commit a02002dc9915d4f26d374f0784c7cbf916a653b0 Author: Nick Mathewson <nickm@torproject.org> Date: Tue Aug 11 17:01:49 2020 -0400 Lower the minimum value for MaxMemInQueues to 64 MB for relays. For clients, there is no minimum value; in both cases, we warn if the value seems too low. Closes ticket 24308. --- changes/ticket24308 | 6 ++++++ src/app/config/config.c | 25 +++++++++++++++++++++---- 2 files changed, 27 insertions(+), 4 deletions(-) diff --git a/changes/ticket24308 b/changes/ticket24308 new file mode 100644 index 0000000000..e614785265 --- /dev/null +++ b/changes/ticket24308 @@ -0,0 +1,6 @@ + o Minor features (denial-of-service memory limiter): + - Allow the user to configure even lower values for the MaxMemInQueues + parameter. Relays now enforce a minimum of 64 MB, when previously + the minimum was 256 MB. On clients, there is no minimum. Relays and + clients will both warn if the value is set so low that Tor is likely + to stop working. Closes ticket 24308. diff --git a/src/app/config/config.c b/src/app/config/config.c index 8e21d67f23..94971e3bfd 100644 --- a/src/app/config/config.c +++ b/src/app/config/config.c @@ -4585,6 +4585,9 @@ options_validate(or_options_t *old_options, or_options_t *options, STATIC uint64_t compute_real_max_mem_in_queues(const uint64_t val, bool is_server) { +#define MIN_SERVER_MB 64 +#define MIN_UNWARNED_SERVER_MB 256 +#define MIN_UNWARNED_CLIENT_MB 64 uint64_t result; if (val == 0) { @@ -4650,10 +4653,24 @@ compute_real_max_mem_in_queues(const uint64_t val, bool is_server) notice_sent = 1; } return result; - } else if (val < ONE_GIGABYTE / 4) { - log_warn(LD_CONFIG, "MaxMemInQueues must be at least 256 MB for now. " - "Ideally, have it as large as you can afford."); - return ONE_GIGABYTE / 4; + } else if (is_server && val < ONE_MEGABYTE * MIN_SERVER_MB) { + /* We can't configure less than this much on a server. */ + log_warn(LD_CONFIG, "MaxMemInQueues must be at least %d MB on servers " + "for now. Ideally, have it as large as you can afford.", + MIN_SERVER_MB); + return MIN_SERVER_MB * ONE_MEGABYTE; + } else if (is_server && val < ONE_MEGABYTE * MIN_UNWARNED_SERVER_MB) { + /* On a server, if it's less than this much, we warn that things + * may go badly. */ + log_warn(LD_CONFIG, "MaxMemInQueues is set to a low value; if your " + "relay doesn't work, this may be the reason why."); + return val; + } else if (! is_server && val < ONE_MEGABYTE * MIN_UNWARNED_CLIENT_MB) { + /* On a client, if it's less than this much, we warn that things + * may go badly. */ + log_warn(LD_CONFIG, "MaxMemInQueues is set to a low value; if your " + "client doesn't work, this may be the reason why."); + return val; } else { /* The value was fine all along */ return val;