Implement -D filtering, first pass.

6 files changed, 144 insertions, 3 deletions

diff --git a/src/src/EDITME b/src/src/EDITME
index 1ae139944..d093eb690 100644
--- a/src/src/EDITME
+++ b/src/src/EDITME
@@ -494,6 +494,31 @@ FIXED_NEVER_USERS=root
 
 
 #------------------------------------------------------------------------------
+# By contrast, you might be maintaining a system which relies upon the ability
+# to override values with -D and assumes that these will be passed through to
+# the delivery processes.  As of Exim 4.73, this is no longer the case by
+# default.  Going forward, we strongly recommend that you use a shim Exim
+# configuration file owned by root stored under TRUSTED_CONFIG_PREFIX_LIST.
+# That shim can set macros before .include'ing your main configuration file.
+#
+# As a strictly transient measure to ease migration to 4.73, the
+# WHITELIST_D_MACROS value definies a colon-separated list of macro-names
+# which are permitted to be overriden from the command-line which will be
+# honoured by the Exim user.  So these are macros that can persist to delivery
+# time.
+# Examples might be -DTLS or -DSPOOL=/some/dir.  The values on the
+# command-line are filtered to only permit: [A-Za-z0-9_/.-]*
+#
+# This option is highly likely to be removed in a future release.  It exists
+# only to make 4.73 as easy as possible to migrate to.  If you use it, we
+# encourage you to schedule time to rework your configuration to not depend
+# upon it.  Most people should not need to use this.
+#
+# By default, no macros are whitelisted for -D usage.
+
+# WHITELIST_D_MACROS=TLS:SPOOL
+
+#------------------------------------------------------------------------------
 # Exim has support for the AUTH (authentication) extension of the SMTP
 # protocol, as defined by RFC 2554. If you don't know what SMTP authentication
 # is, you probably won't want to include this code, so you should leave these
diff --git a/src/src/buildconfig.c b/src/src/buildconfig.c
index 7e2790bb8..49d8c411a 100644
--- a/src/src/buildconfig.c
+++ b/src/src/buildconfig.c
@@ -800,11 +800,13 @@ while (fgets(buffer, sizeof(buffer), base) != NULL)
         fprintf(new, "\"%s\"\n", value);
         }
 
-      /* Timezone values HEADERS_CHARSET, and TCP_WRAPPERS_DAEMON_NAME get quoted */
+      /* Timezone values HEADERS_CHARSET, TCP_WRAPPERS_DAEMON_NAME and
+      WHITELIST_D_MACROS get quoted */
 
       else if (strcmp(name, "TIMEZONE_DEFAULT") == 0||
                strcmp(name, "TCP_WRAPPERS_DAEMON_NAME") == 0||
-               strcmp(name, "HEADERS_CHARSET") == 0)
+               strcmp(name, "HEADERS_CHARSET") == 0||
+	       strcmp(name, "WHITELIST_D_MACROS") == 0)
         fprintf(new, "\"%s\"\n", value);
 
       /* For others, quote any paths and don't quote anything else */
diff --git a/src/src/config.h.defaults b/src/src/config.h.defaults
index d3d7d65bb..b4e2c6d9c 100644
--- a/src/src/config.h.defaults
+++ b/src/src/config.h.defaults
@@ -145,6 +145,8 @@ it's a default value. */
 #define USE_TCP_WRAPPERS
 #define USE_TDB
 
+#define WHITELIST_D_MACROS
+
 #define WITH_CONTENT_SCAN
 #define WITH_OLD_DEMIME
 #define WITH_OLD_CLAMAV_STREAM
diff --git a/src/src/exim.c b/src/src/exim.c
index 729114c1c..f50a62b94 100644
--- a/src/src/exim.c
+++ b/src/src/exim.c
@@ -1132,6 +1132,102 @@ exit(EXIT_FAILURE);
 
