After lots of googling for the solution, I only came across unrelated problems, so I thought I'd post my own solution here.
I installed WordPress on Fedora through the package manager. When I tried adding a plugin I got a permission error. Since Google got me nowhere, and after much mucking about with SELinux, I decided to explore WordPress's configuration file manually. The solution was so simple that I couldn't believe all the time I wasted Googling for the answer.
Simply change "true" to "false" in the following lines in wp-config.php:
define('DISALLOW_FILE_MODS', false);
define('AUTOMATIC_UPDATER_DISABLED', false);
That's all! Good luck!