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Bug 1588451 - Don't use relative socket paths for NBD
Summary: Don't use relative socket paths for NBD
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: libguestfs
Version: 7.5
Hardware: Unspecified
OS: Unspecified
unspecified
unspecified
Target Milestone: rc
: ---
Assignee: Richard W.M. Jones
QA Contact: Virtualization Bugs
URL:
Whiteboard:
Depends On: 1588447
Blocks:
TreeView+ depends on / blocked
 
Reported: 2018-06-07 11:35 UTC by Peter Krempa
Modified: 2019-01-16 07:55 UTC (History)
5 users (show)

Fixed In Version: libguestfs-1.38.2-5.el7
Doc Type: If docs needed, set a value
Doc Text:
Clone Of: 1588447
Environment:
Last Closed: 2018-10-30 07:45:35 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHEA-2018:3021 0 None None None 2018-10-30 07:46:21 UTC

Description Peter Krempa 2018-06-07 11:35:33 UTC 
Libvirt's schema never allowed them, but the code did not enforce it.

+++ This bug was initially created as a clone of Bug #1588447 +++

Description of problem:

https://www.redhat.com/archives/libvir-list/2018-June/msg00490.html

If you have a reference to a relative path for a socket,
these no longer work.  They used to in older versions of libvirt,
and they still work on certain architectures (for example, x86_64
still works, but i686 fails).

libvirt should either reject them if they are wrong, or be fixed
so that it works like it used to.

If you decide to reject them, please clone this bug for
libguestfs because we will need to fix the paths that we
pass to libvirt.

Version-Release number of selected component (if applicable):

libvirt 4.4.0-1.fc29

How reproducible:

Unknown, only on certain architectures at certain times.
I was only able to reliably reproduce on i686 in a Koji
build using qemu:///session.

Steps to Reproduce:

1. Start nbdkit serving over a local Unix domain socket in the
current directory:

rm -f my.sock
nbdkit -f -v -U my.sock example1

2. Create a guest which has a disk like:

  <disk device="disk" type="network">
    <source protocol="nbd">
      <host transport="unix" socket="my.sock"/>
    </source>
    <target dev="sda" bus="scsi"/>
    <driver name="qemu" type="raw" cache="writeback"/>
  </disk>

3. Start the guest under qemu:///session

4. Fails with:

  internal error: process exited while connecting to monitor: 2018-06-06T17:02:5
4.450507Z qemu-system-i386: -drive
file=nbd+unix://?socket=my.sock,format=raw,if=none,id=drive-scsi0-0-0-0,cache=w
riteback: Failed to connect socket my.sock: No such file or directory [code=1
int1=-1]

--- Additional comment from Peter Krempa on 2018-06-07 13:29:12 CEST ---

The XML schema for the network disk unix socket backing always called for an 'absFilePath' so the given XML is not valid.

I think we want to enforce absolute path even in the code for APPS which don't pass correct XML to libvirt.
Comment 2 Richard W.M. Jones 2018-06-07 11:39:51 UTC 
Yes we'll have to "absolutize" (is that a word?) these paths before
adding them to the XML, easy fix.
Comment 4 Richard W.M. Jones 2018-06-14 08:07:02 UTC 
I don't have a very good reproducer because it only happens
sometimes on some architectures.  We could only reproduce it
under Koji, on i686, with the very latest libvirt.

This _may_ reproduce the problem:

  rm -f test.sock
  nbdkit -U test.sock example1
  guestfish --format=raw -a 'nbd://?socket=test.sock' run
  killall nbdkit

Note the error message when the bug has been reproduced is:

  Failed to connect socket test.sock: No such file or directory

If you see other errors (eg. Permission denied) then you are not
reproducing the error.  Permission denied can happen because of
SELinux.  In fact to get guestfish to connect you'll probably
need to set SELinux to Permissive.

