client, csr: copy the renewed cert's subject and SAN into reenroll CSRs

[yosuke-wolfssl]

Problem

wolfcert_client_reenroll() built the /simplereenroll CSR from the caller's meta alone, so its Subject and SAN could differ from the certificate being renewed. RFC 7030 section 4.2.2 requires them to be identical. The CLI reenroll had the same flaw and required --subject. A conformant EST server rejects such a renewal; a lax one issues a renamed certificate. No privilege boundary is crossed (the caller already holds the current key), so this is a conformance fix.

Fix (src/csr.c)

A new internal wolfcert_csr_build_ex() takes the certificate being renewed. The public wolfcert_csr_build() passes none, so enrollment output is unchanged. For a renewal it:

• rejects a meta that sets subject_dn or any san_* (WOLFCERT_ERR_BAD_ARG);
• copies the certificate's raw Subject and SAN, with its criticality, after the customize callback, so the identity is byte-identical; an empty Subject stays empty;
• refuses a Subject containing a 0x00 byte (e.g. BMPString), or a Subject or SAN too large for the wolfSSL Cert (WOLFCERT_ERR_UNSUPPORTED);
• reads past an unrecognised critical extension, since it only reads the identity and does not validate the certificate.

The CSR buffer is now sized for the Subject and SAN it carries, which also lifts the old limit on large SANs at enrollment.

Caller	Before	After
wolfcert_client_reenroll() with meta.subject_dn / san_*	used in the CSR	WOLFCERT_ERR_BAD_ARG
wolfcert-client reenroll --subject / --san-*	--subject required	rejected

wolfcert-client reenroll now goes through wolfcert_client_reenroll() and prints the error detail. The link probes add GetASNTag / GetLength, which are exported under the same condition as the helpers already required. client.h lists the renewal error codes; types.h and ARCHITECTURE.md describe the copy; EMBEDDED.md adds the renewal Subject limit and corrects its Cert sizing figures (~23 CertName fields, ~5 KB for the trimmed example).

Closes f-12109.

Tests

• test_csr: empty Subject with critical and non-critical SAN, kept against a customize callback that sets a CN; a reverse-order multi-RDN certificate with an unknown critical extension (raw Subject compared byte for byte); extensions without a SAN; BMPString Subject refused; 60-name SAN; SAN added by customize dropped; key PEM passed as the certificate; each identity field in meta rejected.
• test_est_tls_roundtrip: meta rejection, renaming customize callback, rekey.
• cli_proto_scoping: --subject and each --san-* rejected on reenroll.

Verification

• 30/30 with CMake and autoconf; EST off 16/16, SCEP off 24/24; -Werror clean.
• ASan+UBSan with leak detection clean (CI cmake-full-asan-ubsan, Linux).
• Zephyr qemu_x86: wolfcert.unit.csr passes in 6-20 s against its 180 s limit.
• Each new test fails when the behaviour it guards is reverted.

Not in this PR

• A successful CLI reenroll test, which needs a CLI test driven against a running server.

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[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #44

Scan targets checked: wolfcert-src, wolfcert-bugs
Coverage: 1 of 5 in-scope changed file(s) opened by the reviewer; not opened: tests/integration/test_est_tls_roundtrip.c, tests/unit/test_csr.c, wolfcert/client.h, wolfcert/types.h

Fenrir result: Approved ✅

No new issues found in the changed files.

Advisory only — this automated result does not count as a GitHub approval.

Review tier: Lite