Check required exec functions for disablement

PHP 8+ makes disabled functions act as if not defined at all. To account
for this and the increased likelihood of hosts to disable functions
associated with process execution, check for function existence before
running mandatory calls to exec, shell_exec, or escapeshellarg. Other
calls like those in the default ExternalImageMagick derivative creator
can be avoided through configuration.

(#1001)

application/libraries/Omeka/File/MimeType/Detect/Strategy/FileCommand.php

@@ -14,7 +14,11 @@ class Omeka_File_MimeType_Detect_Strategy_FileCommand implements Omeka_File_Mime
     public function detect($file)
     {
         $disabled = explode(', ', ini_get('disable_functions'));
-        if (in_array('shell_exec', $disabled)) {
+        if (!function_exists('escapeshellarg')
+            || !function_exists('shell_exec')
+            || in_array('escapeshellarg', $disabled)
+            || in_array('shell_exec', $disabled)
+        ) {
             // shell_exec is disabled.
             return false;
         }

application/models/File.php

@@ -308,7 +308,9 @@ public function setDefaults($filepath, array $options = array())
     {
         $this->size = filesize($filepath);
         $this->authentication = md5_file($filepath);
-        $this->type_os = substr(trim(exec('file -b ' . trim(escapeshellarg($filepath)))), 0, 255);
+        if (function_exists('exec') && function_exists('escapeshellarg')) {
+            $this->type_os = substr(trim(exec('file -b ' . trim(escapeshellarg($filepath)))), 0, 255);
+        }
         $this->filename = basename($filepath);
         $this->metadata = '';
     }