From: "Heinz Nimmervoll" <bt1now@gmx.at>
Subject: superblock completely overwritten
Date: Tue, 13 Dec 2016 16:39:07 +0100
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I still got no answer for my problem thats why I try it here... hopefully you could help me out.
 
System:

Embedded board with Atmel SAM9x25
Debian Wheezy Kernel 3.11.6
32GB Samsung SDHC card with ext4 root- partition (journal activated)
 

After system running two weeks or so superblock from rootfs (ext4) at block 0 got overwritten with "trash data".
This is happening with like 20% of the embedded devices.
 
hex comparision between faulty and good superblock starting at byte 1024:
 
Before (good):
 
00000000  00 ee 02 00 00 b8 0b 00  00 96 00 00 ab a9 05 00  |................|
00000010  c3 0c 02 00 00 00 00 00  02 00 00 00 02 00 00 00  |................|
00000020  00 80 00 00 00 80 00 00  40 1f 00 00 9e 68 46 58  |........@....hFX|
00000030  9e 68 46 58 2e 00 64 00  53 ef 01 00 01 00 00 00  |.hFX..d.S.......|
00000040  0f 35 ff 55 00 00 00 00  00 00 00 00 01 00 00 00  |.5.U............|
00000050  00 00 00 00 0b 00 00 00  00 01 00 00 3c 00 00 00  |............<...|
00000060  46 02 00 00 7b 00 00 00  3b 9e 9c 82 4d 90 4d ed  |F...{...;...M.M.|
00000070  84 41 3a 05 5c 37 fb a8  72 6f 6f 74 66 73 00 00  |.A:.\7..rootfs..|
00000080  00 00 00 00 00 00 00 00  2f 6d 65 64 69 61 2f 76  |......../media/v|
00000090  69 72 74 75 61 6c 73 69  67 69 2f 72 6f 6f 74 66  |irtualsigi/rootf|
000000a0  73 00 73 00 00 00 00 00  00 00 00 00 00 00 00 00  |s.s.............|
000000b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000000c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 bb 00  |................|
000000d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000000e0  08 00 00 00 00 00 00 00  00 00 00 00 41 41 7f 29  |............AA.)|
000000f0  b2 43 48 94 ab 07 f8 fa  38 1c 2e 33 01 01 00 00  |.CH.....8..3....|
00000100  0c 00 00 00 00 00 00 00  b8 40 6a 52 0a f3 01 00  |.........@jR....|
00000110  04 00 00 00 00 00 00 00  00 00 00 00 00 40 00 00  |.............@..|
00000120  00 00 05 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000130  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000140  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 04  |................|
00000150  00 00 00 00 00 00 00 00  00 00 00 00 1c 00 1c 00  |................|
00000160  02 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000170  00 00 00 00 04 00 00 00  cd 8a 94 00 00 00 00 00  |................|
00000180  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
 
After (corrupted):
 
00000000  00 00 00 00 a4 81 00 00  dd 00 00 00 24 8e 5d 54  |............$.]T|
00000010  7e 8e 5d 54 18 a6 9f 41  00 00 00 00 00 00 01 00  |~.]T...A........|
00000020  08 00 00 00 00 00 08 00  01 00 00 00 0a f3 01 00  |................|
00000030  04 00 00 00 00 00 00 00  00 00 00 00 01 00 00 00  |................|
00000040  54 b2 01 00 00 00 00 00  00 00 00 00 00 00 00 00  |T...............|
00000050  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000060  00 00 00 00 00 00 00 00  86 2a 63 08 00 00 00 00  |.........*c.....|
00000070  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000080  00 00 00 00 1c 00 00 00  60 c9 e6 31 00 00 00 00  |........`..1....|
00000090  00 00 00 00 7c 8e 5d 54  9c b0 2a ec 00 00 00 00  |....|.]T..*.....|
000000a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00000100  00 00 00 00 a4 81 00 00  0f 00 00 00 67 4d 6b 52  |............gMkR|
00000110  67 4d 6b 52 63 87 84 4f  00 00 00 00 00 00 01 00  |gMkRc..O........|
00000120  08 00 00 00 00 00 08 00  01 00 00 00 0a f3 01 00  |................|
00000130  04 00 00 00 00 00 00 00  00 00 00 00 01 00 00 00  |................|
00000140  74 07 03 00 00 00 00 00  00 00 00 00 00 00 00 00  |t...............|
00000150  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000160  00 00 00 00 00 00 00 00  19 1e 79 cd 00 00 00 00  |..........y.....|
00000170  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000180  00 00 00 00 1c 00 00 00  e4 14 dc e7 00 00 00 00  |................|
00000190  98 6a 83 72 67 4d 6b 52  98 6a 83 72 00 00 00 00  |.j.rgMkR.j.r....|
000001a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00000200  00 00 00 00 a4 81 00 00  88 0c 00 00 44 8c 5d 54  |............D.]T|
00000210  4d 8c 5d 54 9c 8e 52 54  00 00 00 00 00 00 01 00  |M.]T..RT........|
00000220  08 00 00 00 00 00 08 00  01 00 00 00 0a f3 01 00  |................|
00000230  04 00 00 00 00 00 00 00  00 00 00 00 01 00 00 00  |................|
00000240  7b e0 01 00 00 00 00 00  00 00 00 00 00 00 00 00  |{...............|
00000250  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000260  00 00 00 00 00 00 00 00  4e 09 63 08 00 00 00 00  |........N.c.....|
00000270  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000280  00 00 00 00 1c 00 00 00  f8 b4 6f 14 00 00 00 00  |..........o.....|
00000290  00 00 00 00 48 8c 5d 54  28 cc 55 82 00 00 00 00  |....H.]T(.U.....|
000002a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00000300  00 00 00 00 a4 81 00 00  94 05 00 00 68 4d 6b 52  |............hMkR|
00000310  69 4d 6b 52 54 0f df 4f  00 00 00 00 00 00 01 00  |iMkRT..O........|
00000320  08 00 00 00 00 00 08 00  01 00 00 00 0a f3 01 00  |................|
00000330  04 00 00 00 00 00 00 00  00 00 00 00 01 00 00 00  |................|
00000340  8c 07 03 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000350  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000360  00 00 00 00 00 00 00 00  27 1e 79 cd 00 00 00 00  |........'.y.....|
00000370  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000380  00 00 00 00 1c 00 00 00  b0 07 a2 3a 00 00 00 00  |...........:....|
00000390  04 a9 de 29 68 4d 6b 52  04 a9 de 29 00 00 00 00  |...)hMkR...)....|
000003a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|

- How is it possible, that even the magic number (and everything else) got overwritten?
- Why could it ever be overwritten?
 
Thank you so much!