Chapter 8. Bug fixes

Installer now lists all PPC PreP Boot or BIOS Boot partitions during custom partitioning

Previously, when adding multiple PPC PreP Boot or BIOS Boot partitions during custom partitioning, the Custom Partitioning screen displayed only one partition of a related type. As a consequence, the Custom Partitioning screen did not reflect the real state of the intended partitioning layout, making the partitioning process difficult and non-transparent.

The installer now adds configuration options correctly into the yum repo files

Previously, the installer did not add configuration options correctly into yum repo files while including and excluding packages from additional installation repositories. With this update, yum repo files are created correctly. As a result, using the --excludepkgs= or --includepkgs= options in the repo kickstart command now excludes or includes the specified packages during installation as expected.

Using the filename DHCP option no longer blocks downloading the kickstart file for installation

Previously, when building a path for getting the kickstart file from an NFS server, the installer did not consider the filename DHCP option. As a consequence, the installer did not download the kickstart file and was blocking the installation process. With this update, the filename DHCP option correctly constructs a path to the kickstart file. As a result, the kickstart file is downloaded properly, and the installation process starts correctly.

The installer now creates a new GPT disk layout while custom partitioning

Previously, the installer did not change the disk layout to GPT when inst.gpt was specified on the kernel command line, and the user removed all partitions from a disk with the MBR disk layout on the custom partitioning spoke. As a consequence, the MBR disk layout remained on the disk.

The --size parameter of the composer-cli compose start command now treats its values as MiB

Previously, when using the composer-cli compose start --size size_value blueprint_name image_type command, the composer-cli tool treated the --size parameter values as byte units. This update fixes the issue, and the --size parameter values are now correctly used in the MiB format.

RPM no longer hangs during a transaction involving the fapolicyd service restart

Previously, if you tried to update a package that caused the fapolicyd service to be restarted, for example, systemd, the RPM transaction stopped responding because the fapolicyd plug-in failed to communicate with the fapolicyd daemon.

Security YUM upgrade is now possible for packages that change their architecture through the upgrade

Patch for BZ#2088149 introduced with RHBA-2022:7711 caused a regression where YUM upgrade using security filters skipped packages that changed their architecture from or to noarch through the upgrade. Consequently, the missing security upgrades for these packages could leave the system in a vulnerable state.

Reverting a YUM upgrade transaction is now possible for a package group or environment

Previously, the yum history rollback command failed when attempting to revert an upgrade transaction for a package group or an environment.

wsmancli handles HTTP 401 Unauthorized statuses correctly

The wsmancli utility for managing systems using Web Services Management protocol now handles authentication to better conform to RFC 2616.

The translator.sty LaTeX style document has been added

Previously, the translator.sty LaTeX style document, which is necessary for certain tools that depend on texlive-beamer, was missing. As a consequence, these tools failed with a LaTeX Error: File `translator.sty' not found. error. This update adds the missing texlive-translator package that contains the translator.sty LaTeX style document. As a result, tools that depend on texlive-beamer work correctly.

ReaR handles excluded DASDs on the IBM Z architecture correctly

Previously on the IBM Z architecture, ReaR reformatted all connected Direct Access Storage Devices (DASD) during the recovery process, including those DASDs that users excluded from the saved layout and did not intend to restore their content. As a consequence, if you excluded some DASDs from the saved layout, their data were lost during system recovery. With this update, ReaR no longer formats excluded DASDs during system recovery, including the device from which the ReaR rescue system was booted (using the zIPL bootloader). You are also prompted to confirm the DASD formatting script before ReaR reformats DASDs. This ensures that the data on excluded DASDs survive a system recovery.

ReaR no longer fails to restore non-LVM XFS filesystems

Previously, when you used ReaR to restore a non-LVM XFS filesystems with certain settings and disk mapping, ReaR created the file system with the default settings instead of the specified settings.

rsync no longer fails while using regular expressions for extended attributes

Previously, the rsync utility for transferring and synchronizing files was not able to handle extended attributes in RHEL 8 correctly. For example, if you passed the --delete option together with the --filter '-x string.*' option for extended attributes to the rsync command, and a file on your system satisfied the regular expression, this resulted in an error message stating protocol incompatibilities. With this update, the rsync utility handles extended attributes correctly and you can use regular expressions for these attributes.

