Merge branch 'maint-0.4.8'

changes/bug40897

@@ -0,0 +1,6 @@
+  o Major bugfixes (TROVE-2023-007, exit):
+    - Improper error propagation from a safety check in conflux leg
+      linking lead to a desynchronization of which legs were part of
+      a conflux set, ultimately causing a UAF and NULL pointer
+      dereference crash on Exit relays. Fixes bug 40897;
+      bugfix on 0.4.8.1-alpha.

src/core/or/conflux.c

@@ -115,6 +115,8 @@ conflux_leg_t *
 conflux_get_leg(conflux_t *cfx, const circuit_t *circ)
 {
   conflux_leg_t *leg_found = NULL;
+  tor_assert(cfx);
+  tor_assert(cfx->legs);
 
   // Find the leg that the cell is written on
   CONFLUX_FOR_EACH_LEG_BEGIN(cfx, leg) {

src/core/or/conflux_params.c

@@ -56,6 +56,11 @@
 #define NUM_LEGS_SET_MAX (UINT8_MAX)
 #define NUM_LEGS_SET_DEFAULT (2)
 
+/* For "cfx_max_legs_set" */
+#define MAX_LEGS_SET_MIN (3)
+#define MAX_LEGS_SET_MAX (UINT8_MAX)
+#define MAX_LEGS_SET_DEFAULT (8)
+
 /* For "cfx_send_pct". */
 #define CFX_SEND_PCT_MIN (0)
 #define CFX_SEND_PCT_MAX (255)
@@ -81,6 +86,8 @@ static uint8_t max_prebuilt_set = MAX_PREBUILT_SET_DEFAULT;
 STATIC uint32_t max_unlinked_leg_retry = MAX_UNLINKED_LEG_RETRY_DEFAULT;
 /* Number of legs per set. */
 static uint8_t num_legs_set = NUM_LEGS_SET_DEFAULT;
+/* Maximum number of legs per set allowed at exits */
+static uint8_t max_legs_set = MAX_LEGS_SET_DEFAULT;
 /* The low Exit relay threshold, as a ratio between 0 and 1, used as a limit to
  * decide the amount of pre-built set we build depending on how many Exit relay
  * supports conflux in our current consensus. */
@@ -223,6 +230,13 @@ conflux_params_get_num_legs_set(void)
   return num_legs_set;
 }
 
+/** Return the maximum number of legs per set. */
+uint8_t
+conflux_params_get_max_legs_set(void)
+{
+  return max_legs_set;
+}
+
 /** Return the drain percent we must hit before switching */
 uint8_t
 conflux_params_get_drain_pct(void)
@@ -275,6 +289,11 @@ conflux_params_new_consensus(const networkstatus_t *ns)
                             NUM_LEGS_SET_DEFAULT,
                             NUM_LEGS_SET_MIN, NUM_LEGS_SET_MAX);
 
+  max_legs_set =
+    networkstatus_get_param(ns, "cfx_max_legs_set",
+                            MAX_LEGS_SET_DEFAULT,
+                            MAX_LEGS_SET_MIN, MAX_LEGS_SET_MAX);
+
   /* Params used by conflux.c */
   cfx_send_pct = networkstatus_get_param(ns, "cfx_send_pct",
       CFX_SEND_PCT_DFLT,

src/core/or/conflux_params.h

@@ -16,6 +16,7 @@ uint8_t conflux_params_get_max_linked_set(void);
 uint8_t conflux_params_get_max_prebuilt(void);
 uint8_t conflux_params_get_max_unlinked_leg_retry(void);
 uint8_t conflux_params_get_num_legs_set(void);
+uint8_t conflux_params_get_max_legs_set(void);
 uint8_t conflux_params_get_drain_pct(void);
 uint8_t conflux_params_get_send_pct(void);
 

src/core/or/conflux_pool.c

@@ -187,6 +187,8 @@ conflux_free_(conflux_t *cfx)
   if (!cfx) {
     return;
   }
+  tor_assert(cfx->legs);
+  tor_assert(cfx->ooo_q);
 
   SMARTLIST_FOREACH_BEGIN(cfx->legs, conflux_leg_t *, leg) {
     SMARTLIST_DEL_CURRENT(cfx->legs, leg);
@@ -260,6 +262,8 @@ unlinked_free(unlinked_circuits_t *unlinked)
   if (!unlinked) {
     return;
   }
+  tor_assert(unlinked->legs);
+
   /* This cfx is pointing to a linked set. */
   if (!unlinked->is_for_linked_set) {
     conflux_free(unlinked->cfx);
@@ -493,10 +497,6 @@ cfx_add_leg(conflux_t *cfx, leg_t *leg)
   /* Big trouble if we add a leg to the wrong set. */
   tor_assert(tor_memeq(cfx->nonce, leg->link->nonce, sizeof(cfx->nonce)));
 
-  if (BUG(CONFLUX_NUM_LEGS(cfx) > CONFLUX_MAX_CIRCS)) {
-    return;
-  }
-
   conflux_leg_t *cleg = tor_malloc_zero(sizeof(*cleg));
   cleg->circ = leg->circ;
   // TODO-329-ARTI: Blindly copying the values from the cell. Is this correct?
@@ -731,6 +731,9 @@ try_finalize_set(unlinked_circuits_t *unlinked)
   bool is_client;
 
   tor_assert(unlinked);
+  tor_assert(unlinked->legs);
+  tor_assert(unlinked->cfx);
+  tor_assert(unlinked->cfx->legs);
 
   /* Without legs, this is not ready to become a linked set. */
   if (BUG(smartlist_len(unlinked->legs) == 0)) {
@@ -738,6 +741,17 @@ try_finalize_set(unlinked_circuits_t *unlinked)
     goto end;
   }
 
+  /* If there are too many legs, we can't link. */
+  if (smartlist_len(unlinked->legs) +
+      smartlist_len(unlinked->cfx->legs) > conflux_params_get_max_legs_set()) {
+    log_fn(LOG_PROTOCOL_WARN, LD_CIRC,
+           "Conflux set has too many legs to link. "
+           "Rejecting this circuit.");
+    conflux_log_set(LOG_PROTOCOL_WARN, unlinked->cfx, unlinked->is_client);
+    err = ERR_LINK_CIRC_INVALID_LEG;
+    goto end;
+  }
+
   /* Validate that all legs are coherent and parameters match. On failure, we
    * teardown the whole unlinked set because this means we either have a code
    * flow problem or the Exit is trying to trick us. */
@@ -1601,6 +1615,9 @@ linked_circuit_free(circuit_t *circ, bool is_client)
 {
   tor_assert(circ);
   tor_assert(circ->conflux);
+  tor_assert(circ->conflux->legs);
+  tor_assert(circ->conflux->ooo_q);
+
   if (is_client) {
     tor_assert(circ->purpose == CIRCUIT_PURPOSE_CONFLUX_LINKED);
   }

src/core/or/conflux_st.h

@@ -22,19 +22,6 @@ typedef enum {
  CONFLUX_ALG_CWNDRTT = 2,
 } conflux_alg_t;
 
-/**
- * Maximum number of linked circuits.
- *
- * We want to experiment with 3 guards, so we need at least 3 here.
- *
- * However, we need 1 more than this, to support using a test circuit to probe
- * for a faster path, for applications that *require* a specific latency target
- * (like VoIP).
- *
- * We may also want to raise this for traffic analysis defense evaluation.
- */
-#define CONFLUX_MAX_CIRCS 4
-
 /** XXX: Cached consensus params+scheduling alg */
 struct conflux_params_t {
   conflux_alg_t alg;