{ "number": 36305, "repo": "bitcoin/bitcoin", "url": "https://github.com/bitcoin/bitcoin/pull/36305", "title": "net: Use exclusive P2P listen sockets on Windows", "author": "winterrdog", "author_association": "CONTRIBUTOR", "created_at": "2026-09-20T22:11:54Z", "updated_at": "2026-10-27T18:54:38Z", "description_hash": "2ddb59ff671d1ff4", "age_days": 42, "draft": false, "labels": [ "Windows", "P2P" ], "milestone": null, "base": "master", "head_sha": "db31a3ad1f75538d07707d373adbfbe90ba8e328", "head_ref": "fix/p2p-exclusive-bind-win32", "head_repo": "winterrdog/bitcoin", "head_history": [ { "t": "2026-10-25T13:55:11Z", "sha": "36505a3992f509510250b9701b617a35594dbff3" }, { "t": "2026-10-27T15:42:41Z", "sha": "db31a3ad1f75538d07707d373adbfbe90ba8e328" } ], "additions": 31, "deletions": 0, "changed_files": 2, "commit_count": 2, "size_bucket": "S", "mergeable_state": "clean", "bot": { "drahtbot": { "present": true, "reviews": { "ack": [ { "login": "jpk68", "url": "https://github.com/bitcoin/bitcoin/pull/36305#issuecomment-6281543300" }, { "login": "hodlinator", "url": "https://github.com/bitcoin/bitcoin/pull/36305#pullrequestreview-5672657235" } ], "concept_ack": [ { "login": "hebasto", "url": "https://github.com/bitcoin/bitcoin/pull/36305#pullrequestreview-5652305051" } ] }, "conflicts": [] } }, "acks_parsed": { "jpk68": { "kind": "ack", "hash": "db31a3ad1f75538d07707d373adbfbe90ba8e328", "t": "2026-10-20T01:58:32Z", "stale": false }, "hodlinator": { "kind": "ack", "hash": "db31a3ad1f75538d07707d373adbfbe90ba8e328", "t": "2026-10-27T18:54:34Z", "stale": false }, "hebasto": { "kind": "concept_ack", "hash": null, "t": "2026-10-26T12:56:50Z", "stale": false } }, "acks_tally": { "ack": 2, "stale_ack": 0, "concept_ack": 1, "approach_ack": 0, "nack": 0, "concept_nack": 0, "approach_nack": 0 }, "reviews": { "approved": 2, "changes_requested": 0, "distinct_reviewers": [ "hebasto", "hodlinator", "jpk68" ] }, "signals": { "needs_rebase": false, "ci_failed": false, "mergeable_state": "clean", "last_author_activity": "2026-10-27T15:42:52Z", "last_reviewer_activity": "2026-10-27T18:54:34Z", "last_reviewer": "hodlinator", "author_silent_days": 5, "waiting_on_author_days": 5, "days_since_update": 5 }, "refs": { "mentioned": [ 36169 ], "depends_on": [], "fixes": [], "linked_issues": [], "references": [ { "number": 36169, "type": "pull", "state": "closed", "merged": true, "merged_at": "2026-09-06", "title": "http: Use SO_EXCLUSIVEADDRUSE on Windows" } ], "conflicts": [] }, "stack": { "shares_commits_with": [], "based_on": [], "base_for": [] }, "review_paths": [ "src/net.cpp", "test/functional/feature_port.py" ], "body": "on Windows, `SO_REUSEADDR` does not carry over the same semantics as on\nPOSIX systems. a second socket can set `SO_REUSEADDR` and bind to a\nport that is _already in use_ by another process running under\nthe _same_ user account. this means another local process could bind to\nthe P2P listen port and receive incoming connections intended for\n`bitcoind`.\n\nthis matters because the P2P listener is expected to have exclusive\nownership of its address and port. allowing another process to bind to\nit could let that process _intercept_ incoming P2P connections. this is\nin a similar spirit to #36169, which made the RPC listener exclusive on\nWindows.