Troubleshooting: Volume attachment fails due to SELinux denials in Fedora downstream distributions
| June 7, 2023
All Longhorn versions.
Commonly seen in Fedora downstream distributions (e.g. Fedora, RHEL, Rocky, CentOS, etc.) when container-selinux is
updated beyond version 2.189.0. This can happen unexpectedly and can catch administrators off guard.
Symptoms are the same as those discussed in a previous KB article that focused on OKD.
All volumes are stuck in an attach/detach loop. dmesg and ausearch on storage nodes reveal SELinux issues:
-> dmesg
...
[Sat Dec 10 18:52:01 2022] audit: type=1400 audit(1670698321.515:7214): avc: denied { dac_override } for pid=231579 comm="iscsiadm" capability=1 scontext=system_u:system_r:iscsid_t:s0 tcontext=system_u:system_r:iscsid_t:s0 tclass=capability permissive=0
[Sat Dec 10 18:52:01 2022] audit: type=1300 audit(1670698321.515:7214): arch=c000003e syscall=83 success=no exit=-13 a0=55b9035185c0 a1=1f8 a2=ffffffffffffff00 a3=0 items=0 ppid=231163 pid=231579 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm="iscsiadm" exe="/usr/sbin/iscsiadm" subj=system_u:system_r:iscsid_t:s0 key=(null)
[Sat Dec 10 18:52:01 2022] audit: type=1327 audit(1670698321.515:7214): proctitle=697363736961646D002D6D00646973636F76657279002D740073656E6474617267657473002D700031302E3133312E312E31363
-> ausearch -m AVC -ts recent
...
----
time->Wed Jun 7 19:33:17 2023
type=PROCTITLE msg=audit(1686166397.967:2849): proctitle=697363736961646D002D6D00646973636F76657279002D740073656E6474617267657473002D700031302E38382E302E39
type=PATH msg=audit(1686166397.967:2849): item=1 name="/var/lib/iscsi/nodes/iqn.2019-10.io.longhorn:vol-name/10.88.0.9,3260,1" nametype=CREATE cap_fp=0 cap_fi=0 cap_fe=0 cap_fver=0 cap_frootid=0
type=PATH msg=audit(1686166397.967:2849): item=0 name="/var/lib/iscsi/nodes/iqn.2019-10.io.longhorn:vol-name/" inode=54532024 dev=fc:01 mode=040600 ouid=0 ogid=0 rdev=00:00 obj=unconfined_u:object_r:iscsi_var_lib_t:s0 nametype=PARENT cap_fp=0 cap_fi=0 cap_fe=0 cap_fver=0 cap_frootid=0
type=CWD msg=audit(1686166397.967:2849): cwd="/"
type=SYSCALL msg=audit(1686166397.967:2849): arch=c000003e syscall=83 success=no exit=-13 a0=562f10bf5540 a1=1f8 a2=fffffffffffffef0 a3=0 items=2 ppid=53345 pid=53577 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=1 comm="iscsiadm" exe="/usr/sbin/iscsiadm" subj=unconfined_u:system_r:iscsid_t:s0 key=(null)
type=AVC msg=audit(1686166397.967:2849): avc: denied { dac_override } for pid=53577 comm="iscsiadm" capability=1 scontext=unconfined_u:system_r:iscsid_t:s0 tcontext=unconfined_u:system_r:iscsid_t:s0 tclass=capability permissive=0
The root cause is the same as was discussed in a previous KB article that focused on
OKD. A permissions issue in
open-iscsi causes iscsiadm to create directories under /var/lib/iscsi without the execute bit. When it later
needs to access these directories, it cannot do so without the dac_override capability. Updated versions of
container-selinux do not grant iscsiadm this capability when run from a container.
This issue was fixed in open-iscsi
v2.1.4, but a
patch used to build the iscsi-initiator-utils RPM overrode the change in a couple of lines, leaving Fedora
downstream distributions affected. Now that many of these distributions are running with an updated container-selinux
package, a workaround is required.
It is generally not recommended (and difficult) to install an out-of-band version of open-iscsi not provided by your
distribution maintainers. Instead, the dac_override permission must be provided to iscsid_t. This can be done by
running the following command (or similar) on all nodes before using Longhorn.
echo '(allow iscsid_t self (capability (dac_override)))' > local_longhorn.cil && semodule -vi local_longhorn.cil
While it is not ideal to have to grant the dac_override capability, it is important to recognize that affected
versions of iscsi-initiator-utils cannot run without it, even outside of Longhorn. Usually, iscsiadm is executed
by an unconfined root user, and uses this capability implicitly.
Multiple Kubernetes distributions already apply this fix by default:
If you are running an affected OS with an up-to-date container-selinux and your Kubernetes distribution doesn’t
already apply the fix for you, we provide a DaemonSet that can make the necessary change on all nodes.
git clone https://github.com/longhorn/longhorn.git
cd longhorn
kubectl apply -f deploy/prerequisite/longhorn-iscsi-selinux-workaround.yaml
A PR was submitted to the Fedora project. If it is accepted, additional capabilities will no longer be required as downstream distributions adopt the changes.
open-iscsi fix:
https://github.com/open-iscsi/open-iscsi/pull/244/commits/6df400925cfa9e723375c6f61524473703054220Recent articles
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