Re: [PATCH v2 rev log added] fstests: btrfs verify hardening agaist duplicate fsid

[Nikolay Borisov <nborisov@suse.com>]

On 8.10.18 г. 21:28 ч., Anand Jain wrote:
> We have a known bug in btrfs, that we let the device path be changed
> after the device has been mounted. So using this loop hole the new
> copied device would appears as if its mounted immediately after its
> been copied. So this test case reproduces this issue.
> 
> For example:
> 
> Initially.. /dev/mmcblk0p4 is mounted as /
> 
> lsblk
> NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
> mmcblk0     179:0    0 29.2G  0 disk
> |-mmcblk0p4 179:4    0    4G  0 part /
> |-mmcblk0p2 179:2    0  500M  0 part /boot
> |-mmcblk0p3 179:3    0  256M  0 part [SWAP]
> `-mmcblk0p1 179:1    0  256M  0 part /boot/efi
> 
> btrfs fi show
> Label: none  uuid: 07892354-ddaa-4443-90ea-f76a06accaba
>     Total devices 1 FS bytes used 1.40GiB
>     devid    1 size 4.00GiB used 3.00GiB path /dev/mmcblk0p4
> 
> Copy mmcblk0 to sda
> dd if=/dev/mmcblk0 of=/dev/sda
> 
> And immediately after the copy completes the change in the device
> superblock is notified which the automount scans using
> btrfs device scan and the new device sda becomes the mounted root
> device.
> 
> lsblk
> NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
> sda           8:0    1 14.9G  0 disk
> |-sda4        8:4    1    4G  0 part /
> |-sda2        8:2    1  500M  0 part
> |-sda3        8:3    1  256M  0 part
> `-sda1        8:1    1  256M  0 part
> mmcblk0     179:0    0 29.2G  0 disk
> |-mmcblk0p4 179:4    0    4G  0 part
> |-mmcblk0p2 179:2    0  500M  0 part /boot
> |-mmcblk0p3 179:3    0  256M  0 part [SWAP]
> `-mmcblk0p1 179:1    0  256M  0 part /boot/efi
> btrfs fi show /
> Label: none  uuid: 07892354-ddaa-4443-90ea-f76a06accaba
>     Total devices 1 FS bytes used 1.40GiB
>     devid    1 size 4.00GiB used 3.00GiB path /dev/sda4
> 
> The bug is quite nasty that you can't either unmount /dev/sda4 or
> /dev/mmcblk0p4. And the problem does not get solved until you take
> the sda out of the system on to another system to change its fsid using
> the 'btrfstune -u' command.

Is there a pending fix for this?

> 
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
> v1->v2: 
>   dont play around with dev patch use it as it is.
>   do not use SCRATCH_MNT instead create it at the TEST_DIR and its related
>    changes.
>   golden out changes
>    
>  tests/btrfs/173     | 88 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  tests/btrfs/173.out |  6 ++++
>  tests/btrfs/group   |  1 +
>  3 files changed, 95 insertions(+)
>  create mode 100755 tests/btrfs/173
>  create mode 100644 tests/btrfs/173.out
> 
> diff --git a/tests/btrfs/173 b/tests/btrfs/173
> new file mode 100755
> index 000000000000..b466ae921e19
> --- /dev/null
> +++ b/tests/btrfs/173
> @@ -0,0 +1,88 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2018 Oracle. All Rights Reserved.
> +#
> +# FS QA Test 173
> +#
> +# Fuzzy test for FS image duplication.
> +#  Could be fixed by
> +#    [patch] btrfs: harden agaist duplicate fsid
> +#
> +seq=`basename $0`
> +seqres=$RESULT_DIR/$seq
> +echo "QA output created by $seq"
> +
> +here=`pwd`
> +tmp=/tmp/$$
> +status=1	# failure is the default!
> +trap "_cleanup; exit \$status" 0 1 2 3 15
> +
> +mnt=$TEST_DIR/$seq.mnt
> +_cleanup()
> +{
> +	rm -rf $mnt > /dev/null 2>&1
> +	cd /
> +	rm -f $tmp.*
> +}
> +
> +# get standard environment, filters and checks
> +. ./common/rc
> +. ./common/filter
> +
> +# remove previous $seqres.full before test
> +rm -f $seqres.full
> +
> +# real QA test starts here
> +
> +# Modify as appropriate.
> +_supported_fs btrfs
> +_supported_os Linux
> +_require_scratch_dev_pool 2
> +_scratch_dev_pool_get 2
> +
> +dev_foo=$(echo $SCRATCH_DEV_POOL | awk '{print $1}')
> +dev_bar=$(echo $SCRATCH_DEV_POOL | awk '{print $2}')