You can also try the full path which should NOT reproduce the
problem, eg:

  guestfish --format=raw -a 'nbd://?socket=/var/tmp/test.sock' run

The change we are going to make to libguestfs is to turn
relative paths (test.sock) into absolute paths (/var/tmp/test.sock).
Comment 5 Richard W.M. Jones 2018-06-14 10:25:57 UTC 
https://www.redhat.com/archives/libguestfs/2018-June/thread.html#00053
Comment 6 Richard W.M. Jones 2018-06-15 13:51:16 UTC 
v2 of patch which fixes the tests:

https://www.redhat.com/archives/libguestfs/2018-June/msg00067.html
Comment 7 YongkuiGuo 2018-06-20 08:47:42 UTC 
Reproduced with the following packages:
libvirt-4.4.0-1.fc29.i686
libguestfs-1.38.2-1.fc28.i686
nbdkit-1.2.2-1.fc28.i686

Steps:
1. Update libvirt on fedora28 host and then install nbdkit related packages.
2. rm -f test.sock
3. nbdkit -U test.sock example1
4. guestfish --format=raw -a 'nbd://?socket=test.sock' run
---------------------------------------------------------
Original error from libvirt: internal error: process exited while connecting to monitor: 2018-06-20T08:40:16.518284Z qemu-system-i386: -drive file=nbd+unix://?socket=test.sock,format=raw,if=none,id=drive-scsi0-0-0-0,cache=writeback: Failed to connect socket test.sock: No such file or directory [code=1 int1=-1]
---------------------------------------------------------


I can reproduce this bug, but when I turn the relative paths to absolute paths, another error pops up.

# killall nbdkit
# rm -rf test.sock 
# nbdkit -U test.sock example1
# guestfish --format=raw -a 'nbd://?socket=/home/test.sock' run
----------------------------------------------------------
Original error from libvirt: internal error: process exited while connecting to monitor: 2018-06-20 08:43:20.115+0000: Domain id=5 is tainted: high-privileges
2018-06-20 08:43:20.115+0000: Domain id=5 is tainted: custom-argv
2018-06-20T08:43:20.197767Z qemu-system-i386: -drive file=nbd:unix:/home/test.sock,format=raw,if=none,id=drive-scsi0-0-0-0,cache=writeback: request for write access conflicts with read-only export [code=1 int1=-1]

rjones, do you know the reason about the error above?
Comment 8 Richard W.M. Jones 2018-06-20 09:07:05 UTC 
> rjones, do you know the reason about the error above?

Ooops, my example was wrong.

Try changing the nbdkit command to use the example3 plugin
which is writable:

  nbdkit -U test.sock example3

BTW you shouldn't need to run the tests as root.
Comment 9 YongkuiGuo 2018-06-20 10:30:40 UTC 
> Try changing the nbdkit command to use the example3 plugin
> which is writable:
> 
>   nbdkit -U test.sock example3
> 
> BTW you shouldn't need to run the tests as root.
The example3 plugin is OK. Thanks a lot.
Comment 10 Richard W.M. Jones 2018-06-21 10:02:12 UTC 
v3:
https://www.redhat.com/archives/libguestfs/2018-June/msg00092.html
Comment 11 Richard W.M. Jones 2018-06-21 12:20:58 UTC 
Upstream in
https://github.com/libguestfs/libguestfs/commit/70bc83f893e6e0daf20ca7c9b7bfe875ceaed594
which will be included in libguestfs >= 1.39.6.
I'll also backport this to 1.38 at some point.

Note the current bug is against RHEL 7 so I'm not going to close it.
Comment 13 YongkuiGuo 2018-08-09 06:49:48 UTC 
Verified with packages:
libguestfs-1.38.2-8.el7.x86_64
nbdkit-1.2.6-1.el7.x86_64
libvirt-4.5.0-3.el7.x86_64

Steps:

1.Install nbdkit and nbdkit-example-plugins packages on rhel7.6 host, then run the following commands: 
$ rm -f test.sock
$ nbdkit -U test.sock example3
$ guestfish --format=raw -a 'nbd://?socket=test.sock' run

No error pops up. Verified it.
Comment 15 errata-xmlrpc 2018-10-30 07:45:35 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHEA-2018:3021
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