Re: btrfs check segfaults after flipping 2 Bytes

[Niklas Fischer <niklas@niklasfi.de>]

What I forgot to mention:

`uname -r`: 3.17.0-0.rc6.git2.1.fc22.x86_64
`btrfs --version`: Btrfs v3.16

regards,
Niklas

Am 01.10.2014 um 22:29 schrieb Niklas Fischer:
> Hello,
> 
> I was trying to determine how btrfs reacts to disk errors, when I
> discovered, that flipping two Bytes, supposedly inside of a file can
> render the filesystem unusable. Here is what I did:
> 
> 1. dd if=/dev/zero of=/dev/sdg2 bs=1M
> 2. mkfs.btrfs /dev/sdg2
> 3. mount /dev/sdg2 /tmp/btrfs
> 4. echo "hello world this is some text" > /tmp/btrfs/hello
> 5. umount /dev/sdg2
> 
> this should result in this image [1]
> 
> in the following steps /dev/sdg2 is altered. Basically, we want to apply
> s/world/wirld/g
> 
> 6. dd if=/dev/sdg2 of=/tmp/sdg2 bs=1M
> 7. edit /tmp/sdg2 in ghex, find & replace all occurences of "world" with
> "wirld" (two occurences found), save as /tmp/sdg2_new
> 8. dd if=/tmp/sdg2_new of=/dev/sdg2 bs=1M
> 
> /dev/sdg2 now looks like this [2]
> 
> now, when I try mounting /dev/sdg2:
> 
> """22:21 root@localhost ~#
> LANG=EN mount /dev/sdg2 /tmp/btrfs/
> mount: mount /dev/sdg2 on /tmp/btrfs failed: Cannot allocate memory"""
> 
> ok, so let us try btrfs check
> 
> """22:21 root@localhost ~#
> LANG=EN btrfs check /dev/sdg2
> checksum verify failed on 4222976 found F22E71BD wanted CE334502
> checksum verify failed on 4222976 found F22E71BD wanted CE334502
> Csum didn't match
> Checking filesystem on /dev/sdg2
> UUID: ea2843f1-e8aa-420f-acf8-6ef13f6c6753
> checking extents
> Speicherzugriffsfehler (Speicherabzug geschrieben)"""
> 
> that last line reads "Segfault, memory dumped". Is this behaviour expected?
> 
> Kind regards,
> Niklas
> 
> [1] tgz: https://gigamove.rz.rwth-aachen.de/d/id/R5CKikxbYTBdqs
>     raw: https://gigamove.rz.rwth-aachen.de/d/id/VgMXAicS7CGEjt
> [2] tgz: https://gigamove.rz.rwth-aachen.de/d/id/cEebNYne9ppFy4
>     raw: https://gigamove.rz.rwth-aachen.de/d/id/ATJa7wpfEWdfL2
>