Scans and remediations correctly ignore SCAP Audit rules Audit key

Previously, Audit watch rules that were defined without an Audit key (-k or -F key) encountered the following problems:

crypto-policies no longer creates unnecessary symlink

During system installation, the crypto-policies scriptlet creates symlinks from the /usr/share/crypto-policies/DEFAULT file or /usr/share/crypto-policies/FIPS in FIPS mode and saves them in the /etc/crypto-policies/back-ends directory. Previously, crypto-policies incorrectly included directories, and created a /etc/crypto-policies/back-ends/.config symlink that pointed to the /usr/share/crypto-policies/DEFAULT or /usr/share/crypto-policies/FIPS directories. With this update, crypto-policies does not create symlinks from directories, and therefore does not create this unnecessary symlink.

crypto-policies now disable NSEC3DSA for BIND

Previously, the system-wide cryptographic policies did not control the NSEC3DSA algorithm in the BIND configuration. Consequently, NSEC3DSA, which does not meet current security requirements, was not disabled on DNS servers. With this update, all cryptographic policies disable NSEC3DSA in the BIND configuration by default.

Libreswan no longer rejects SHA-1 signature verification in the FUTURE and FIPS cryptographic policies

Previously, from update to 4.9, Libreswan rejected SHA-1 signature verification in the FUTURE and FIPS cryptographic policies, and peer authentication failed when authby=rsasig or authby=rsa-sha1 connection options were used. This update reverts this behavior by relaxing how Libreswan handles the crypto-policies settings. As a consequence, you can now use the authby=rsasig and authby=rsa-sha1 connection options using SHA-1 signature verification.

crontab bash scripts no longer execute in incorrect context

Previously, a bug fix published in erratum RHBA-2022:7691 used too general transition rule. Consequently, a bash script executed from the crontab file was executed in the rpm_script_t context instead of the system_cronjob_t context. With this update, bash scripts are now executed in the correct context.

selinux-policy supports service execution in SAP Host Agent

Previously, the SELinux policy did not support the insights-client service interacting with SAP Host Agent and other services. As a consequence, some commands did not work correctly when started from Red Hat Insights. With this update, the SELinux policy supports SAP service execution. As a result, SAP services started from Insights run successfully.

selinux-policy now allows pmcd to execute its private memfd: objects

Previously, the SELinux policy did not allow the pmcd process from the Performance Co-Pilot (PCP) framework to execute its private memory file-system objects (memfd:). Consequently, SELinux denied the Performance Metric Domain Agent (PMDA) BPF Compiler Collection (BCC) service to execute memfd: objects. In this update, the SELinux policy contains new rules for pcmd. As a result, pmcd can now execute memfd: objects with SELinux in enforcing mode.

SELinux policy allows sysadm_r to use subscription-manager

Previously, users in the sysadm_r SELinux role were not allowed to execute some subcommands of the subscription-manager utility. Consequently, the subcommands failed to read the memory device. This update adds a new rule to the SELinux policy that allows the sysadm_t type to read /dev/mem. As a consequence, the subscription-manager subcommands do not fail.

samba-dcerpcd process now works correctly with nscd

Previously, the samba-dcerpcd process could not communicate with the nscd process because of the SELinux policy. Consequently, the samba-dcerpcd service did not work properly when the nscd service was enabled. With this update, the SELinux policy has been updated with new rules for samba-dcerpcd.

vlock now works properly for confined users

Previously, the confined user could not use vlock due to SELinux policy. Consequently, the vlock command did not work properly for confined users. With this update, the SELinux policy has been updated with new rules for confined users.

Confined users now can log in without a reported denial

Previously, SELinux policy did not allow all permissions needed to log in a SELinux confined user using GUI. Consequently, AVC denials were audited and some services like dbus or pulseaudio did not work properly. With this update, the SELinux policy has been updated with new rules for confined users.

insights-client now has additional permissions in the SELinux policy

The updated insights-client service requires additional permissions, which were not included in the previous versions of the selinux-policy packages. As a consequence, certain components of insights-client did not work correctly with SELinux in enforcing mode, and the system reported access vector cache (AVC) error messages. This update adds the missing permissions to the SELinux policy. As a result, insights-client now works correctly without reporting AVC errors.

