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Bug 1931866 - mkfs.vfat writes corrupted filesystem/partition table when used on whole block device
Summary: mkfs.vfat writes corrupted filesystem/partition table when used on whole bloc...
Keywords:
Status: CLOSED NOTABUG
Alias: None
Product: Fedora
Classification: Fedora
Component: dosfstools
Version: 34
Hardware: x86_64
OS: Linux
unspecified
medium
Target Milestone: ---
Assignee: Jaroslav Škarvada
QA Contact: Fedora Extras Quality Assurance
URL:
Whiteboard:
Depends On: 1931821
Blocks: TRACKER-bugs-affecting-libguestfs
TreeView+ depends on / blocked
 
Reported: 2021-02-23 12:42 UTC by Richard W.M. Jones
Modified: 2021-05-13 19:08 UTC (History)
5 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of: 1931821
Environment:
Last Closed: 2021-05-13 19:08:17 UTC
Type: Bug
Embargoed:

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System ID Private Priority Status Summary Last Updated
Github dosfstools dosfstools issues 161 0 None open mkfs.vfat 4.2 on a whole block device adds bogus partition table 2021-02-23 12:57:49 UTC

Description Richard W.M. Jones 2021-02-23 12:42:47 UTC 
+++ This bug was initially created as a clone of Bug #1931821 +++

Description of problem:

This is a bug in dosfstools which happened between dosfstools-4.1-12.fc33
and dosfstools-4.2-1.fc34.

The following command:

mkfs -t vfat -I -n TEST /dev/sda

previously would create a filesystem directly on /dev/sda.  Now it
creates some kind of corrupted MBR partition table.

If you look at the difference between good (-) and bad (+) you can
see the extra partition table at offset 0x1b0-0x1cf in the image:

--- test1.img.hex       2021-02-23 12:29:49.815043947 +0000
+++ test1-bad.img.hex   2021-02-23 12:30:00.197159306 +0000
@@ -1,6 +1,6 @@
 00000000  eb 3c 90 6d 6b 66 73 2e  66 61 74 00 02 04 04 00  |.<.mkfs.fat.....|
 00000010  02 00 02 00 50 f8 14 00  14 00 01 00 00 00 00 00  |....P...........|
-00000020  00 00 00 00 80 00 29 c1  0d 23 51 54 45 53 54 20  |......)..#QTEST |
+00000020  00 00 00 00 80 00 29 65  e1 e3 4f 54 45 53 54 20  |......)e..OTEST |
 00000030  20 20 20 20 20 20 46 41  54 31 36 20 20 20 0e 1f  |      FAT16   ..|
 00000040  be 5b 7c ac 22 c0 74 0b  56 b4 0e bb 07 00 cd 10  |.[|.".t.V.......|
 00000050  5e eb f0 32 e4 cd 16 cd  19 eb fe 54 68 69 73 20  |^..2.......This |
@@ -12,6 +12,10 @@
 000000b0  72 79 20 61 67 61 69 6e  20 2e 2e 2e 20 0d 0a 00  |ry again ... ...|
 000000c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
 *
+000001b0  00 00 00 00 00 00 00 00  e4 e4 e3 4f 00 00 80 00  |...........O....|
+000001c0  01 00 04 fe ff ff 00 00  00 00 00 50 00 00 00 00  |...........P....|
+000001d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
+*
 000001f0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 55 aa  |..............U.|
 00000200  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
 *
@@ -21,8 +25,8 @@
 00003000  f8 ff ff ff 00 00 00 00  00 00 00 00 00 00 00 00  |................|
 00003010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
 *
-00005800  54 45 53 54 20 20 20 20  20 20 20 08 00 00 a3 63  |TEST       ....c|
-00005810  57 52 57 52 00 00 a3 63  57 52 00 00 00 00 00 00  |WRWR...cWR......|
+00005800  54 45 53 54 20 20 20 20  20 20 20 08 00 00 97 63  |TEST       ....c|
+00005810  57 52 57 52 00 00 97 63  57 52 00 00 00 00 00 00  |WRWR...cWR......|
 00005820  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
 *
 00a00000

This only happens when mkfs is used to create a filesystem on a block
device like /dev/sda, not when you do it on a local file.
Comment 1 Jaroslav Škarvada 2021-05-13 19:08:17 UTC 
Closing, because it's upstream intended behaviour controlled by the --mbr option.
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