\n\nto fix this, we use `SO_EXCLUSIVEADDRUSE` for the P2P listen socket on\nWindows instead of `SO_REUSEADDR`, while retaining `SO_REUSEADDR` on\nother platforms. the added test verifies the expected behaviour by\nattempting to bind a second socket to the same port. on Windows, this\nfails with `WSAEACCES` (`10013`), which Python exposes as\n`PermissionError` (an `OSError` subclass).\n\nreferences:\n\n- https://learn.microsoft.com/en-us/windows/win32/winsock/using-so-reuseaddr-and-so-exclusiveaddruse\n- https://stackoverflow.com/questions/14388706/how-do-so-reuseaddr-and-so-reuseport-differ/14388707#14388707", "commits": [ { "sha": "0dbd271eb4a3263b8b81ccf22876429076bae574", "date": "2026-10-27T15:41:57Z", "message": "net: use exclusive P2P listen sockets on Windows\n\nOn Windows, `SO_REUSEADDR` does not give exclusive use of an address and\nport, so another process under the same user account can bind the same\nport and intercept incoming P2P connections.\n\nOn Windows, use `SO_EXCLUSIVEADDRUSE` instead. If the option cannot be\nset, fail the bind rather than listen on a port that could be hijacked." }, { "sha": "db31a3ad1f75538d07707d373adbfbe90ba8e328", "date": "2026-10-27T15:41:57Z", "message": "test: check P2P listen port exclusivity\n\nCheck both orderings of a port conflict: another socket cannot bind the\nP2P port while `bitcoind` is listening on it, and `bitcoind` refuses to\nstart if another socket already holds the port.\n\nCo-authored-by: hodlinator <172445034+hodlinator@users.noreply.github.com>" } ], "timeline": [ { "t": "2026-09-20T22:12:42Z", "kind": "comment", "who": "winterrdog", "assoc": "CONTRIBUTOR", "text": "indeed, this difference in `SO_REUSEADDR` behaviour across operating systems is\nsomewhat surprising, and has sparked similar discussions in Tornado,\nCPython, and Trio.\n\n- https://github.com/python-trio/trio/issues/39\n- https://github.com/tornadoweb/tornado/issues/550\n- https://github.com/python/cpython/issues/46802", "id": "c:5753047298", "url": "https://github.com/bitcoin/bitcoin/pull/36305#issuecomment-5753047298", "hash": "26207145d27d4530", "edited": "2026-09-25T07:19:09Z" }, { "t": "2026-10-20T01:58:32Z", "kind": "comment", "who": "jpk68", "assoc": "CONTRIBUTOR", "text": "ACK db31a3ad1f75538d07707d373adbfbe90ba8e328", "id": "c:6281543300", "url": "https://github.com/bitcoin/bitcoin/pull/36305#issuecomment-6281543300", "hash": "8f84354596867cf1", "edited": "2026-10-27T16:42:56Z" }, { "t": "2026-10-23T11:19:08Z", "kind": "review_comment", "who": "hodlinator", "assoc": "MEMBER", "path": "src/net.cpp", "commit": "c6971fd61036cf738606afa62826af47e4315730", "in_reply_to": null, "text": "Not sure why setting the option would fail, but I think we should treat it as a fatal error, same as in httpserver.cpp.\n```suggestion\n strError = Untranslated(strprintf(\"Error setting SO_EXCLUSIVEADDRUSE on socket: %s\", NetworkErrorString(WSAGetLastError())));\n LogError(\"%s\\n\", strError.original);\n return false;\n```\n\nhttps://learn.microsoft.com/en-us/windows/win32/winsock/using-so-reuseaddr-and-so-exclusiveaddruse state:\n[quoted text omitted]", "id": "rc:4358954387", "url": "https://github.com/bitcoin/bitcoin/pull/36305#discussion_r4358954387", "hash": "698117b17effb83d", "edited": "2026-10-23T11:24:33Z" }, { "t": "2026-10-23T11:22:09Z", "kind": "review_comment", "who": "hodlinator", "assoc": "MEMBER", "path": "test/functional/feature_port.py", "commit": "db31a3ad1f75538d07707d373adbfbe90ba8e328", "in_reply_to": null, "text": "Could