The SELinux policy allows smb access to user shares

Previously, the samba-dcerpcd process was separated from the smb service, but did not have access to user shares. As a consequence, smb clients could not access files on user smb shares. This update adds rules to the SELinux policy for managing user home content for the samba-dcerpcd binary when the samba_enable_home_dirs boolean is enabled. As a result, samba-dcerpcd can access user shares when samba_enable_home_dirs is on.

The SELinux policy now allows confined administrators to access ipmi devices when IPMItool runs

Previously, the SELinux policy did not allow confined administrators to read and write ipmi devices when the IPMItool utility is run. As a consequence, when a confined administrator ran ipmitool, it failed. This update adds allow rules to selinux-policy for administrators assigned to the sysadm_r SELinux role. As a result, if a confined administrator runs ipmitool it works correctly.

SCAP Security Guide rule file_permissions_sshd_private_key is aligned with STIG configuration RHEL-08-010490

Previously, the implementation of rule file_permissions_sshd_private_key allowed private SSH keys to be readable by the ssh_keys group with mode 0644, while DISA STIG version RHEL-08-010490 required private SSH keys to have mode 0600. As a consequence, evaluation with DISA’s automated STIG benchmark failed for configuration RHEL-08-010490.

The sudo_require_reauthentication SCAP Security Guide rule accepts correct spacing in sudoers

Previously, a bug in the checking of the xccdf_org.ssgproject.content_rule_sudo_require_reauthentication rule caused it to require specific spacing between the timestamp_timeout key and its value in the /etc/sudoers file and the /etc/sudoers.d directory. Consequently, valid and compliant syntax caused the rule to fail incorrectly. With this update, the check for xccdf_org.ssgproject.content_rule_sudo_require_reauthentication has been updated to accept blank spaces around the equal sign. As a result, the rule accepts correct and compliant definitions of timestamp_timeout with any of the following spacing formats:

Old Kerberos rules changed to notapplicable in new versions of RHEL

Previously, some Kerberos-related rules failed while scanning against the DISA STIG profile on RHEL 8.8 and later systems in FIPS mode, even though the system should have been compliant. This was caused by the following rules:

scap-security-guide STIG profiles no longer require specific text in /etc/audit/rules.d/11-loginuid.rules

Previously, the SCAP rule audit_immutable_login_uids used in RHEL 8 profiles stig and stig_gui passed only if file /etc/audit/rules.d/11-loginuid.rules contained exact text. This is, however, not necessary to fulfill the STIG requirement (RHEL-08-030122). With this update, the new rule audit_rules_immutable_login_uids replaces audit_immutable_login_uids in RHEL 8 stig and stig_gui profiles. As a result, you can now specify the --loginuid-immutable parameter that fulfills the rule in any file with the .rules extension within the /etc/audit/rules.d directory or in the /etc/audit/audit.rules file, depending on usage of auditctl or augen-rules.

Rules for CIS profiles in scap-security-guide are better aligned

Previously, some rules were incorrectly assigned to certain Center for Internet Security (CIS) profiles (cis, cis_server_l1, cis_workstation_1, and cis_workstation_l2). As a consequence, scanning according to some CIS profiles could skip rules from the CIS benchmark or check for unnecessary rules.

Clevis ignores commented devices in crypttab

Previously, Clevis tried to unlock commented devices in the crypttab file, causing the clevis-luks-askpass service to run even if the device was not valid. This caused unnecessary service runs and made it difficult to troubleshoot.

Clevis no longer requests too much entropy from pwmake

Previously, the pwmake password generation utility displayed unwanted warnings when Clevis used pwmake to create passwords for storing data in LUKS metadata, which caused Clevis to use lower entropy. With this update, Clevis is limited to 256 entropy bits provided to pwmake, which eliminates an unwanted warning and uses the correct amount of entropy.

logrotate no longer incorrectly signals Rsyslog in log rotation

Previously, the argument order was incorrectly set in the logrotate script, which caused a syntax error. This resulted in logrotate not correctly signaling Rsyslog during log rotation.

Rsyslog no longer crashes due to a bug in imklog

Previously, Rsyslog could encounter a segmentation fault if the imklog module was enabled and a free() call using an invalid object was freed during use. With this update, the freed object is correctly deallocated at the correct place. As a result, the segmentation fault no longer occurs.

