90_localscan_dlopen.dpatch

Description: Allow one to use and switch between different local_scan functions
 without recompiling exim.
 http://marc.merlins.org/linux/exim/files/sa-exim-current/ Original patch from
 David Woodhouse, modified first by Derrick 'dman' Hudson and then by Marc
 MERLIN for SA-Exim and minor/major API version tracking
Author: David Woodhouse, Derrick 'dman' Hudson, Marc MERLIN
Origin: other, http://marc.merlins.org/linux/exim/files/sa-exim-current/
Forwarded: no
Last-Update: 2018-12-12

--- a/src/EDITME
+++ b/src/EDITME
@@ -824,6 +824,21 @@ HEADERS_CHARSET="ISO-8859-1"
 
 
 #------------------------------------------------------------------------------
+# On systems which support dynamic loading of shared libraries, Exim can
+# load a local_scan function specified in its config file instead of having
+# to be recompiled with the desired local_scan function. For a full
+# description of the API to this function, see the Exim specification.
+
+DLOPEN_LOCAL_SCAN=yes
+
+# If you set DLOPEN_LOCAL_SCAN, then you need to include -rdynamic in the
+# linker flags.  Without it, the loaded .so won't be able to access any
+# functions from exim.
+
+LDFLAGS += -rdynamic
+CFLAGS += -fvisibility=hidden
+
+#------------------------------------------------------------------------------
 # The default distribution of Exim contains only the plain text form of the
 # documentation. Other forms are available separately. If you want to install
 # the documentation in "info" format, first fetch the Texinfo documentation
--- a/src/config.h.defaults
+++ b/src/config.h.defaults
@@ -32,6 +32,8 @@ Do not put spaces between # and the 'def
 
 #define AUTH_VARS                     3
 
+#define DLOPEN_LOCAL_SCAN
+
 #define BIN_DIRECTORY
 
 #define CONFIGURE_FILE
--- a/src/globals.c
+++ b/src/globals.c
@@ -141,6 +141,10 @@ int     dsn_ret                = 0;
 const pcre  *regex_DSN         = NULL;
 uschar *dsn_advertise_hosts    = NULL;
 
+#ifdef DLOPEN_LOCAL_SCAN
+uschar *local_scan_path        = NULL;
+#endif
+
 #ifdef SUPPORT_TLS
 BOOL    gnutls_compat_mode     = FALSE;
 BOOL    gnutls_allow_auto_pkcs11 = FALSE;
--- a/src/globals.h
+++ b/src/globals.h
@@ -138,6 +138,9 @@ extern int      dsn_ret;               /
 extern const pcre  *regex_DSN;         /* For recognizing DSN settings */
 extern uschar  *dsn_advertise_hosts;   /* host for which TLS is advertised */
 
+#ifdef DLOPEN_LOCAL_SCAN
+extern uschar *local_scan_path;        /* Path to local_scan() library */
+#endif
 /* Input-reading functions for messages, so we can use special ones for
 incoming TCP/IP. */
 
--- a/src/local_scan.c
+++ b/src/local_scan.c
@@ -5,61 +5,131 @@
 /* Copyright (c) University of Cambridge 1995 - 2009 */
 /* See the file NOTICE for conditions of use and distribution. */
 
+#include "exim.h"
 
-/******************************************************************************
-This file contains a template local_scan() function that just returns ACCEPT.
-If you want to implement your own version, you should copy this file to, say
-Local/local_scan.c, and edit the copy. To use your version instead of the
-default, you must set
-
-HAVE_LOCAL_SCAN=yes
-LOCAL_SCAN_SOURCE=Local/local_scan.c
-
-in your Local/Makefile. This makes it easy to copy your version for use with
-subsequent Exim releases.
-
-For a full description of the API to this function, see the Exim specification.
-******************************************************************************/
-
-
-/* This is the only Exim header that you should include. The effect of
-including any other Exim header is not defined, and may change from release to
-release. Use only the documented interface! */
-
-#include "local_scan.h"
-
-
-/* This is a "do-nothing" version of a local_scan() function. The arguments
-are:
-
-  fd             The file descriptor of the open -D file, which contains the
-                   body of the message. The file is open for reading and
-                   writing, but modifying it is dangerous and not recommended.
-
-  return_text    A pointer to an unsigned char* variable which you can set in
-                   order to return a text string. It is initialized to NULL.
-
-The return values of this function are:
-
-  LOCAL_SCAN_ACCEPT
-                 The message is to be accepted. The return_text argument is
-                   saved in $local_scan_data.
-
-  LOCAL_SCAN_REJECT
-                 The message is to be rejected. The returned text is used
-                   in the rejection message.
-
-  LOCAL_SCAN_TEMPREJECT
-                 This specifies a temporary rejection. The returned text
-                   is used in the rejection message.
-*/
+#ifdef DLOPEN_LOCAL_SCAN
+#include <dlfcn.h>
+static int (*local_scan_fn)(int fd, uschar **return_text) = NULL;
+static int load_local_scan_library(void);
+#endif
 
