Prevent a double free by not reentering be_tls_close().

Reentering this function with the right timing caused a double free,
typically crashing the backend.  By synchronizing a disconnection with
the authentication timeout, an unauthenticated attacker could achieve
this somewhat consistently.  Call be_tls_close() solely from within
proc_exit_prepare().  Back-patch to 9.0 (all supported versions).

Benkocs Norbert Attila

Security: CVE-2015-3165

1 files changed, 10 insertions, 1 deletions

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 6e2ba08a93d..87f543031ac 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -3960,7 +3960,16 @@ BackendInitialize(Port *port)
 	 * We arrange for a simple exit(1) if we receive SIGTERM or SIGQUIT or
 	 * timeout while trying to collect the startup packet.  Otherwise the
 	 * postmaster cannot shutdown the database FAST or IMMED cleanly if a
-	 * buggy client fails to send the packet promptly.
+	 * buggy client fails to send the packet promptly.  XXX it follows that
+	 * the remainder of this function must tolerate losing control at any
+	 * instant.  Likewise, any pg_on_exit_callback registered before or during
+	 * this function must be prepared to execute at any instant between here
+	 * and the end of this function.  Furthermore, affected callbacks execute
+	 * partially or not at all when a second exit-inducing signal arrives
+	 * after proc_exit_prepare() decrements on_proc_exit_index.  (Thanks to
+	 * that mechanic, callbacks need not anticipate more than one call.)  This
+	 * is fragile; it ought to instead follow the norm of handling interrupts
+	 * at selected, safe opportunities.
 	 */
 	pqsignal(SIGTERM, startup_die);
 	pqsignal(SIGQUIT, startup_die);