Make LOAD of an already-loaded library into a no-op, instead of attempting

to unload and re-load the library.

The difficulty with unloading a library is that we haven't defined safe
protocols for doing so.  In particular, there's no safe mechanism for
getting out of a "hook" function pointer unless libraries are unloaded
in reverse order of loading.  And there's no mechanism at all for undefining
a custom GUC variable, so GUC would be left with a pointer to an old value
that might or might not still be valid, and very possibly wouldn't be in
the same place anymore.

While the unload and reload behavior had some usefulness in easing
development of new loadable libraries, it's of no use whatever to normal
users, so just disabling it isn't giving up that much.  Someday we might
care to expend the effort to develop safe unload protocols; but even if
we did, there'd be little certainty that every third-party loadable module
was following them, so some security restrictions would still be needed.

Back-patch to 8.2; before that, LOAD was superuser-only anyway.

Security: unprivileged users could crash backend.  CVE not assigned yet

diff --git a/doc/src/sgml/ref/create_function.sgml b/doc/src/sgml/ref/create_function.sgml
index 70baae396e1d83c617f02a2e95c6d44ca59e6efe..09083d66ec8e60041fa10ad93c3333738964899e 100644 (file)
--- a/doc/src/sgml/ref/create_function.sgml
+++ b/doc/src/sgml/ref/create_function.sgml
@@ -528,8 +528,7 @@ CREATE FUNCTION foo(int, int default 42) ...
     When repeated <command>CREATE FUNCTION</command> calls refer to
     the same object file, the file is only loaded once per session.
     To unload and
-    reload the file (perhaps during development), use the <xref
-    linkend="sql-load" endterm="sql-load-title"> command.
+    reload the file (perhaps during development), start a new session.
    </para>
 
    <para>

diff --git a/doc/src/sgml/ref/load.sgml b/doc/src/sgml/ref/load.sgml
index be370fa823276c5d87453278afa4371c06ea270a..76b1104aaffa013b98d460ccc644cab88b0c82b2 100644 (file)
--- a/doc/src/sgml/ref/load.sgml
+++ b/doc/src/sgml/ref/load.sgml
@@ -11,7 +11,7 @@ $PostgreSQL$
 
  <refnamediv>
   <refname>LOAD</refname>
-  <refpurpose>load or reload a shared library file</refpurpose>
+  <refpurpose>load a shared library file</refpurpose>
  </refnamediv>
 
  <indexterm zone="sql-load">
@@ -29,13 +29,12 @@ LOAD '<replaceable class="PARAMETER">filename</replaceable>'
 
   <para>
    This command loads a shared library file into the <productname>PostgreSQL</>
-   server's address space.  If the file had been loaded previously,
-   it is first unloaded.  This command is primarily useful to unload
-   and reload a shared library file that has been changed since the
-   server first loaded it.  To make use of the shared library,
-   function(s) in it need to be declared using the <xref
-   linkend="sql-createfunction" endterm="sql-createfunction-title">
-   command.
+   server's address space.  If the file has been loaded already,
+   the command does nothing.  Shared library files that contain C functions
+   are automatically loaded whenever one of their functions is called.
+   Therefore, an explicit <command>LOAD</> is usually only needed to
+   load a library that modifies the server's behavior through <quote>hooks</>
+   rather than providing a set of functions.
   </para>
 
   <para>

diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml
index 3c8ce438ebbcfc3fe55ef62fb432be0becc13ad5..b340e2ffe24b6cb428185ad6af0b9547dc4e7840 100644 (file)
--- a/doc/src/sgml/xfunc.sgml
+++ b/doc/src/sgml/xfunc.sgml
@@ -1481,9 +1481,7 @@ PG_MODULE_MAGIC;
     file is retained in memory.  Future calls in the same session to
     the function(s) in that file will only incur the small overhead of
     a symbol table lookup.  If you need to force a reload of an object
-    file, for example after recompiling it, use the <xref
-    linkend="sql-load" endterm="sql-load-title"> command or begin a
-    fresh session.
+    file, for example after recompiling it, begin a fresh session.
    </para>
 
    <indexterm zone="xfunc-c-dynload">
@@ -1509,8 +1507,8 @@ PG_MODULE_MAGIC;
     unloading the file.  Likewise, the function receives no parameters and
     should return void.  Note that <function>_PG_fini</> will only be called
     during an unload of the file, not during process termination.
-    (Presently, an unload only happens in the context of re-loading
-    the file due to an explicit <command>LOAD</> command.)
+    (Presently, unloads are disabled and will never occur, but this may
+    change in the future.)
    </para>
 
   </sect2>

diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index c435944bb2af07743703c3badf31123ad4e8afdf..529940c23baf5b6c4bc86ed5cdae337de51b7b15 100644 (file)
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -385,10 +385,17 @@ incompatible_module_error(const char *libname,
  * Unload the specified dynamic-link library file, if it is loaded.
  *
  * Note: libname is expected to be an exact name for the library file.
+ *
+ * XXX for the moment, this is disabled, resulting in LOAD of an already-loaded
+ * library always being a no-op.  We might re-enable it someday if we can
+ * convince ourselves we have safe protocols for un-hooking from hook function
+ * pointers, releasing custom GUC variables, and perhaps other things that
+ * are definitely unsafe currently.
  */
 static void
 internal_unload_library(const char *libname)
 {
+#ifdef NOT_USED
        DynamicFileList *file_scanner,
                           *prv,
                           *nxt;
@@ -436,6 +443,7 @@ internal_unload_library(const char *libname)
                else
                        prv = file_scanner;
        }
+#endif /* NOT_USED */
 }
 
 static bool