security: fail closed on gRPC TLS errors, verify dialed server identity (#12263)

* security: fail closed on misconfigured gRPC TLS

LoadServerTLS/LoadClientTLS returned plaintext credentials on every
error path once TLS was configured: a typo in tls.min_version or
tls.cipher_suites, cert and key in different directories, or cert/key
set without grpc.ca all left the component serving or dialing
plaintext. A partially configured TLS setup now stops the process at
startup instead; leaving cert/key unset still means no TLS, as before.

The loaders also stat cert/key/ca files up front since the pemfile
providers read lazily and would otherwise only fail at handshake time.

Mirrored in the Rust volume server: partial grpc.volume cert/key, a
missing grpc.ca, or a rustls build failure now abort startup rather
than warn-and-continue on plaintext.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* security: optional server-identity allowlist for gRPC clients

The mTLS client accepts any certificate the configured CA signs, so a
per-workload CA lets one component stand in for any other: a filer
identity can answer as the master. The server side already screens
callers via allowed_commonNames and allowed_wildcard_domain; nothing
screened the server.

LoadClientTLS now wires AdditionalPeerVerification when the caller
configures a server allowlist: grpc.<component>.allowed_server_commonNames
(falling back to a shared grpc.allowed_server_commonNames) matched
against the peer cert's subject CN, DNS SANs, or URI SANs such as a
SPIFFE id, plus a grpc.allowed_server_wildcard_domain suffix match.
Leaving them unset keeps the previous behavior.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* security: URI SANs are exact-match only in the server identity allowlist

A URI identity whose path happens to end in the wildcard domain would
otherwise pass the DNS suffix check.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* security: tighten gRPC TLS fail-closed and server-identity paths

- URI SANs match the server-identity allowlist exactly; the wildcard
  domain suffix check applies only to CN and DNS SANs.
- A partially set client_cert/client_key pair is an error when the
  cert/key fallback is empty, instead of dialing plaintext.
- Cert/key/ca files are loaded and parsed at startup (LoadX509KeyPair
  and CA PEM validation) since pemfile providers read lazily.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* rust volume: error on a partial grpc client_cert/client_key pair

Mirror the Go loadClientTLS path: when client_cert or client_key is
set without its mate and the cert/key fallback is empty, fail instead
of dialing plaintext.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* security: wildcard domain match requires a valid hostname

A CA-signed identity like ".example.com" satisfied the bare suffix check
for wildcard ".example.com" despite not being a hostname. Require a real
subdomain: non-empty label before the suffix, a '.' boundary when the
configured wildcard has no leading dot, and DNS-name syntax. A leading
"*." label still matches so wildcard certs keep working. Applied to both
the Go server/client authenticators and the Rust volume's client-cert
verifier.

* security: ignore a trailing root dot in wildcard domain matching

* tls: reject a partial dedicated client cert/key pair instead of falling back

When exactly one of component.client_cert/client_key is set, warn-and-
fallback silently dialed with the serving identity. Fail closed like the
other TLS misconfigurations in this change; mirrored in the Rust loader.
Regression tests cover a partial pair with a valid fallback.

* rust volume: harden partial client cert pair test with real pem files

* security: verify dialed server identity per target kind on the filer

The filer reused one grpc.filer-verifying dial option for master, volume,
filer and s3 targets, so a broad allowlist accepted the wrong component at
the wrong port and a narrow one rejected legitimate peers. Outbound calls
now pick grpc.<target>.allowed_server_commonNames (falling back to the
client component's and the global list) while still presenting the
grpc.filer client identity.

* security: scope per-target server allowlists under the client component

The filer read grpc.volume.allowed_server_commonNames when dialing a
volume, but that key already denotes the volume's own outbound allowlist
(e.g. the master identity). A deployment restricting volume->master
calls would make the filer reject real volume servers. Per-target policy
now lives under the client component: grpc.filer.volume_*
falls back to grpc.filer.* then grpc.*.

---------

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

weed/command/scaffold/security.toml

@@ -83,10 +83,23 @@ expires_after_seconds = 10           # seconds
 # the component reuses cert/key for both directions.
 # If client and server certificates come from different issuing CAs, put both
 # CA certificates in the ca PEM file.
+# Once a component's cert/key are set, any error loading them or grpc.ca is
+# fatal: the component never falls back to plaintext.
 [grpc]
 ca = ""
 # Set wildcard domain for enable TLS authentication by common names
 allowed_wildcard_domain = "" # .mycompany.com
+# Optional allowlist a client checks the dialed server's certificate against:
+# the subject common name, a DNS SAN, or a URI SAN (e.g. a SPIFFE id) must be
+# listed, or match allowed_server_wildcard_domain, else the handshake fails.
+# With a per-workload CA, list the identities each server may present so one
+# workload cannot impersonate another component. Unset accepts any CA-signed
+# server certificate, as before. Any [grpc.<component>] section may set its own
+# allowed_server_commonNames to override this list, and scope it further per
+# dialed target, e.g. the filer reads [grpc.filer]
+# volume_allowed_server_commonNames for volume server calls.
+allowed_server_commonNames = ""      # comma-separated server identities
+allowed_server_wildcard_domain = ""  # .mycompany.com
 
 # Volume server gRPC options (server-side)
 # Enables mTLS for incoming gRPC connections to volume server