Set the eeprom cache permissions to 755

Issue and Root Cause:
The issue arises because, after a system reboot, the permissions of /var/cache/sonic/decode-syseeprom/ or its file
/var/cache/sonic/decode-syseeprom/syseeprom_cache may be incorrectly set. This misconfiguration can cause the
Platform API to require root privileges for access.

This problem has been observed in various platforms, such as the AS7326_56X, where running show platform syseeprom
results in errors due to permission issues.

Solution:
To address this, it's essential to ensure that the cache directory and its files have the correct permissions set upon
system startup. Implementing a fix that adjusts these permissions appropriately can prevent the Platform API from
requiring root privileges, thereby resolving the issue.

Author: PJHsieh

sonic_platform_base/sonic_eeprom/eeprom_base.py

@@ -295,9 +295,21 @@ def write_cache(self, e):
         if self.cache_name:
             F = None
             try:
+                # Ensure the directory exists
+                directory = os.path.dirname(self.cache_name)
+
+                if not os.path.exists(directory):
+                    os.makedirs(directory)
+
+                # Set directory permissions to 755
+                os.chmod(directory, 0o755)
+
                 F = open(self.cache_name, "wb")
                 F.seek(self.s)
                 F.write(e)
+
+                # Set file permissions to 755
+                os.chmod(self.cache_name, 0o755)
             except IOError as e:
                 raise IOError("Failed to write cache : %s" % (str(e)))
             finally:

tests/eeprom_base_test.py

@@ -2,7 +2,7 @@
 import pytest
 import subprocess
 from unittest import mock
-from unittest.mock import patch, MagicMock
+from unittest.mock import patch, MagicMock, mock_open
 from sonic_platform_base.sonic_eeprom import eeprom_base, eeprom_tlvinfo
 EEPROM_SYMLINK = "vpd_info"
 EEPROM_HEX_FILE = "syseeprom.hex"
@@ -200,6 +200,40 @@ def test_set_eeprom_invalid_field(self, mock_print):
         mock_print.assert_called_with("Error: invalid field '0x20'")
         assert e.value.code == 1
 
+    @mock.patch("builtins.open", new_callable=mock.mock_open)
+    @mock.patch("os.makedirs")
+    @mock.patch("os.path.exists", return_value=False)
+    @mock.patch("os.chmod")
+    def test_write_cache(self, mock_chmod, mock_exists, mock_makedirs, mock_open):
+        # Create an instance of TlvInfoDecoder with a mock cache_name
+        eeprom_decoder = eeprom_tlvinfo.TlvInfoDecoder("/dev/null", 0, "", True)
+        eeprom_decoder.cache_name = "/tmp/mock_cache"
+
+        # Mock EEPROM data to write
+        mock_eeprom_data = b"mock_eeprom_data"
+
+        # Call the write_cache method
+        eeprom_decoder.write_cache(mock_eeprom_data)
+
+        # Verify that os.makedirs was called with the correct directory
+        mock_makedirs.assert_called_once_with("/tmp")
+
+        # Verify that os.chmod was called to set directory permissions
+        mock_chmod.assert_any_call("/tmp", 0o755)
+
+        # Verify that the file was opened in write-binary mode
+        mock_open.assert_called_once_with("/tmp/mock_cache", "wb")
+
+        # Verify that the file's seek method was called with the correct offset
+        mock_open().seek.assert_called_once_with(eeprom_decoder.s)
+
+        # Verify that the file's write method was called with the EEPROM data
+        mock_open().write.assert_called_once_with(mock_eeprom_data)
+
+        # Verify that os.chmod was called to set file permissions
+        mock_chmod.assert_any_call("/tmp/mock_cache", 0o755)
+
+
     def teardown(self):
         print("TEAR DOWN")