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 26be5d85d0..96f21eea33 100644 --- a/src/app/config/config.c +++ b/src/app/config/config.c @@ -4050,8 +4050,11 @@ options_validate_cb(const void *old_options_, void *options_, char **msg) * actual maximum value. We clip this value if it's too low, and autodetect * it if it's set to 0. */ STATIC uint64_t -compute_real_max_mem_in_queues(const uint64_t val, int log_guess) +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) { @@ -4109,7 +4112,7 @@ compute_real_max_mem_in_queues(const uint64_t val, int log_guess) result = avail; } } - if (log_guess && ! notice_sent) { + if (is_server && ! notice_sent) { log_notice(LD_CONFIG, "%sMaxMemInQueues is set to %"PRIu64" MB. " "You can override this by setting MaxMemInQueues by hand.", ram ? "Based on detected system memory, " : "", @@ -4117,10 +4120,24 @@ compute_real_max_mem_in_queues(const uint64_t val, int log_guess) 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; diff --git a/src/app/config/config.h b/src/app/config/config.h index ee39490072..e95ef4a728 100644 --- a/src/app/config/config.h +++ b/src/app/config/config.h @@ -291,7 +291,7 @@ STATIC int parse_dir_authority_line(const char *line, STATIC int parse_dir_fallback_line(const char *line, int validate_only); STATIC uint64_t compute_real_max_mem_in_queues(const uint64_t val, - int log_guess); + bool is_server); STATIC int open_and_add_file_log(const log_severity_list_t *severity, const char *fname, int truncate_log);