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init: make inbound tx relay percentage configurable
Public commit record
85/100 · Strong
What the developer wrote
Authored by Amiti Uttarwar
init: make inbound tx relay percentage configurable
Permit users to change the amount of inbounds that are permitted to relay
transactions. This is particularly relevant to ensure that superusers that are
not concerned with resource usage are not artificially restricted from offering
many transaction relay slots to the network.
Co-authored-by: Martin Zumsande <mzumsande@gmail.com>
✓ Specific, descriptive subject✓ Names a concrete action or component✓ Provides detailed explanatory context✓ Explains rationale or failure mode
What changed, and why it matters
This commit adds a new user-configurable setting called -inboundrelaypercent to Bitcoin Core. It lets node operators choose what percentage of incoming peer connections are allowed to relay transactions, instead of being hard-coded to 50%. The change itself is a feature/configuration tweak, not a fix for an active security bug. It could indirectly affect resource usage or network behavior if set unwisely, but it does not introduce a clear vulnerability.
Recommended action
No immediate security action required. Reviewers may want to confirm that edge cases (e.g., very low -maxconnections combined with high -inboundrelaypercent) behave sensibly and that the clamping prevents negative or >100 values as intended.
Security signals we found
01
New configuration option affecting P2P connection slot allocation
02
Input clamped to 0-100 via std::clamp, preventing out-of-range values
03
No validation, cryptography, or consensus code modified
04
No privilege escalation, remote code execution, or denial-of-service primitive introduced by the diff
Evidence from the diff
The patch makes the previously hard-coded FULL_RELAY_INBOUND_PCT (50%) into a configurable option, -inboundrelaypercent, with a default of 50% and clamped range 0-100. The value is passed through CConnman::Options to CConnman initialization and used to compute m_max_inbound_full_relay. Functional tests are updated to exercise 0% and 100% values and to replace a large -maxconnections=150 workaround with -inboundrelaypercent=100. No memory-safety, authentication, or consensus changes are present.
Changed components
src/init.cpp argument parsing and node initializationsrc/net.h CConnman::Options and inbound full-relay slot calculationtest/functional/p2p_connection_limits.pytest/functional/p2p_opportunistic_1p1c.pyInspect captured patch +19 / −6
diff --git a/src/init.cpp b/src/init.cpp
index 7f708412..c9363ba9 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -578,11 +578,12 @@ void SetupServerArgs(ArgsManager& argsman, bool can_listen_ipc)
argsman.AddArg("-forcednsseed", strprintf("Always query for peer addresses via DNS lookup (default: %u)", DEFAULT_FORCEDNSSEED), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
argsman.AddArg("-listen", strprintf("Accept connections from outside (default: %u if no -proxy, -connect or -maxconnections=0)", DEFAULT_LISTEN), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
argsman.AddArg("-listenonion", strprintf("Automatically create Tor onion service (default: %d)", DEFAULT_LISTEN_ONION), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
- argsman.AddArg("-maxconnections=<n>", strprintf("Maintain at most <n> automatic connections to peers (default: %u). %u slots of these are reserved for outgoing connections, %u percent of the remaining ones can support transaction relay. "
+ argsman.AddArg("-maxconnections=<n>", strprintf("Maintain at most <n> automatic connections to peers (default: %u). %u slots of these are reserved for outgoing connections. See -inboundrelaypercent for more information about limits applied to transaction relay inbound peers. "
"This limit does not apply to connections manually added via -addnode or the addnode RPC, which have a separate limit of %u. "
"It does not apply to short-lived private broadcast connections either, which have a separate limit of %u.",
- DEFAULT_MAX_PEER_CONNECTIONS, MAX_OUTBOUND_FULL_RELAY_CONNECTIONS + MAX_BLOCK_RELAY_ONLY_CONNECTIONS + MAX_FEELER_CONNECTIONS, static_cast<int>(100 * FULL_RELAY_INBOUND_PCT), MAX_ADDNODE_CONNECTIONS, MAX_PRIVATE_BROADCAST_CONNECTIONS),
+ DEFAULT_MAX_PEER_CONNECTIONS, MAX_OUTBOUND_FULL_RELAY_CONNECTIONS + MAX_BLOCK_RELAY_ONLY_CONNECTIONS + MAX_FEELER_CONNECTIONS, MAX_ADDNODE_CONNECTIONS, MAX_PRIVATE_BROADCAST_CONNECTIONS),
ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
+ argsman.AddArg("-inboundrelaypercent=<n>", strprintf("Permit a maximum percent of inbound connections to relay transactions, to limit memory utilization (0 to 100, default: %u).", DEFAULT_FULL_RELAY_INBOUND_PCT), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
