QUICServerCredentials{selfSigned} shelled out to the openssl CLI and kept
the pair in the fixed /tmp/crafter-network-quic-cert/, guarded by an
in-process mutex only. Three things went wrong with that:
- Processes started at once (crafter-build runs tests in parallel, and
inside the Flatpak they share one /tmp) each found no pair and each
ran `openssl req` over the same key.pem and cert.pem, which it writes
in place one after the other. A process could load one run's key with
another's certificate and fail in ConfigurationLoadCredential.
- /tmp is shared by every user of the machine: whoever made the
directory first could keep everyone else from writing there, or plant
a pair in it.
- Without the openssl CLI there was no certificate at all, and
ComputeCertificateHashSHA256 piped the file through it as well.
The pair now lives in $XDG_CACHE_HOME/crafter-network/quic-cert/ (else
~/.cache/..., else $XDG_RUNTIME_DIR/...). Missing directories are made
0700, and the last is opened O_NOFOLLOW, refused unless the user owns
it, and made 0700 if it was not. A POSIX record lock on a file in it,
given up on after 10 s, covers both the check of the pair on disk and
its replacement, so one process makes the pair and the rest read it;
each file is written under a temporary name, fsynced and renamed into
place; and the listener hands msquic the pair from memory as PKCS#12
(QUIC_CREDENTIAL_TYPE_CERTIFICATE_PKCS12) instead of the two paths, so
a replacement cannot land between its reads of the key and the
certificate. A pair that does not parse, whose key does not match, or
that has less than a day left is replaced, which also repairs one a
crash tore between the two renames. A record lock rather than flock: an
flock is shared with a child forked while another thread holds it, and
the child holds it for its whole life. Threads of one process are kept
apart by the existing mutex, and the process keeps the pair it loaded,
so all its listeners serve one certificate until it nears its end.
The certificate is made in-process by :TLS in the shape the CLI
produced (ECDSA P-256, ecdsa-with-SHA256, 10 days, BasicConstraints
CA:FALSE, KeyUsage digitalSignature, EKU serverAuth, SANs localhost,
127.0.0.1 and ::1), with a random serial where the CLI also drew one;
ComputeCertificateHashSHA256 is X509_digest over the file's
certificate. The OpenSSL helpers are module-internal declarations in
:TLS, so libssl stays behind that one partition, and the TLS
partition's own development certificate is unchanged.
As before, the pair is reused across restarts while valid, so a
browser's pinned hash survives one; it is now replaced a day before it
expires rather than after, so a server is not started on a certificate
about to lapse. In the Flatpak, where /tmp went away with the last
instance, it now survives between runs too.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Jorijn van der Graaf
61d3e8c26a