From 79fae02a1c621ca7b476dda8194e3bf24f177c89 Mon Sep 17 00:00:00 2001

From: Paul Jakma <paul@jakma.org>

Date: Sat, 6 Jan 2018 19:52:10 +0000

Subject: [PATCH] bgpd/security: Fix double free of unknown attribute

Security issue: Quagga-2018-1114

See: https://www.quagga.net/security/Quagga-2018-1114.txt

It is possible for bgpd to double-free an unknown attribute. This can happen

via bgp_update_receive receiving an UPDATE with an invalid unknown attribute.

bgp_update_receive then will call bgp_attr_unintern_sub and bgp_attr_flush,

and the latter may try free an already freed unknown attr.

* bgpd/bgp_attr.c: (transit_unintern) Take a pointer to the caller's storage

  for the (struct transit *), so that transit_unintern can NULL out the

  caller's reference if the (struct transit) is freed.

  (cluster_unintern) By inspection, appears to have a similar issue.

  (bgp_attr_unintern_sub) adjust for above.

---

 bgpd/bgp_attr.c | 33 +++++++++++++++++++--------------

 bgpd/bgp_attr.h |  4 ++--

 2 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/bgpd/bgp_attr.c b/bgpd/bgp_attr.c

index cbf2902d..8eea4ed0 100644

--- a/bgpd/bgp_attr.c

+++ b/bgpd/bgp_attr.c

@@ -183,15 +183,17 @@ cluster_intern (struct cluster_list *cluster)

 }

 void

-cluster_unintern (struct cluster_list *cluster)

+cluster_unintern (struct cluster_list **cluster)

 {

-  if (cluster->refcnt)

-    cluster->refcnt--;

+  struct cluster_list *c = *cluster;

+  if (c->refcnt)

+    c->refcnt--;

-  if (cluster->refcnt == 0)

+  if (c->refcnt == 0)

     {

-      hash_release (cluster_hash, cluster);

-      cluster_free (cluster);

+      hash_release (cluster_hash, c);

+      cluster_free (c);

+      *cluster = NULL;

     }

 }

@@ -241,15 +243,18 @@ transit_intern (struct transit *transit)

 }

 void

-transit_unintern (struct transit *transit)

+transit_unintern (struct transit **transit)

 {

-  if (transit->refcnt)

-    transit->refcnt--;

+  struct transit *t = *transit;

+  

+  if (t->refcnt)

+    t->refcnt--;

-  if (transit->refcnt == 0)

+  if (t->refcnt == 0)

     {

-      hash_release (transit_hash, transit);

-      transit_free (transit);

+      hash_release (transit_hash, t);

+      transit_free (t);

+      *transit = NULL;

     }

 }

@@ -658,11 +663,11 @@ bgp_attr_unintern_sub (struct attr *attr)

       UNSET_FLAG(attr->flag, BGP_ATTR_EXT_COMMUNITIES);

       if (attr->extra->cluster)

-        cluster_unintern (attr->extra->cluster);

+        cluster_unintern (&attr->extra->cluster);

       UNSET_FLAG(attr->flag, BGP_ATTR_CLUSTER_LIST);

       if (attr->extra->transit)

-        transit_unintern (attr->extra->transit);

+        transit_unintern (&attr->extra->transit);

     }

 }

diff --git a/bgpd/bgp_attr.h b/bgpd/bgp_attr.h

index df87c863..7d3cc64b 100644

--- a/bgpd/bgp_attr.h

+++ b/bgpd/bgp_attr.h

@@ -174,10 +174,10 @@ extern unsigned long int attr_unknown_count (void);

 /* Cluster list prototypes. */

 extern int cluster_loop_check (struct cluster_list *, struct in_addr);

-extern void cluster_unintern (struct cluster_list *);

+extern void cluster_unintern (struct cluster_list **);

 /* Transit attribute prototypes. */

-void transit_unintern (struct transit *);

+void transit_unintern (struct transit **);

 /* Below exported for unit-test purposes only */

 struct bgp_attr_parser_args {

-- 

2.14.3