Naming devices _foo and _bar just shows you could not care less about
the test. Either use sane names - primary_dev/secondary dev or device_1
and device_2.

> +
> +echo dev_foo=$dev_foo >> $seqres.full
> +echo dev_bar=$dev_bar >> $seqres.full
> +echo | tee -a $seqres.full
> +
> +rm -rf $mnt > /dev/null 2>&1

So what is $mnt? I can see it's used by very few tests and it's not
obvious? Generally you should either define it as a local variable or
use one of the SCRATCH_MNT/TEST_MNT global variables. Also I checked
with Eric re. the use of $mnt in tests and his conclusion is :

"<sandeen> looks like a bug"

> +mkdir $mnt
> +_mkfs_dev $dev_foo
> +_mount $dev_foo $mnt
> +
> +check_btrfs_mount()
> +{
> +	local x=$(findmnt $mnt | grep -v TARGET | awk '{print $2}')
> +	[[ $x == $dev_foo ]] && echo DEV_FOO
> +	[[ $x == $dev_bar ]] && echo DEV_BAR
> +}

Same thing here re. DEV_(FOO|BAR).

> +
> +echo MNT $(check_btrfs_mount)
> +
> +for sb_bytenr in 65536 67108864
> +do
> +	echo -n "dd status=none if=$dev_foo of=$dev_bar bs=1 "\
> +		"seek=$sb_bytenr skip=$sb_bytenr count=4096" >> $seqres.full
> +	dd status=none if=$dev_foo of=$dev_bar bs=1 seek=$sb_bytenr \
> +				skip=$sb_bytenr count=4096 >> $seqres.full 2>&1
> +	echo ..:$? >> $seqres.full

This is an overkill, just use dd ... >/dev/null 2>&1, no one cares about
the output of that. Also use DIO so that sb's are directly written to
the devices.

> +done
> +
> +#Original device is mounted, scan of its clone should fail
> +$BTRFS_UTIL_PROG device scan $dev_bar >> $seqres.full 2>&1
> +echo btrfs device scan dev_bar ...:$?| tee -a $seqres.full
> +
> +echo MNT $(check_btrfs_mount)
> +
> +#Original device scan should be successful
> +$BTRFS_UTIL_PROG device scan $dev_foo >> $seqres.full 2>&1
> +echo btrfs device scan dev_foo ...:$?| tee -a $seqres.full
> +
> +umount $mnt > /dev/null 2>&1
> +_scratch_dev_pool_put
> +
> +# success, all done
> +status=0
> +exit
> diff --git a/tests/btrfs/173.out b/tests/btrfs/173.out
> new file mode 100644
> index 000000000000..3c7e3fb4e3f7
> --- /dev/null
> +++ b/tests/btrfs/173.out
> @@ -0,0 +1,6 @@
> +QA output created by 173
> +
> +MNT DEV_FOO
> +btrfs device scan dev_bar ...:1
> +MNT DEV_FOO
> +btrfs device scan dev_foo ...:0

It seems the output is really pointless it should just be "Silence is
golden". Then in the test you would do all your run-time checks of
what's the source of the mount etc etc and if your expectations don't
match you fail the test and don't output "Silence is golden" which would
signal success. Check for example

> diff --git a/tests/btrfs/group b/tests/btrfs/group
> index 45782565c3b7..b2f1393f3e97 100644
> --- a/tests/btrfs/group
> +++ b/tests/btrfs/group
> @@ -175,3 +175,4 @@
>  170 auto quick snapshot
>  171 auto quick qgroup
>  172 auto quick punch
> +173 volume
>