argsman.AddArg("-maxreceivebuffer=<n>", strprintf("Maximum per-connection receive buffer, <n>*1000 bytes (default: %u)", DEFAULT_MAXRECEIVEBUFFER), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
argsman.AddArg("-maxsendbuffer=<n>", strprintf("Maximum per-connection memory usage for the send buffer, <n>*1000 bytes (default: %u)", DEFAULT_MAXSENDBUFFER), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
argsman.AddArg("-maxuploadtarget=<n>", strprintf("Tries to keep outbound traffic under the given target per 24h. Limit does not apply to peers with 'download' permission or blocks created within past week. 0 = no limit (default: %s). Optional suffix units [k|K|m|M|g|G|t|T] (default: M). Lowercase is 1000 base while uppercase is 1024 base", DEFAULT_MAX_UPLOAD_TARGET), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
@@ -2121,6 +2122,7 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
CConnman::Options connOptions;
connOptions.m_local_services = g_local_services;
connOptions.m_max_automatic_connections = nMaxConnections;
+ connOptions.m_full_relay_inbound_percent = std::clamp<int>(args.GetIntArg("-inboundrelaypercent", DEFAULT_FULL_RELAY_INBOUND_PCT), 0, 100);
connOptions.uiInterface = &uiInterface;
connOptions.m_banman = node.banman.get();
connOptions.m_msgproc = node.peerman.get();
diff --git a/src/net.h b/src/net.h
index fa5768cb..f1814120 100644
--- a/src/net.h
+++ b/src/net.h
@@ -79,8 +79,8 @@ static constexpr size_t MAX_PRIVATE_BROADCAST_CONNECTIONS{64};
static const bool DEFAULT_LISTEN = true;
/** The maximum number of peer connections to maintain. */
static const unsigned int DEFAULT_MAX_PEER_CONNECTIONS{200};
-/** Percentage of inbound connection slots that tx-relaying peers can use */
-static const int FULL_RELAY_INBOUND_PCT{50};
+/** Default percentage of inbound connection slots that tx-relaying peers can use */
+static const int DEFAULT_FULL_RELAY_INBOUND_PCT{50};
/** The default for -maxuploadtarget. 0 = Unlimited */
static const std::string DEFAULT_MAX_UPLOAD_TARGET{"0M"};
/** Default for blocks only*/
@@ -1089,6 +1089,7 @@ public:
{
ServiceFlags m_local_services = NODE_NONE;
int m_max_automatic_connections = DEFAULT_MAX_PEER_CONNECTIONS;
+ int m_full_relay_inbound_percent = DEFAULT_FULL_RELAY_INBOUND_PCT;
CClientUIInterface* uiInterface = nullptr;
NetEventsInterface* m_msgproc = nullptr;
BanMan* m_banman = nullptr;
@@ -1124,7 +1125,7 @@ public:
m_max_outbound_block_relay = std::min(MAX_BLOCK_RELAY_ONLY_CONNECTIONS, m_max_automatic_connections - m_max_outbound_full_relay);
m_max_automatic_outbound = m_max_outbound_full_relay + m_max_outbound_block_relay + m_max_feeler;
m_max_inbound = std::max(0, m_max_automatic_connections - m_max_automatic_outbound);
- m_max_inbound_full_relay = std::max(0, static_cast<int>(FULL_RELAY_INBOUND_PCT / 100.0 * m_max_inbound));
+ m_max_inbound_full_relay = std::max(0, static_cast<int>(connOptions.m_full_relay_inbound_percent / 100.0 * m_max_inbound));
m_use_addrman_outgoing = connOptions.m_use_addrman_outgoing;
m_client_interface = connOptions.uiInterface;
m_banman = connOptions.m_banman;
diff --git a/test/functional/p2p_connection_limits.py b/test/functional/p2p_connection_limits.py
index 20e34cab..338f8f74 100755
--- a/test/functional/p2p_connection_limits.py
+++ b/test/functional/p2p_connection_limits.py
@@ -58,6 +58,16 @@ class P2PConnectionLimits(BitcoinTestFramework):
self.nodes[0].add_p2p_connection(P2PInterface(), send_version=False, wait_for_verack=False, expect_success=False)
self.wait_until(lambda: len(node.getpeerinfo()) == 2)
+ self.log.info('Test different values of inboundrelaypercent')
+ self.restart_node(0, ['-maxconnections=13', '-inboundrelaypercent=0'])
+ with node.assert_debug_log(['failed to find a tx-relaying eviction candidate - connection dropped'], timeout=2):
+ self.nodes[0].add_p2p_connection(P2PInterface(), expect_success=False, wait_for_verack=False)
+
+ self.restart_node(0, ['-maxconnections=13', '-inboundrelaypercent=100'])
+ node.add_p2p_connection(P2PInterface())
+ node.add_p2p_connection(P2PInterface())
+ self.wait_until(lambda: len(node.getpeerinfo()) == 2)
+
if __name__ == '__main__':
P2PConnectionLimits(__file__).main()
diff --git a/test/functional/p2p_opportunistic_1p1c.py b/test/functional/p2p_opportunistic_1p1c.py
index 6841d7c3..156ffd9a 100755
--- a/test/functional/p2p_opportunistic_1p1c.py
+++ b/test/functional/p2p_opportunistic_1p1c.py
@@ -76,7 +76,7 @@ class PackageRelayTest(BitcoinTestFramework):
self.setup_clean_chain = True
self.num_nodes = 1
self.extra_args = [[
- "-maxmempool=5","-maxconnections=150"
+ "-maxmempool=5","-inboundrelaypercent=100"
]]
def create_tx_below_mempoolminfee(self, wallet, utxo_to_spend=None):
Risk score
Our methodology →Why this scored 20/100
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