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commit 6fcae8e0d080d7d0875eab4a0118e8fdaf5e832c Author: David Goulet dgoulet@torproject.org AuthorDate: Tue Aug 2 15:49:03 2022 -0400

relay: Don't send DESTROY remote reason backward or forward

Fixes #40649

Signed-off-by: David Goulet dgoulet@torproject.org --- changes/ticket40649 | 4 ++++ src/core/or/command.c | 11 +++++++---- 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/changes/ticket40649 b/changes/ticket40649 new file mode 100644 index 0000000000..28df58f106 --- /dev/null +++ b/changes/ticket40649 @@ -0,0 +1,4 @@ + o Minor bugfixes (relay): + - Do not propagate either forward or backward a DESTROY remote reason when + closing a circuit so to avoid a possible side channel. Fixes bug 40649; + bugfix on 0.1.2.4-alpha. diff --git a/src/core/or/command.c b/src/core/or/command.c index 65853f7844..a8b93dc9a0 100644 --- a/src/core/or/command.c +++ b/src/core/or/command.c @@ -629,9 +629,11 @@ command_process_destroy_cell(cell_t *cell, channel_t *chan) if (!CIRCUIT_IS_ORIGIN(circ) && chan == TO_OR_CIRCUIT(circ)->p_chan && cell->circ_id == TO_OR_CIRCUIT(circ)->p_circ_id) { - /* the destroy came from behind */ + /* The destroy came from behind so nullify its p_chan. Close the circuit + * with a DESTROYED reason so we don't propagate along the path forward the + * reason which could be used as a side channel. */ circuit_set_p_circid_chan(TO_OR_CIRCUIT(circ), 0, NULL); - circuit_mark_for_close(circ, reason|END_CIRC_REASON_FLAG_REMOTE); + circuit_mark_for_close(circ, END_CIRC_REASON_DESTROYED); } else { /* the destroy came from ahead */ circuit_set_n_circid_chan(circ, 0, NULL); if (CIRCUIT_IS_ORIGIN(circ)) { @@ -639,9 +641,10 @@ command_process_destroy_cell(cell_t *cell, channel_t *chan) } else { /* Close the circuit so we stop queuing cells for it and propagate the * DESTROY cell down the circuit so relays can stop queuing in-flight - * cells for this circuit which helps with memory pressure. */ + * cells for this circuit which helps with memory pressure. We do NOT + * propagate the remote reason so not to create a side channel. */ log_debug(LD_OR, "Received DESTROY cell from n_chan, closing circuit."); - circuit_mark_for_close(circ, reason | END_CIRC_REASON_FLAG_REMOTE); + circuit_mark_for_close(circ, END_CIRC_REASON_DESTROYED); } } }