 int
 local_scan(int fd, uschar **return_text)
 {
 fd = fd;                      /* Keep picky compilers happy */
 return_text = return_text;
-return LOCAL_SCAN_ACCEPT;
+#ifdef DLOPEN_LOCAL_SCAN
+/* local_scan_path is defined AND not the empty string */
+if (local_scan_path && *local_scan_path)
+  {
+  if (!local_scan_fn)
+    {
+    if (!load_local_scan_library())
+      {
+        char *base_msg , *error_msg , *final_msg ;
+        int final_length = -1 ;
+
+        base_msg=US"Local configuration error - local_scan() library failure\n";
+        error_msg = dlerror() ;
+
+        final_length = strlen(base_msg) + strlen(error_msg) + 1 ;
+        final_msg = (char*)malloc( final_length*sizeof(char) ) ;
+        *final_msg = '\0' ;
+
+        strcat( final_msg , base_msg ) ;
+        strcat( final_msg , error_msg ) ;
+
+        *return_text = final_msg ;
+      return LOCAL_SCAN_TEMPREJECT;
+      }
+    }
+    return local_scan_fn(fd, return_text);
+  }
+else
+#endif
+  return LOCAL_SCAN_ACCEPT;
+}
+
+#ifdef DLOPEN_LOCAL_SCAN
+
+static int load_local_scan_library(void)
+{
+/* No point in keeping local_scan_lib since we'll never dlclose() anyway */
+void *local_scan_lib = NULL;
+int (*local_scan_version_fn)(void);
+int vers_maj;
+int vers_min;
+
+local_scan_lib = dlopen(local_scan_path, RTLD_NOW);
+if (!local_scan_lib)
+  {
+  log_write(0, LOG_MAIN|LOG_REJECT, "local_scan() library open failed - "
+    "message temporarily rejected");
+  return FALSE;
+  }
+
+local_scan_version_fn = dlsym(local_scan_lib, "local_scan_version_major");
+if (!local_scan_version_fn)
+  {
+  dlclose(local_scan_lib);
+  log_write(0, LOG_MAIN|LOG_REJECT, "local_scan() library doesn't contain "
+    "local_scan_version_major() function - message temporarily rejected");
+  return FALSE;
+  }
+
+/* The major number is increased when the ABI is changed in a non
+   backward compatible way. */
+vers_maj = local_scan_version_fn();
+
+local_scan_version_fn = dlsym(local_scan_lib, "local_scan_version_minor");
+if (!local_scan_version_fn)
+  {
+  dlclose(local_scan_lib);
+  log_write(0, LOG_MAIN|LOG_REJECT, "local_scan() library doesn't contain "
+    "local_scan_version_minor() function - message temporarily rejected");
+  return FALSE;
+  }
+
+/* The minor number is increased each time a new feature is added (in a
+   way that doesn't break backward compatibility) -- Marc */
+vers_min = local_scan_version_fn();
+
+
+if (vers_maj != LOCAL_SCAN_ABI_VERSION_MAJOR)
+  {
+  dlclose(local_scan_lib);
+  local_scan_lib = NULL;
+  log_write(0, LOG_MAIN|LOG_REJECT, "local_scan() has an incompatible major"
+    "version number, you need to recompile your module for this version"
+    "of exim (The module was compiled for version %d.%d and this exim provides"
+    "ABI version %d.%d)", vers_maj, vers_min, LOCAL_SCAN_ABI_VERSION_MAJOR,
+    LOCAL_SCAN_ABI_VERSION_MINOR);
+  return FALSE;
+  }
+else if (vers_min > LOCAL_SCAN_ABI_VERSION_MINOR)
+  {
+  dlclose(local_scan_lib);
+  local_scan_lib = NULL;
+  log_write(0, LOG_MAIN|LOG_REJECT, "local_scan() has an incompatible minor"
+    "version number, you need to recompile your module for this version"
+    "of exim (The module was compiled for version %d.%d and this exim provides"
+    "ABI version %d.%d)", vers_maj, vers_min, LOCAL_SCAN_ABI_VERSION_MAJOR,
+    LOCAL_SCAN_ABI_VERSION_MINOR);
+  return FALSE;
+  }
+
+local_scan_fn = dlsym(local_scan_lib, "local_scan");
+if (!local_scan_fn)
+  {
+  dlclose(local_scan_lib);
+  log_write(0, LOG_MAIN|LOG_REJECT, "local_scan() library doesn't contain "
+    "local_scan() function - message temporarily rejected");
+  return FALSE;
+  }
+
+return TRUE;
 }
 
+#endif /* DLOPEN_LOCAL_SCAN */
+
 /* End of local_scan.c */
--- a/src/local_scan.h
+++ b/src/local_scan.h
@@ -17,6 +17,7 @@ settings, and the store functions. */
 
 #include <stdarg.h>
 #include <sys/types.h>
+#pragma GCC visibility push(default)
 #include "config.h"
 #include "mytypes.h"
 #include "store.h"
@@ -192,4 +193,6 @@ extern uschar *string_copy(const uschar
 extern uschar *string_copyn(const uschar *, int);
 extern uschar *string_sprintf(const char *, ...) ALMOST_PRINTF(1,2);
 
+#pragma GCC visibility pop
+
 /* End of local_scan.h */
--- a/src/readconf.c
+++ b/src/readconf.c
@@ -199,6 +199,9 @@ static optionlist optionlist_config[] =
   { "local_from_prefix",        opt_stringptr,   &local_from_prefix },
   { "local_from_suffix",        opt_stringptr,   &local_from_suffix },
   { "local_interfaces",         opt_stringptr,   &local_interfaces },
+#ifdef DLOPEN_LOCAL_SCAN
+  { "local_scan_path",          opt_stringptr,   &local_scan_path },
+#endif
 #ifdef HAVE_LOCAL_SCAN
   { "local_scan_timeout",       opt_time,        &local_scan_timeout },
 #endif