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David Tonhofer
Asked: 2024-06-01 20:06:23 +0800 CST

Fedora 40: Apache Httpd refuses to write to "/home" filesystem, but I checked SELinux settings

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I'm installing FosWiki on a Fedora 40 Machine. The FosWiki top directory shall be /home/wikis/foswiki_company. Underneath that there are various directories for content, as well as the log directory.

/home is a separate filesystem (not NFS, just a separate partition on the local machine)

FosWiki is a cheap and cheerful bunch of Perl CGI scripts, so it's just the usual CGI setup.

It turns out that I cannot even get into the setup page of FosWiki because the setup script is unable to create the log file (i.e. Perl's open() call fails). The apparent problem is that "the filesystem is read-only".

SELinux is enabled and I'm checking the AVC denial messages. There seems to be none.

Below is the relevant structure of the filesystem.

  • The orange elements are where the logfile is meant to go, but doing so proves to be impossible. I also tried with the tmp subdirectory, same problem.
  • The brown element are an experiment whereby I modified the CGI script so that the log file would be written to a (suitably permission-ed) directory /home/tmp, which fails.
  • The green elements are an experiment whereby I modified the CGI script so that the log file would be written to a (suitably permission-ed) directory /var/www/tmp. This works.

Additionally, the SELinux boolean for allowing httpd access to home directories, usually off, has been switched on, no difference, it seems to be irrelevant to this problem:

# semanage boolean -l -C
SELinux boolean                State  Default Description

httpd_can_network_connect      (on   ,   on)  Allow httpd to can network connect
httpd_enable_homedirs          (on   ,   on)  Allow httpd to enable homedirs
selinuxuser_execmod            (on   ,   on)  Allow selinuxuser to execmod

Additionally, if I su - apache (after configuring a shell for user apachein /etc/passwd), I can create or write to any of the log files.

So it's a process-related thing, not a user-related thing.

Additionally, I tried disabling SELinux, but got the same problem.

So it's unlikely to be SELinux.

What am I missing? What could stop Apache httpd from writing to the /home filesystem?

The current filesystem

apache-2.4

1 Answers

  1. Best Answer

    The problem is due to systemd, which has recently branched out into controlling process access to /home. This may be useful, but doesn't contribute to clarity on a system that already has POSIX access control and SELinux access control.

    Having a sudden brainwave and searching for "have systemd block access to /home" was key.

    The option is ProtectHome (added in version 214 and indeed, I am at version 255). The manual says:

    ProtectHome=

    Takes a boolean argument or the special values "read-only" or "tmpfs". If true, the directories /home/, /root, and /run/user are made inaccessible and empty for processes invoked by this unit. If set to "read-only", the three directories are made read-only instead. If set to "tmpfs", temporary file systems are mounted on the three directories in read-only mode. The value "tmpfs" is useful to hide home directories not relevant to the processes invoked by the unit, while still allowing necessary directories to be made visible when listed in BindPaths= or BindReadOnlyPaths=.

    etc.

    By default this option is read-only. We need to change it to no.

    # systemctl show httpd | grep Home
ProtectHome=read-only

    So, let's do it. Run

    systemctl edit httpd

    and set up the override file to contain:

    [Service]
ProtectHome=no

    After saving that file and restarting Apache httpd:

    systemctl restart httpd

    The process can create and write the files in their respective directories under /home.

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