fix(cache): Do not change homedir for user that already exists (#399)

We used to update every part of the user information in the cache but
this can create problems if the admin changes the homedir configuration
on the broker side, since it would update the homedir parsing for the
user resulting in PAM creating a new one for the user at login.

UDENG-3125

internal/users/cache/db_test.go

@@ -114,6 +114,15 @@ func TestUpdateUserEntry(t *testing.T) {
 			// These values don't matter. We just want to make sure they are the same as the ones provided by the manager.
 			LastPwdChange: -1, MaxPwdAge: -1, PwdWarnPeriod: -1, PwdInactivity: -1, MinPwdAge: -1, ExpirationDate: -1,
 		},
+		"user1-new-homedir": {
+			Name:  "user1",
+			UID:   1111,
+			Gecos: "User1 gecos\nOn multiple lines",
+			Dir:   "/new/home/user1",
+			Shell: "/bin/bash",
+			// These values don't matter. We just want to make sure they are the same as the ones provided by the manager.
+			LastPwdChange: -1, MaxPwdAge: -1, PwdWarnPeriod: -1, PwdInactivity: -1, MinPwdAge: -1, ExpirationDate: -1,
+		},
 		"user1-without-gecos": {
 			Name:  "user1",
 			UID:   1111,
@@ -154,6 +163,7 @@ func TestUpdateUserEntry(t *testing.T) {
 
 		// User and Group renames
 		"Update user by changing attributes":                      {userCase: "user1-new-attributes", dbFile: "one_user_and_group"},
+		"Update user does not change homedir if it exists":        {userCase: "user1-new-homedir", dbFile: "one_user_and_group"},
 		"Update user by removing optional gecos field if not set": {userCase: "user1-without-gecos", dbFile: "one_user_and_group"},
 		"Update group by changing attributes":                     {groupCases: []string{"newgroup1"}, dbFile: "one_user_and_group"},
 

internal/users/cache/testdata/TestUpdateUserEntry/golden/update_user_by_changing_attributes

@@ -5,9 +5,9 @@ GroupByName:
 GroupToUsers:
     "11111": '{"GID":11111,"UIDs":[1111]}'
 UserByID:
-    "1111": '{"Name":"newuser1","UID":1111,"GID":11111,"Gecos":"New user1 gecos","Dir":"/home/newuser1","Shell":"/bin/dash","LastPwdChange":-1,"MaxPwdAge":-1,"PwdWarnPeriod":-1,"PwdInactivity":-1,"MinPwdAge":-1,"ExpirationDate":-1,"LastLogin":"ABCDETIME"}'
+    "1111": '{"Name":"newuser1","UID":1111,"GID":11111,"Gecos":"New user1 gecos","Dir":"/home/user1","Shell":"/bin/dash","LastPwdChange":-1,"MaxPwdAge":-1,"PwdWarnPeriod":-1,"PwdInactivity":-1,"MinPwdAge":-1,"ExpirationDate":-1,"LastLogin":"ABCDETIME"}'
 UserByName:
-    newuser1: '{"Name":"newuser1","UID":1111,"GID":11111,"Gecos":"New user1 gecos","Dir":"/home/newuser1","Shell":"/bin/dash","LastPwdChange":-1,"MaxPwdAge":-1,"PwdWarnPeriod":-1,"PwdInactivity":-1,"MinPwdAge":-1,"ExpirationDate":-1,"LastLogin":"ABCDETIME"}'
+    newuser1: '{"Name":"newuser1","UID":1111,"GID":11111,"Gecos":"New user1 gecos","Dir":"/home/user1","Shell":"/bin/dash","LastPwdChange":-1,"MaxPwdAge":-1,"PwdWarnPeriod":-1,"PwdInactivity":-1,"MinPwdAge":-1,"ExpirationDate":-1,"LastLogin":"ABCDETIME"}'
 UserToBroker:
     "1111": '"broker-id"'
 UserToGroups:

internal/users/cache/testdata/TestUpdateUserEntry/golden/update_user_does_not_change_homedir_if_it_exists

@@ -0,0 +1,14 @@
+GroupByID:
+    "11111": '{"Name":"group1","GID":11111}'
+GroupByName:
+    group1: '{"Name":"group1","GID":11111}'
+GroupToUsers:
+    "11111": '{"GID":11111,"UIDs":[1111]}'
+UserByID:
+    "1111": '{"Name":"user1","UID":1111,"GID":11111,"Gecos":"User1 gecos\nOn multiple lines","Dir":"/home/user1","Shell":"/bin/bash","LastPwdChange":-1,"MaxPwdAge":-1,"PwdWarnPeriod":-1,"PwdInactivity":-1,"MinPwdAge":-1,"ExpirationDate":-1,"LastLogin":"ABCDETIME"}'
+UserByName:
+    user1: '{"Name":"user1","UID":1111,"GID":11111,"Gecos":"User1 gecos\nOn multiple lines","Dir":"/home/user1","Shell":"/bin/bash","LastPwdChange":-1,"MaxPwdAge":-1,"PwdWarnPeriod":-1,"PwdInactivity":-1,"MinPwdAge":-1,"ExpirationDate":-1,"LastLogin":"ABCDETIME"}'
+UserToBroker:
+    "1111": '"broker-id"'
+UserToGroups:
+    "1111": '{"UID":1111,"GIDs":[11111]}'

internal/users/cache/update.go

@@ -63,6 +63,12 @@ func updateUser(buckets map[string]bucketWithName, userContent userDB) {
 		_ = buckets[userByNameBucketName].Delete([]byte(existingUser.Name)) // No error as we are not in a RO transaction.
 	}
 
+	// Ensure that we use the same homedir as the one we have in cache.
+	if existingUser.Dir != "" && existingUser.Dir != userContent.Dir {
+		slog.Warn(fmt.Sprintf("User %q already has a homedir. The existing %q one will be kept instead of %q", userContent.Name, existingUser.Dir, userContent.Dir))
+		userContent.Dir = existingUser.Dir
+	}
+
 	// Update user buckets
 	updateBucket(buckets[userByIDBucketName], userContent.UID, userContent)
 	updateBucket(buckets[userByNameBucketName], userContent.Name, userContent)