following code initializes the file system object */
 
-- 
1.7.1


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Re: [PATCH 1/2] filetype: Improve FAT detection

[Jean-Christophe PLAGNIOL-VILLARD]

On 14:32 Sun 16 Sep     , Franck Jullien wrote:
> We may have some disk with MBR as a first sector. In this case, the
> current FAT check returns an error. However, the FAT sector exist and
> the MBR can tell us where it is.
> 
> This patch make the FAT fs try to find the FAT boot sector on the first
> sector of the first partition in case it is not on sector 0.
> 
> Signed-off-by: Franck Jullien <franck.jullien@gmail.com>
> ---
>  common/filetype.c  |   55 +++++++++++++++++++++++++++++++++++++++++----------
>  include/filetype.h |    1 +
>  2 files changed, 45 insertions(+), 11 deletions(-)
> 
> diff --git a/common/filetype.c b/common/filetype.c
> index e736d43..d07505b 100644
> --- a/common/filetype.c
> +++ b/common/filetype.c
> @@ -26,6 +26,8 @@
>  #include <fcntl.h>
>  #include <fs.h>
>  #include <malloc.h>
> +#include <fat.h>
> +#include <errno.h>
>  
>  static const char *filetype_str[] = {
>  	[filetype_unknown] = "unknown",
> @@ -52,26 +54,45 @@ const char *file_type_to_string(enum filetype f)
>  	return NULL;
>  }
>  
> -static int is_fat(u8 *buf)
> +int fd;
> +
> +#define MBR_StartSector		8	/* MBR: Offset of Starting Sector in Partition Table Entry */
> +#define BS_55AA			510	/* Boot sector signature (2) */
> +#define MBR_Table		446	/* MBR: Partition table offset (2) */
> +#define BS_FilSysType32		82	/* File system type (1) */
> +#define BS_FilSysType		54	/* File system type (1) */
> +
> +int is_fat_boot_sector(unsigned char *sector, unsigned long *bootsec)
>  {
> -	if (get_unaligned_le16(&buf[510]) != 0xAA55)
> +	if(bootsec)
> +		*bootsec = 0;
> +
> +	/* Check record signature (always placed at offset 510 even if the sector size is>512) */
> +	if (get_unaligned_le16(&sector[BS_55AA]) != 0xAA55)
> +		return -ENODEV;
> +
> +	/* Check "FAT" string */
> +	if ((get_unaligned_le32(&sector[BS_FilSysType]) & 0xFFFFFF) == 0x544146)
>  		return 0;
>  
> -	/* FAT */
> -	if ((get_unaligned_le32(&buf[54]) & 0xFFFFFF) == 0x544146)
> -		return 1;
> +	if ((get_unaligned_le32(&sector[BS_FilSysType32]) & 0xFFFFFF) == 0x544146)
> +		return 0;
>  
> -	/* FAT32 */
> -	if ((get_unaligned_le32(&buf[82]) & 0xFFFFFF) == 0x544146)
> -		return 1;
> +	if(bootsec)
> +		/* This must be an MBR, so return the starting sector of the
> +		 * first partition so we could check if there is a FAT boot
> +		 * sector there */
> +		*bootsec = get_unaligned_le16(&sector[MBR_Table + MBR_StartSector]);
>  
> -	return 0;
> +	return -ENODEV;
>  }
>  
>  enum filetype file_detect_type(void *_buf)
you work on buf already read you do not knwon where or how

so you can not use fd

this is broken

Best Regards,
J.
>  {

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