USBGuard no longer causes a confusing warning

Previously, a race condition could happen in USBGuard when a parent process finished sooner than the first child process. As a consequence, systemd reported that a process was present with a wrongly identified parent PID (PPID). With this update, a parent process waits for the first child process to finish in working mode. As a result, systemd no longer reports such warnings.

The usbguard service file did not define OOMScore

Previously, the usbguard service file did not define the OOMScoreAdjust option. Consequently, the process could be identified as a candidate for killing before unprivileged processes when the system resources are closed to running out. With this update, the new OOMScoreAdjust setting was introduced to the usbguard.service file, to disable OOM killing processes of the usbguard unit.

USBGuard saves rules even if RuleFile is not defined

Previously, if the RuleFile configuration directive in USBGuard was set but RuleFolder was not, the rule set could not be changed. With this update, you can now change the rule set even if RuleFolder is set but RuleFile is not. As a result, you can modify the permanent policy in USBGuard to permanently save newly added rules.

xdp-tools rebased to version 1.2.10

The xdp-tools packages have been upgraded to upstream version 1.2.10, which provides a number of bug fixes over the previous version.

conntrackd functions properly even if HashSize and HashLimit are not set manually

Previously, the conntrackd service did not set default values for the HashSize and HashLimit configuration variables. Consequently, conntrackd could become unstable or stop functioning entirely if you did not specify those values. The problem has been fixed by making the configuration reader set the default values for HashSize and HashLimit before conntrackd parses the configuration file. As a result, conntrackd now functions correctly even if you do not specify the values.

The nm-cloud-setup service no longer removes routes and manually-configured secondary IP addresses from interfaces

Based on the information received from the cloud environment, the nm-cloud-setup service configures network interfaces. Previously, administrators had to disable nm-cloud-setup to manually configure routes and secondary IP addresses on interfaces to avoid that the service removes them. This update adds a flag to the Reapply() function to preserve externally added addresses and routes. As a result, administrators no longer need to disable the nm-cloud-setup service in the mentioned scenario.

kpatch-patch works correctly on systems with an idle isolated CPU

Previously, when you attempted to install kpatch-patch CVE mitigation packages on systems with the kernel CPU isolation feature, the kpatch-patch RPMs did install, but failed to load their CVE mitigation kernel module. With this fix, the two features co-exist, and you can now successfully deploy kpatch CVE fixes when CPU isolation is in place.

Enabling VMD works again

Previously, the operating system would fail to boot if Volume Management Device (VMD) was enabled. This update provides numerous bug fixes essential for VMD to work as expected.

System works correctly without the soft lockup while starting a VDO volume

Due to fixing a Kernel Application Binary Interface (kABI) bug in the pv_mmu_ops structure, RHEL 8.7 systems with kernel version 4.18.0-425.10.1.el8_7, that is RHEL-8.7.0.2-BaseOS, hung or encountered a kernel panic due to soft lockup while starting a Virtual Data Optimizer (VDO) volume.

VDO driver bug no longer causing device freezes through journal blocks

Previously, a bug in the VDO driver caused the system to mark some journal blocks as waiting for metadata updates. This problem was triggered when increasing the size of the VDO pool or the logical volume on top of it, or when using the pvmove and lvchange operations on LVM tools managed VDO devices. The bug was caused by incomplete resets that left some journal pages unavailable for use, and an incorrect notion of how many slots in the recovery journal were available to be filled. As a result, the device would freeze.

pcs no longer allows you to modify cluster properties that should not be changed

Previously, the pcs command line interface allowed you to modify cluster properties that should not be changed or for which change does not take effect. With this fix, pcs no longer allows you to modify these cluster properties: cluster-infrastructure, cluster-name, dc-version, have-watchdog, and last-lrm-refresh.

pcs now displays cluster properties that are not explicitly configured

Previously, a pcs command to display the value of a specific cluster property did not list values that are not explicitly configured in the CIB. With this fix, if a cluster property is not set pcs displays the default value for the property.

Cluster resources that call crm_mon now stop cleanly at shutdown

Previously, the crm_mon utility returned a nonzero exit status while Pacemaker was in the process of shutting down. Resource agents that called crm_mon in their monitor action, such as ocf:heartbeat:pqsql, could incorrectly return a failure at cluster shutdown. With this fix, crm_mon returns success even if the cluster is in the process of shutting down. Resources that call crm_mon now stop cleanly at cluster shutdown.

