[MM-62687] Patch permission check to avoid modifying the system admin (#30292)

* [MM-62687] Patch permission check to avoid modifying the system admin

* Check for manage system first

* PR feedback

* Add another test

* Lint

* Fix test

server/channels/api4/user_test.go

@@ -4237,6 +4237,14 @@ func TestSetDefaultProfileImage(t *testing.T) {
 	_, err = th.SystemAdminClient.SetDefaultProfileImage(context.Background(), user.Id)
 	require.NoError(t, err)
 
+	// Check that a system admin can set the default profile image for another system admin
+	anotherAdmin := th.CreateUser()
+	_, appErr := th.App.UpdateUserRoles(th.Context, anotherAdmin.Id, model.SystemAdminRoleId+" "+model.SystemUserRoleId, false)
+	require.Nil(t, appErr)
+
+	_, err = th.SystemAdminClient.SetDefaultProfileImage(context.Background(), anotherAdmin.Id)
+	require.NoError(t, err)
+
 	ruser, appErr := th.App.GetUser(user.Id)
 	require.Nil(t, appErr)
 	assert.Less(t, ruser.LastPictureUpdate, iuser.LastPictureUpdate, "LastPictureUpdate should be updated to a lower negative number")

server/channels/app/authorization.go

@@ -202,7 +202,7 @@ func (a *App) SessionHasPermissionToUser(session model.Session, userID string) b
 	if userID == "" {
 		return false
 	}
-	if session.IsUnrestricted() {
+	if session.IsUnrestricted() || a.SessionHasPermissionTo(session, model.PermissionManageSystem) {
 		return true
 	}
 
@@ -210,11 +210,20 @@ func (a *App) SessionHasPermissionToUser(session model.Session, userID string) b
 		return true
 	}
 
-	if a.SessionHasPermissionTo(session, model.PermissionEditOtherUsers) {
+	if !a.SessionHasPermissionTo(session, model.PermissionEditOtherUsers) {
-		return true
+		return false
 	}
 
-	return false
+	user, err := a.GetUser(userID)
+	if err != nil {
+		return false
+	}
+
+	if user.IsSystemAdmin() {
+		return false
+	}
+
+	return true
 }
 
 func (a *App) SessionHasPermissionToUserOrBot(rctx request.CTX, session model.Session, userID string) bool {

server/channels/app/authorization_test.go

@@ -382,6 +382,7 @@ func TestSessionHasPermissionToUser(t *testing.T) {
 
 		th.AddPermissionToRole(model.PermissionEditOtherUsers.Id, model.SystemUserManagerRoleId)
 		assert.True(t, th.App.SessionHasPermissionToUser(session, th.BasicUser2.Id))
+		assert.False(t, th.App.SessionHasPermissionToUser(session, th.SystemAdminUser.Id))
 		th.RemovePermissionFromRole(model.PermissionEditOtherUsers.Id, model.SystemUserManagerRoleId)
 
 		bot, err := th.App.CreateBot(th.Context, &model.Bot{