also add a test for when the socket is bound before bitcoind:\n```diff\n--- a/test/functional/feature_port.py\n+++ b/test/functional/feature_port.py\n@@ -11,6 +11,7 @@ import socket\n from test_framework.test_framework import (\n BitcoinTestFramework,\n )\n+from test_framework.test_node import ErrorMatch\n from test_framework.util import (\n p2p_port,\n assert_raises,\n@@ -41,6 +42,17 @@ class PortTest(BitcoinTestFramework):\n # listener requested for exclusive address use.\n assert_raises(OSError, lambda: competing_listener.bind((\"0.0.0.0\", port1)))\n\n+ self.log.info(\"Verifying that we fail during startup if another process is bound to the port\")\n+ self.stop_node(0)\n+ with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as competing_listener:\n+ competing_listener.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)\n+ self.log.info(f\"Binding to {port1}, not {port2}\")\n+ competing_listener.bind((\"0.0.0.0\", port1))\n+ node.assert_start_raises_init_error(\n+ extra_args=[\"-listen\", f\"-port={port1}\"],\n+ expected_msg=fr\"^Error\\: Unable to bind to 0\\.0\\.0\\.0\\:{port1} on this computer\\..*\",\n+ match=ErrorMatch.PARTIAL_REGEX)\n+\n```\n(Edit: Realized the `setsockopt()` on the python side is probably not necessary).", "id": "rc:4358977350", "url": "https://github.com/bitcoin/bitcoin/pull/36305#discussion_r4358977350", "hash": "26a12c65614c3fca", "edited": "2026-10-23T11:39:55Z" }, { "t": "2026-10-23T11:24:33Z", "kind": "review", "who": "hodlinator", "assoc": "MEMBER", "state": "COMMENTED", "commit": "c6971fd61036cf738606afa62826af47e4315730", "text": "Concept ACK c6971fd61036cf738606afa62826af47e4315730", "id": "r:5627501696", "url": "https://github.com/bitcoin/bitcoin/pull/36305#pullrequestreview-5627501696", "hash": "3cdf366befe1d3ac", "edited": null }, { "t": "2026-10-25T13:55:11Z", "kind": "force_push", "who": "winterrdog", "commit": "36505a3992f509510250b9701b617a35594dbff3", "id": "push:36505a3992f509510250b9701b617a35594dbff3" }, { "t": "2026-10-25T13:56:00Z", "kind": "review_comment", "who": "winterrdog", "assoc": "CONTRIBUTOR", "path": "src/net.cpp", "commit": "c6971fd61036cf738606afa62826af47e4315730", "in_reply_to": 4358954387, "text": "correct, this is much better. fixed and thanks a lot!", "id": "rc:4371079797", "url": "https://github.com/bitcoin/bitcoin/pull/36305#discussion_r4371079797", "hash": "717471f848b64378", "edited": "2026-10-25T13:56:01Z" }, { "t": "2026-10-25T13:56:24Z", "kind": "review_comment", "who": "winterrdog", "assoc": "CONTRIBUTOR", "path": "test/functional/feature_port.py", "commit": "db31a3ad1f75538d07707d373adbfbe90ba8e328", "in_reply_to": 4358977350, "text": "i agreee, added the test\n\n[quoted text omitted]\nyes, we can leave out the Python-side `setsockopt()` because on Linux (and likely other POSIX systems), setting `SO_REUSEADDR` on both sockets would let `bitcoind` bind successfully (the Python socket is _only bound_ but does not listen), making the test fail. leaving it out is fine on Windows, since the first check (where `bitcoind` binds first) already catches that