OCF resource agent metadata actions can now call crm_node without causing unexpected fencing

As of RHEL 8.5, OCF resource agent metadata actions blocked the controller and crm_node queries performed controller requests. As a result, if an agent’s metadata action called crm_node, it blocked the controller for 30 seconds until the action timed out. This could cause other actions to fail and the node to be fenced.

Enabling a single resource and monitoring operation no longer enables monitoring operations for all resources in a resource group

Previously, after unmanaging all resources and monitoring operations in a resource group, managing one of the resources in that group along with its monitoring operation re-enabled the monitoring operations for all resources in the resource group. This could trigger unexpected cluster behavior.

Pacemaker now rechecks resource assignments immediately when resource order changes

As of RHEL 8.7, Pacemaker did not recheck resource assignments when the order of resources in the CIB changed with no changes to the resource definition. If configuration reordering would cause resources to move, that would not take place until the next natural transition, up to the value of cluster-recheck-interval-property. This could cause issues if resource stickiness is not configured for a resource.

You can install SciPy using pip on all architectures

Previously, the openblas-devel package did not contain a pkg-config file for the OpenBLAS library. As a consequence, in certain scenarios, it was impossible to determine the compiler and linker flags using the pkgconf utility while compiling with OpenBLAS. For example, this caused a failure of the pip install scipy command on the 64-bit IBM Z and IBM Power Systems, Little Endian architectures.

Functions in go no longer cause memory leak

Previously, the EVP_PKEY_sign_raw and EVP_PKEY_verify_raw functions did not call free to clean the memory. Consequently, the memory leaked and has not been recovered. With this updated, the EVP_PKEY_sign_raw and EVP_PKEY_verify_raw functions now call free and memory is not leaking.

golang now supports 4096 bit keys in x509 FIPS mode

Previously, golang did not support the 4096 bit keys in x509 FIPS mode. Consequently, when the user used 4096 bit keys the program crashed. With this update, golang now supports 4096 bit keys in x509 FIPS mode.

libffi can now probe for executable memory with SELinux enabled

By default, libffi does not probe for executable memory when SELinux is enabled. As a consequence, programs which use libffi closures and fork() without immediately executing some other processes terminate unexpectedly when SELinux is enabled. With this update, libffi looks for a /etc/sysconfig/libffi-force-shared-memory-check-first file and, if it exists, probes for executable memory regardless of if SELinux is enabled. As a result, programs using libffi can safely fork() without crashing with SELinux enabled.

Implemented big endian support in OpenSSL bindings for golang

Previously, the OpenSSL bindings for golang did not have support for big-endian, leading to potential issues with the conversion of BigInt values. As a result, the crypto routines were unable to perform this conversion. To fix this issue, big-endian support was implemented in the OpenSSL bindings for golang. As a result, conversions from BigInt are now successful, and the tests pass as expected.

Authentication to external IdPs that require a client secret is now possible

Previously, SSSD did not properly pass client secrets to external identity providers (IdPs). Consequently, authentication failed against external IdPs that you previously configured with the ipa idp-add --secret command to require a client secret. With this update, SSSD passes the client secret to the IdP and users can authenticate.

IdM now supports setting hostmasks for sudo rules using Ansible

Previously, the ipa sudorule-add-host command allowed setting a hostmask to be used by the sudo rule, but this option was not present in the ansible-freeipa package. With this update, you can now use the ansible-freeipa hostmask variable to define a list of hostmasks to which a particular sudo rule, defined in Identity Management (IdM), applies.

The scheduled time of the changelog compaction now works correctly

Previously, when you configured a custom scheduled time for the changelog compaction, the server did not apply the new setting, and the changelog compaction could start during peak times. With this release, the server now correctly applies the custom time of the changelog compaction.

IdM clients correctly retrieve information for trusted AD users when their names contain mixed case characters

Previously, if you attempted a user lookup or authentication of a user, and that trusted Active Directory (AD) user contained mixed case characters in their names and they were configured with overrides in IdM, an error was returned preventing users from accessing IdM resources.

mod_auth_gssapi now respects GssapiLocalName setting for user mapping

Before the update mod_auth_gssapi-1.6.1-9.el8, a regression allowed mod_auth_gssapi to convert a principal to a local username using the auth_to_local_names setting from the krb5 configuration without explicitly enabling this behavior. As a result, an httpd setup using mod_auth_gssapi could unintentionally map client identities based on the auth_to_local_names setting, even if the GssapiLocalName option was not set to On. With this update, the original behavior is restored. GssapiLocalName must now be explicitly set to On in the httpd configuration to enable user mapping via auth_to_local_names.

