Restore PGREQUIRESSL recognition in libpq.

Commit 65c3bf19 moved handling of the,
already then, deprecated requiressl parameter into conninfo_storeval().
The default PGREQUIRESSL environment variable was however lost in the
change resulting in a potentially silent accept of a non-SSL connection
even when set.  Its documentation remained.  Restore its implementation.
Also amend the documentation to mark PGREQUIRESSL as deprecated for
those not following the link to requiressl.  Back-patch to 9.3, where
commit 65c3bf19 first appeared.

Behavior has been more complex when the user provides both deprecated
and non-deprecated settings.  Before commit 65c3bf19, libpq operated
according to the first of these found:

  requiressl=1
  PGREQUIRESSL=1
  sslmode=*
  PGSSLMODE=*

(Note requiressl=0 didn't override sslmode=*; it would only suppress
PGREQUIRESSL=1 or a previous requiressl=1.  PGREQUIRESSL=0 had no effect
whatsoever.)  Starting with commit 65c3bf19, libpq ignored PGREQUIRESSL,
and order of precedence changed to this:

  last of requiressl=* or sslmode=*
  PGSSLMODE=*

Starting now, adopt the following order of precedence:

  last of requiressl=* or sslmode=*
  PGSSLMODE=*
  PGREQUIRESSL=1

This retains the 65c3bf19 behavior for connection strings that contain
both requiressl=* and sslmode=*.  It retains the 65c3bf19 change that
either connection string option overrides both environment variables.
For the first time, PGSSLMODE has precedence over PGREQUIRESSL; this
avoids reducing security of "PGREQUIRESSL=1 PGSSLMODE=verify-full"
configurations originating under v9.3 and later.

Daniel Gustafsson

Security: CVE-2017-7485

doc/src/sgml/libpq.sgml

@@ -7061,6 +7061,9 @@ myEventProc(PGEventId evtId, void *evtInfo, void *passThrough)
       </indexterm>
       <envar>PGREQUIRESSL</envar> behaves the same as the <xref
       linkend="libpq-connect-requiressl"> connection parameter.
+      This environment variable is deprecated in favor of the
+      <envar>PGSSLMODE</envar> variable; setting both variables suppresses the
+      effect of this one.
      </para>
     </listitem>
 

src/interfaces/libpq/fe-connect.c

@@ -5083,6 +5083,30 @@ conninfo_add_defaults(PQconninfoOption *options, PQExpBuffer errorMessage)
 			}
 		}
 
+		/*
+		 * Interpret the deprecated PGREQUIRESSL environment variable.  Per
+		 * tradition, translate values starting with "1" to sslmode=require,
+		 * and ignore other values.  Given both PGREQUIRESSL=1 and PGSSLMODE,
+		 * PGSSLMODE takes precedence; the opposite was true before v9.3.
+		 */
+		if (strcmp(option->keyword, "sslmode") == 0)
+		{
+			const char *requiresslenv = getenv("PGREQUIRESSL");
+
+			if (requiresslenv != NULL && requiresslenv[0] == '1')
+			{
+				option->val = strdup("require");
+				if (!option->val)
+				{
+					if (errorMessage)
+						printfPQExpBuffer(errorMessage,
+										  libpq_gettext("out of memory\n"));
+					return false;
+				}
+				continue;
+			}
+		}
+
 		/*
 		 * No environment variable specified or the variable isn't set - try
 		 * compiled-in default