regression", "id": "rc:4371080995", "url": "https://github.com/bitcoin/bitcoin/pull/36305#discussion_r4371080995", "hash": "aeb7d13ec02d71eb", "edited": "2026-10-25T14:09:57Z" }, { "t": "2026-10-26T10:26:24Z", "kind": "review", "who": "hodlinator", "assoc": "MEMBER", "state": "APPROVED", "commit": "db31a3ad1f75538d07707d373adbfbe90ba8e328", "text": "ACK 36505a3992f509510250b9701b617a35594dbff3\n\nRan functional test on Windows. Thanks for taking my suggestions!", "id": "r:5650576646", "url": "https://github.com/bitcoin/bitcoin/pull/36305#pullrequestreview-5650576646", "hash": "1e1ff776a4a89712", "edited": "2026-10-27T15:42:41Z" }, { "t": "2026-10-26T12:56:50Z", "kind": "review", "who": "hebasto", "assoc": "MEMBER", "state": "COMMENTED", "commit": "36505a3992f509510250b9701b617a35594dbff3", "text": "Concept ACK.", "id": "r:5652305051", "url": "https://github.com/bitcoin/bitcoin/pull/36305#pullrequestreview-5652305051", "hash": "39bcd188b11b7a83", "edited": null }, { "t": "2026-10-27T13:31:02Z", "kind": "review", "who": "hebasto", "assoc": "MEMBER", "state": "COMMENTED", "commit": "36505a3992f509510250b9701b617a35594dbff3", "text": "I think the commits should be swapped. Otherwise, the first commit fails the test on Windows.", "id": "r:5667835205", "url": "https://github.com/bitcoin/bitcoin/pull/36305#pullrequestreview-5667835205", "hash": "41485d97df5022da", "edited": null }, { "t": "2026-10-27T15:42:41Z", "kind": "force_push", "who": "winterrdog", "commit": "db31a3ad1f75538d07707d373adbfbe90ba8e328", "id": "push:db31a3ad1f75538d07707d373adbfbe90ba8e328" }, { "t": "2026-10-27T15:42:52Z", "kind": "comment", "who": "winterrdog", "assoc": "CONTRIBUTOR", "text": "[quoted text omitted]\n\ndone", "id": "c:6446436450", "url": "https://github.com/bitcoin/bitcoin/pull/36305#issuecomment-6446436450", "hash": "8a1da63f179c110b", "edited": null }, { "t": "2026-10-27T18:54:34Z", "kind": "review", "who": "hodlinator", "assoc": "MEMBER", "state": "APPROVED", "commit": "db31a3ad1f75538d07707d373adbfbe90ba8e328", "text": "re-ACK db31a3ad1f75538d07707d373adbfbe90ba8e328\n\n[quoted text omitted]\nThink I've seen this recently in another PR, but just thought \"well, the ancestor commits CI doesn't run Windows anyway\", but I agree it's more correct to swap the order.", "id": "r:5672657235", "url": "https://github.com/bitcoin/bitcoin/pull/36305#pullrequestreview-5672657235", "hash": "45071201e0f7a5e7", "edited": null } ], "labels_log": [ { "t": "2026-09-20T22:11:57Z", "action": "labeled", "label": "P2P", "who": "DrahtBot" }, { "t": "2026-09-21T06:05:27Z", "action": "labeled", "label": "Windows", "who": "maflcko" } ], "state_log": [], "text_chars": 5204, "text_tokens_estimate": 1301, "changed_paths": [ "src/net.cpp", "test/functional/feature_port.py" ], "files": [ { "path": "src/net.cpp", "add": 12, "del": 0 }, { "path": "test/functional/feature_port.py", "add": 19, "del": 0 } ], "test_lines": 19, "git": { "head": "db31a3ad1f75538d07707d373adbfbe90ba8e328", "head_matches_backup": true, "base": "d48e76e689bb4d680d9d8a70b67f994be2f0cdd1", "patch_id": "17ee28726e3b24dc", "commits": [ { "sha": "0dbd271eb4", "subject": "net: use exclusive P2P listen sockets on Windows", "files": 1, "add": 12, "del": 0 }, { "sha": "db31a3ad1f", "subject": "test: check P2P listen port exclusivity", "files": 1, "add": 19, "del": 0 } ], "patch_truncated": false }, "patch_id": "17ee28726e3b24dc", "input_hash": "5311fd8bfe48b0b8", "extracted_at": "2026-11-02T01:09:49+00:00" }