Matrox G200e now works correctly with a VGA display

Previously, your display might have shown no graphical output if you used the following system configuration:

The web console NBDE binding steps now work also on volume groups with a root file system

In RHEL 8.8.0, due to a bug in the code for determining whether or not the user was adding a Tang key to the root file system, the binding process in the web console crashed when there was no file system on the LUKS container at all. Because the web console displayed the error message TypeError: Qe(…​) is undefined after you had clicked the Trust key button in the Verify key dialog, you had to perform all the required steps in the command-line interface in the described scenario.

The nbde_client system role now correctly handles different names of clevis-luks-askpass

The nbde_client system role has been updated to handle the systems on which the clevis-luks-askpass systemd unit has a different name. The role now correctly works with different names of clevis-luks-askpass on managed nodes, which requires unlocking also LUKS-encrypted volumes that mount late in the boot process.

The ha_cluster system role logs no longer display unencrypted passwords and secrets

The ha_cluster system role accepts parameters that can be passwords or other secrets. Previously, some of the tasks would log their inputs and outputs. As a result, the role logs could contain unencrypted passwords and other secrets.

Clusters configured with ha_cluster system role to use SBD and not start on boot now work correctly

Previously, if a user configured a cluster using the ha_cluster system role to use SBD and not start on boot, then the SBD service was disabled and SBD did not start. With this fix, the SBD service is always enabled if a cluster is set to use SBD whether or not the cluster is configured to start on boot.

Setting stonith-watchdog-timeout property with the ha_cluster system role now works in a stopped cluster

Previously, when you set the stonith-watchdog-timeout property with the ha_cluster system role in a stopped cluster, the property reverted to its previous value and the role failed. With this fix, configuring the stonith-watchdog-timeout property by using the ha_cluster system role works properly.

Enabling implicit files provider to fix rhel-system-roles SSSD configuration

A disabled SSSD implicit files provider caused the rhel-system-roles modules to create an invalid System Security Services Daemon (SSSD) configuration. This update unconditionally enables the files provider and as a result, the SSSD configuration created by rhel-system-roles now works as expected.

Network traffic is now directed through the intended network interface when using initscripts with the networking RHEL system role

Previously, when using the initscripts provider, the routing configuration for network connections did not specify the output device that the traffic should go through. Consequently, the kernel could use a different output device than the user intended. Now, if the network interface name is specified in the playbook for the connection, it is used as the output device in the route configuration file. This aligns the behavior with NetworkManager, which configures the output device in routes when activating profiles on devices. As a result, the users can ensure that the traffic is directed through the intended network interface.

The nbde_client_clevis role no longer reports traceback to users

Previously, the nbde_client_clevis role sometimes failed in exception, causing a traceback and reporting sensitive data, such as the encryption_password field, back to the user. With this update, the role no longer reports sensitive data, only the appropriate error messages.

System time on nested VMs now works reliably

Previously, system time on nested virtual machines (VMs) in some cases desynchronised from the Level 0 and level 1 hosts. This also sometimes caused the nested VM to become unresponsive or terminate unexpectedly.

Network traffic performance in virtual machines is no longer reduced

Previously, RHEL virtual machines had, in some cases, decreased performance when handling high levels of network traffic. The underlying code has been fixed and the network traffic performance is not affected anymore.

Virtual machines using memfd run as expected

Previously, virtual machines (VMs) running on the 64-bit IBM Z processor architecture that used memfd to back memory with hugepages failed to run. With this update, the problem has been fixed and VMs using memfd can now be defined on the 64-bit IBM Z processor architecture. As a result, you can now run VMs which use memfd to back the memory with hugepages.

System time in VMs now synchronizes correctly with the host

Previously, the KVM module performed the real-time clock (RTC) synchronization less frequently than intended. As a consequence, the system time in VMs hosted on RHEL 8 sometimes did not correctly reflect the system time on the host. This update fixes the RTC scheduling in KVM, which prevents the described problem from occurring.