chan: Do not re-queue after a fail cell write

Couple things happen in this commit. First, we do not re-queue a cell back in
the circuit queue if the write packed cell failed. Currently, it is close to
impossible to have it failed but just in case, the channel is mark as closed
and we move on.

The second thing is that the channel_write_packed_cell() always took ownership
of the cell whatever the outcome. This means, on success or failure, it needs
to free it.

It turns out that that we were using the wrong free function in one case and
not freeing it in an other possible code path. So, this commit makes sure we
only free it in one place that is at the very end of
channel_write_packed_cell() which is the top layer of the channel abstraction.
This makes also channel_tls_write_packed_cell_method() return a negative value
on error.

Two unit tests had to be fixed (quite trivial) due to a double free of the
packed cell in the test since now we do free it in all cases correctly.

Part of #23709

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

1 files changed, 5 insertions, 6 deletions

diff --git a/src/or/channeltls.c b/src/or/channeltls.c
index e6ecc15381..023ccdefd3 100644
--- a/src/or/channeltls.c
+++ b/src/or/channeltls.c
@@ -832,6 +832,9 @@ channel_tls_write_cell_method(channel_t *chan, cell_t *cell)
  *
  * This implements the write_packed_cell method for channel_tls_t; given a
  * channel_tls_t and a packed_cell_t, transmit the packed_cell_t.
+ *
+ * Return 0 on success or negative value on error. The caller must free the
+ * packed cell.
  */
 
 static int
@@ -841,7 +844,6 @@ channel_tls_write_packed_cell_method(channel_t *chan,
   tor_assert(chan);
   channel_tls_t *tlschan = BASE_CHAN_TO_TLS(chan);
   size_t cell_network_size = get_cell_network_size(chan->wide_circ_ids);
-  int written = 0;
 
   tor_assert(tlschan);
   tor_assert(packed_cell);
@@ -849,18 +851,15 @@ channel_tls_write_packed_cell_method(channel_t *chan,
   if (tlschan->conn) {
     connection_buf_add(packed_cell->body, cell_network_size,
                             TO_CONN(tlschan->conn));
-
-    /* This is where the cell is finished; used to be done from relay.c */
-    packed_cell_free(packed_cell);
-    ++written;
   } else {
     log_info(LD_CHANNEL,
              "something called write_packed_cell on a tlschan "
              "(%p with ID " U64_FORMAT " but no conn",
              chan, U64_PRINTF_ARG(chan->global_identifier));
+    return -1;
   }
 
-  return written;
+  return 0;
 }
 
 /**