/* Provenance: openssl/openssl tls13_process_compressed_certificate (fixed).
 * repo: openssl/openssl
 * commit: 84f73f79af9f69c1527a9a372b7a9e771a394c2a
 * parent: b21663c35a6f0ed4c8de06855bdc7a6a21f00c2f
 * commit_url: https://github.com/openssl/openssl/commit/84f73f79af9f69c1527a9a372b7a9e771a394c2a
 * cve: CVE-2025-66199
 * license: Apache-2.0
 * function: tls13_process_compressed_certificate
 * relpath: ssl/statem/statem_lib.c
 */

MSG_PROCESS_RETURN tls13_process_compressed_certificate(SSL_CONNECTION *sc,
    PACKET *pkt,
    PACKET *tmppkt,
    BUF_MEM *buf)
{
    MSG_PROCESS_RETURN ret = MSG_PROCESS_ERROR;
    int comp_alg;
    COMP_METHOD *method = NULL;
    COMP_CTX *comp = NULL;
    size_t expected_length;
    size_t comp_length;
    int i;
    int found = 0;

    if (buf == NULL) {
        SSLfatal(sc, SSL_AD_INTERNAL_ERROR, ERR_R_INTERNAL_ERROR);
        goto err;
    }
    if (!PACKET_get_net_2(pkt, (unsigned int *)&comp_alg)) {
        SSLfatal(sc, SSL_AD_BAD_CERTIFICATE, ERR_R_INTERNAL_ERROR);
        goto err;
    }
    /* If we have a prefs list, make sure the algorithm is in it */
    if (sc->cert_comp_prefs[0] != TLSEXT_comp_cert_none) {
        for (i = 0; sc->cert_comp_prefs[i] != TLSEXT_comp_cert_none; i++) {
            if (sc->cert_comp_prefs[i] == comp_alg) {
                found = 1;
                break;
            }
        }
        if (!found) {
            SSLfatal(sc, SSL_AD_ILLEGAL_PARAMETER, SSL_R_BAD_COMPRESSION_ALGORITHM);
            goto err;
        }
    }
    if (!ossl_comp_has_alg(comp_alg)) {
        SSLfatal(sc, SSL_AD_BAD_CERTIFICATE, SSL_R_BAD_COMPRESSION_ALGORITHM);
        goto err;
    }
    switch (comp_alg) {
    case TLSEXT_comp_cert_zlib:
        method = COMP_zlib_oneshot();
        break;
    case TLSEXT_comp_cert_brotli:
        method = COMP_brotli_oneshot();
        break;
    case TLSEXT_comp_cert_zstd:
        method = COMP_zstd_oneshot();
        break;
    default:
        SSLfatal(sc, SSL_AD_BAD_CERTIFICATE, SSL_R_BAD_COMPRESSION_ALGORITHM);
        goto err;
    }

    if ((comp = COMP_CTX_new(method)) == NULL
        || !PACKET_get_net_3_len(pkt, &expected_length)
        || !PACKET_get_net_3_len(pkt, &comp_length)) {
        SSLfatal(sc, SSL_AD_BAD_CERTIFICATE, SSL_R_BAD_DECOMPRESSION);
        goto err;
    }

    /* Prevent excessive pre-decompression allocation */
    if (expected_length > sc->max_cert_list) {
        SSLfatal(sc, SSL_AD_BAD_CERTIFICATE, SSL_R_EXCESSIVE_MESSAGE_SIZE);
        goto err;
    }

    if (PACKET_remaining(pkt) != comp_length || comp_length == 0) {
        SSLfatal(sc, SSL_AD_DECODE_ERROR, SSL_R_BAD_DECOMPRESSION);
        goto err;
    }

    if (!BUF_MEM_grow(buf, expected_length)
        || !PACKET_buf_init(tmppkt, (unsigned char *)buf->data, expected_length)
        || COMP_expand_block(comp, (unsigned char *)buf->data, (int)expected_length,
               (unsigned char *)PACKET_data(pkt),
               (int)comp_length)
            != (int)expected_length) {
        SSLfatal(sc, SSL_AD_BAD_CERTIFICATE, SSL_R_BAD_DECOMPRESSION);
        goto err;
    }
    ret = MSG_PROCESS_CONTINUE_PROCESSING;
err:
    COMP_CTX_free(comp);
    return ret;
}