Prevent show_session_authorization from crashing when session_authorization

hasn't been set.

The only known case where this can happen is when show_session_authorization
is invoked in an autovacuum process, which is possible if an index function
calls it, as for example in bug #5669 from Andrew Geery.  We could perhaps
try to return a sensible value, such as the name of the cluster-owning
superuser; but that seems like much more trouble than the case is worth,
and in any case it could create new possible failure modes.  Simply
returning an empty string seems like the most appropriate fix.

Back-patch to all supported versions, even those before autovacuum, just
in case there's another way to provoke this crash.

diff --git a/src/backend/commands/variable.c b/src/backend/commands/variable.c
index 835b548235e718e923cbcb6ceb9bc298e1745839..c078443c5e0d8272dde8762bca9ec4068cc7ebd4 100644 (file)
--- a/src/backend/commands/variable.c
+++ b/src/backend/commands/variable.c
@@ -771,6 +771,10 @@ show_session_authorization(void)
        Oid                     savedoid;
        char       *endptr;
 
+       /* If session_authorization hasn't been set in this process, return "" */
+       if (value == NULL || value[0] == '\0')
+               return "";
+
        Assert(strspn(value, "x") == NAMEDATALEN &&
                   (value[NAMEDATALEN] == 'T' || value[NAMEDATALEN] == 'F'));