From d3434960842a8405a4fd4e2e7b43f2f4a7075a0b Mon Sep 17 00:00:00 2001
From: James Turner <zakalawe@mac.com>
Date: Thu, 26 Jan 2017 20:35:25 +0000
Subject: [PATCH] Check nav-cache write-ability explicitly.

Check the file permissions before opening using the new SGPath APIs,
and validate the result using Sqlite APIs after opening.
---
 src/Navaids/NavDataCache.cxx | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/Navaids/NavDataCache.cxx b/src/Navaids/NavDataCache.cxx
index 4c919bc95..efe600e76 100644
--- a/src/Navaids/NavDataCache.cxx
+++ b/src/Navaids/NavDataCache.cxx
@@ -261,6 +261,9 @@ public:
       SG_LOG(SG_NAVCACHE, SG_INFO, "NavCache at:" << path);
 
       readOnly = fgGetBool("/sim/fghome-readonly", false);
+      if (!readOnly && !path.canWrite()) {
+          throw sg_exception("Nav-cache file is not writeable");
+      }
 
       int openFlags = readOnly ? SQLITE_OPEN_READONLY :
         SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE;
@@ -276,6 +279,10 @@ public:
           throw sg_exception("Navcache failed to open:" + errMsg);
       }
 
+      if (!readOnly && (sqlite3_db_readonly(db, nullptr) != 0)) {
+          throw sg_exception("Nav-cache file opened but is not writeable");
+      }
+
     sqlite3_stmt_ptr checkTables =
       prepare("SELECT count(*) FROM sqlite_master WHERE name='properties'");