 
 /*************************************************
+*    Validate that the macros given are okay     *
+*************************************************/
+
+/* Typically, Exim will drop privileges if macros are supplied.  In some
+cases, we want to not do so.
+
+Arguments:    none (macros is a global)
+Returns:      true if trusted, false otherwise
+*/
+
+static BOOL
+macros_trusted(void)
+{
+#ifdef WHITELIST_D_MACROS
+macro_item *m;
+uschar *whitelisted, *end, *p, **whites, **w;
+int white_count, i, n;
+size_t len;
+BOOL prev_char_item, found;
+#endif
+
+if (macros == NULL)
+  return TRUE;
+#ifndef WHITELIST_D_MACROS
+return FALSE;
+#else
+
+/* Get a list of macros which are whitelisted */
+whitelisted = string_copy_malloc(US WHITELIST_D_MACROS);
+prev_char_item = FALSE;
+white_count = 0;
+for (p = whitelisted; *p != '\0'; ++p)
+  {
+  if (*p == ':' || isspace(*p))
+    {
+    *p = '\0';
+    if (prev_char_item)
+      ++white_count;
+    prev_char_item = FALSE;
+    continue;
+    }
+  if (!prev_char_item)
+    prev_char_item = TRUE;
+  }
+end = p;
+if (prev_char_item)
+  ++white_count;
+if (!white_count)
+  return FALSE;
+whites = store_malloc(sizeof(uschar *) * (white_count+1));
+for (p = whitelisted, i = 0; (p != end) && (i < white_count); ++p)
+  {
+  if (*p != '\0')
+    {
+    whites[i++] = p;
+    if (i == white_count)
+      break;
+    while (*p != '\0' && p < end)
+      ++p;
+    }
+  }
+whites[i] = NULL;
+
+/* The list of macros should be very short.  Accept the N*M complexity. */
+for (m = macros; m != NULL; m = m->next)
+  {
+  found = FALSE;
+  for (w = whites; *w; ++w)
+    if (Ustrcmp(*w, m->name) == 0)
+      {
+      found = TRUE;
+      break;
+      }
+  if (!found)
+    return FALSE;
+  if (m->replacement == NULL)
+    continue;
+  len = Ustrlen(m->replacement);
+  if (len == 0)
+    continue;
+  n = pcre_exec(regex_whitelisted_macro, NULL, CS m->replacement, len,
+   0, PCRE_EOPT, NULL, 0);
+  if (n < 0)
+    {
+    if (n != PCRE_ERROR_NOMATCH)
+      debug_printf("macros_trusted checking %s returned %d\n", m->name, n);
+    return FALSE;
+    }
+  }
+debug_printf("macros_trusted overriden to true by whitelisting\n");
+return TRUE;
+#endif
+}
+
+
+/*************************************************
 *          Entry point and high-level code       *
 *************************************************/
 
@@ -1417,6 +1513,15 @@ regex_smtp_code =
   regex_must_compile(US"^\\d\\d\\d\\s(?:\\d\\.\\d\\d?\\d?\\.\\d\\d?\\d?\\s)?",
     FALSE, TRUE);
 
+#ifdef WHITELIST_D_MACROS
+/* Precompile the regular expression used to filter the content of macros
+given to -D for permissibility. */
+
+regex_whitelisted_macro =
+  regex_must_compile(US"^[A-Za-z0-9_/.-]*$", FALSE, TRUE);
+#endif
+
+
 /* If the program is called as "mailq" treat it as equivalent to "exim -bp";
 this seems to be a generally accepted convention, since one finds symbolic
 links called "mailq" in standard OS configurations. */
@@ -3145,7 +3250,8 @@ values (such as the path name). If running in the test harness, pretend that
 configuration file changes and macro definitions haven't happened. */
 
 if ((                                            /* EITHER */
-    (!trusted_config || macros != NULL) &&       /* Config changed, and */
+    (!trusted_config ||                          /* Config changed, or */
+     !macros_trusted()) &&                       /*  impermissible macros and */
     real_uid != root_uid &&                      /* Not root, and */
     !running_in_test_harness                     /* Not fudged */
     ) ||                                         /*   OR   */
diff --git a/src/src/globals.c b/src/src/globals.c
index 500691cb0..71de52aac 100644
--- a/src/src/globals.c
+++ b/src/src/globals.c
@@ -930,6 +930,9 @@ const pcre *regex_PIPELINING   = NULL;
 const pcre *regex_SIZE         = NULL;
 const pcre *regex_smtp_code    = NULL;
 const pcre *regex_ismsgid      = NULL;
+#ifdef WHITELIST_D_MACROS
+const pcre *regex_whitelisted_macro = NULL;
+#endif
 #ifdef WITH_CONTENT_SCAN
 uschar *regex_match_string     = NULL;
 #endif
diff --git a/src/src/globals.h b/src/src/globals.h
index 62dd6b04a..b4e3f2a6c 100644
--- a/src/src/globals.h
+++ b/src/src/globals.h
@@ -594,6 +594,9 @@ extern const pcre  *regex_PIPELINING;  /* For recognizing PIPELINING */
 extern const pcre  *regex_SIZE;        /* For recognizing SIZE settings */
 extern const pcre  *regex_smtp_code;   /* For recognizing SMTP codes */
 extern const pcre  *regex_ismsgid;     /* Compiled r.e. for message it */
+#ifdef WHITELIST_D_MACROS
+extern const pcre  *regex_whitelisted_macro; /* For -D macro values */
+#endif
 #ifdef WITH_CONTENT_SCAN
 extern uschar *regex_match_string;     /* regex that matched a line (regex ACL condition) */
 #endif