Server: support Linux abstract sockets for unixsocket via the @ prefix - #15575
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Crossref: #15572 |
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The server's Unix-socket bind (anetUnixServer) copies the path with redis_strlcpy and binds with sizeof(sockaddr_un), so the abstract namespace -- whose addresses begin with a NUL byte -- has never been reachable. This maps a leading '@' to the abstract namespace, following the convention established by socat and systemd, on Linux only. One shared helper (anetUnixAddr) builds the address for both anetUnixServer and anetUnixGenericConnect, so the "is this socket already in use" probe in connUnixListen keeps working for abstract names too. The subtle half is the address length: for pathname sockets trailing padding is ignored, but for abstract sockets every byte up to the given length is part of the name, so the address must be bound and dialed with EXACTLY offsetof(sun_path) + 1 + strlen(name). Lifecycle differences handled where they arise rather than special-cased later: - no chmod: abstract sockets have no filesystem presence, so unixsocketperm cannot apply (anetListen skips it when sun_path[0] is NUL); - no unlink, before bind (connUnixListen) or at shutdown (server.c): there is no file, and the name vanishes with the listener. redis.conf documents the form. Client-side support for the same convention (redis-cli/redis-benchmark via hiredis) is the sibling branch marc/uds-abstract-sockets; the two compose but do not depend on each other.
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@mgravell, what about handling https://github.com/redis/redis/pull/15572/changes together in this PR? otherwise the daily will fail after this PR is merged. |
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Support Linux abstract sockets for unixsocket via the @ prefix
This is the server half of #15577
Note tests are dependent on the client half, #15572
The server's Unix-socket bind (anetUnixServer) copies the path with redis_strlcpy and binds with sizeof(sockaddr_un), so the abstract namespace -- whose addresses begin with a NUL byte -- has never been reachable. This maps a leading '@' to the abstract namespace, following the convention established by socat and systemd, on Linux only.
One shared helper (anetUnixAddr) builds the address for both anetUnixServer and anetUnixGenericConnect, so the "is this socket already in use" probe in connUnixListen keeps working for abstract names too. The subtle half is the address length: for pathname sockets trailing padding is ignored, but for abstract sockets every byte up to the given length is part of the name, so the address must be bound and dialed with EXACTLY offsetof(sun_path) + 1 + strlen(name).
Lifecycle differences handled where they arise rather than special-cased later:
redis.conf documents the form. Client-side support for the same convention (redis-cli/redis-benchmark via hiredis) is the sibling branch marc/uds-abstract-sockets; the two compose but do not depend on each other.
Note
Medium Risk
Changes low-level Unix socket bind/connect behavior and listen/shutdown lifecycle; abstract sockets weaken filesystem-based access control compared to pathname sockets with
unixsocketperm.Overview
Adds Linux abstract Unix domain sockets for
unixsocketwhen the configured name starts with@(socat/systemd convention), so listeners need no filesystem socket file or cleanup.anetUnixAddrcentralizes sockaddr construction and exactsocklen_tfor bind/connect (critical for abstract names, where padding would change the socket identity). Connect/bind now enforce name length limits that pathname sockets previously lacked on the connect path.Lifecycle:
unixsocketperm/chmodare skipped for abstract sockets;unlinkis not run before bind (unix.c) or on shutdown (server.c).redis.confdocuments behavior and security (no file permissions—rely on ACLs/network namespace). Linux integration tests cover PING, no filesystem entry, and collision detection.Reviewed by Cursor Bugbot for commit 4a46b37. Bugbot is set up for automated code reviews on this repo. Configure here.