hs: Implement a helper to repurpose a circuit

When we repurpose a hidden service circuit, we need to clean up from the HS
circuit map and any HS related data structured contained in the circuit.

This commit adds an helper function that does it when repurposing a hidden
service circuit.

Fixes #29034

Signed-off-by: David Goulet <dgoulet@torproject.org>

6 files changed, 56 insertions, 0 deletions

diff --git a/changes/bug29034 b/changes/bug29034
new file mode 100644
index 0000000000..816b615009
--- /dev/null
+++ b/changes/bug29034
@@ -0,0 +1,5 @@
+  o Major bugfixes (Onion service reachability):
+    - Properly clean up the introduction point map and associated state when
+      circuits change purpose from onion service circuits to pathbias,
+      measurement, or other circuit types. This should fix some instances of
+      introduction point failure. Fixes bug 29034; bugfix on 0.3.2.1-alpha.
diff --git a/src/core/or/circuituse.c b/src/core/or/circuituse.c
index 02bfa15fb3..465d64215b 100644
--- a/src/core/or/circuituse.c
+++ b/src/core/or/circuituse.c
@@ -3052,6 +3052,12 @@ circuit_change_purpose(circuit_t *circ, uint8_t new_purpose)
 
   if (circ->purpose == new_purpose) return;
 
+  /* Take specific actions if we are repurposing a hidden service circuit. */
+  if (circuit_purpose_is_hidden_service(circ->purpose) &&
+      !circuit_purpose_is_hidden_service(new_purpose)) {
+    hs_circ_repurpose(circ);
+  }
+
   if (CIRCUIT_IS_ORIGIN(circ)) {
     char old_purpose_desc[80] = "";
 
diff --git a/src/feature/hs/hs_circuit.c b/src/feature/hs/hs_circuit.c
index e3873d2f18..2e59a357b3 100644
--- a/src/feature/hs/hs_circuit.c
+++ b/src/feature/hs/hs_circuit.c
@@ -24,6 +24,7 @@
 #include "feature/nodelist/describe.h"
 #include "feature/nodelist/nodelist.h"
 #include "feature/rend/rendservice.h"
+#include "feature/rend/rendcommon.h"
 #include "feature/stats/rephist.h"
 #include "lib/crypt_ops/crypto_dh.h"
 #include "lib/crypt_ops/crypto_rand.h"
@@ -1269,3 +1270,33 @@ hs_circ_cleanup(circuit_t *circ)
     hs_circuitmap_remove_circuit(circ);
   }
 }
+
+/* The given circuit will be repurposed so take the appropriate actions. A
+ * cleanup from the HS maps and of all HS related structures is done.
+ *
+ * Once this function returns, the circuit can be safely repurposed. */
+void
+hs_circ_repurpose(circuit_t *circ)
+{
+  origin_circuit_t *origin_circ;
+
+  tor_assert(circ);
+
+  /* Only repurposing an origin circuit is possible for HS. */
+  if (!CIRCUIT_IS_ORIGIN(circ)) {
+    return;
+  }
+  origin_circ = TO_ORIGIN_CIRCUIT(circ);
+
+  /* First, cleanup the circuit from the HS maps. */
+  hs_circ_cleanup(circ);
+
+  /* Depending on the version, different cleanup is done. */
+  if (origin_circ->rend_data) {
+    /* v2. */
+    rend_circ_cleanup(origin_circ);
+  } else if (origin_circ->hs_ident) {
+    /* v3. */
+    hs_ident_circuit_free(origin_circ->hs_ident);
+  }
+}
diff --git a/src/feature/hs/hs_circuit.h b/src/feature/hs/hs_circuit.h
index b8d8b25add..0786f3ee45 100644
--- a/src/feature/hs/hs_circuit.h
+++ b/src/feature/hs/hs_circuit.h
@@ -16,6 +16,7 @@
 
 /* Cleanup function when the circuit is closed or/and freed. */
 void hs_circ_cleanup(circuit_t *circ);
+void hs_circ_repurpose(circuit_t *circ);
 
 /* Circuit API. */
 int hs_circ_service_intro_has_opened(hs_service_t *service,
diff --git a/src/feature/rend/rendcommon.c b/src/feature/rend/rendcommon.c
index de48af795f..b10a5863b4 100644
--- a/src/feature/rend/rendcommon.c
+++ b/src/feature/rend/rendcommon.c
@@ -1045,3 +1045,14 @@ rend_circuit_pk_digest_eq(const origin_circuit_t *ocirc,
  match:
   return 1;
 }
+
+/* Cleanup the given circuit of all HS v2 data structure. */
+void
+rend_circ_cleanup(origin_circuit_t *circ)
+{
+  tor_assert(circ);
+
+  /* Both fields are set to NULL with these. */
+  crypto_pk_free(circ->intro_key);
+  rend_data_free(circ->rend_data);
+}
diff --git a/src/feature/rend/rendcommon.h b/src/feature/rend/rendcommon.h
index f136863c7a..c9a04846d7 100644
--- a/src/feature/rend/rendcommon.h
+++ b/src/feature/rend/rendcommon.h
@@ -71,6 +71,8 @@ int rend_non_anonymous_mode_enabled(const or_options_t *options);
 void assert_circ_anonymity_ok(const origin_circuit_t *circ,
                               const or_options_t *options);
 
+void rend_circ_cleanup(origin_circuit_t *circ);
+
 #ifdef RENDCOMMON_PRIVATE
 
 STATIC int