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-rw-r--r--src/tls/tls_fprint.c413
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diff --git a/src/tls/tls_fprint.c b/src/tls/tls_fprint.c
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+/*++
+/* NAME
+/* tls_fprint 3
+/* SUMMARY
+/* Digests fingerprints and all that.
+/* SYNOPSIS
+/* #include <tls.h>
+/*
+/* EVP_MD *tls_digest_byname(const char *mdalg, EVP_MD_CTX **mdctxPtr)
+/* const char *mdalg;
+/* EVP_MD_CTX **mdctxPtr;
+/*
+/* char *tls_serverid_digest(props, protomask, ciphers)
+/* const TLS_CLIENT_START_PROPS *props;
+/* long protomask;
+/* const char *ciphers;
+/*
+/* char *tls_digest_encode(md_buf, md_len)
+/* const unsigned char *md_buf;
+/* const char *md_len;
+/*
+/* char *tls_data_fprint(buf, len, mdalg)
+/* const char *buf;
+/* int len;
+/* const char *mdalg;
+/*
+/* char *tls_cert_fprint(peercert, mdalg)
+/* X509 *peercert;
+/* const char *mdalg;
+/*
+/* char *tls_pkey_fprint(peercert, mdalg)
+/* X509 *peercert;
+/* const char *mdalg;
+/* DESCRIPTION
+/* tls_digest_byname() constructs, and optionally returns, an EVP_MD_CTX
+/* handle for performing digest operations with the algorithm named by the
+/* mdalg parameter. The return value is non-null on success, and holds a
+/* digest algorithm handle. If the mdctxPtr argument is non-null the
+/* created context is returned to the caller, who is then responsible for
+/* deleting it by calling EVP_MD_ctx_free() once it is no longer needed.
+/*
+/* tls_digest_encode() converts a binary message digest to a hex ASCII
+/* format with ':' separators between each pair of hex digits.
+/* The return value is dynamically allocated with mymalloc(),
+/* and the caller must eventually free it with myfree().
+/*
+/* tls_data_fprint() digests unstructured data, and encodes the digested
+/* result via tls_digest_encode(). The return value is dynamically
+/* allocated with mymalloc(), and the caller must eventually free it
+/* with myfree().
+/*
+/* tls_cert_fprint() returns a fingerprint of the the given
+/* certificate using the requested message digest, formatted
+/* with tls_digest_encode(). Panics if the
+/* (previously verified) digest algorithm is not found. The return
+/* value is dynamically allocated with mymalloc(), and the caller
+/* must eventually free it with myfree().
+/*
+/* tls_pkey_fprint() returns a public-key fingerprint; in all
+/* other respects the function behaves as tls_cert_fprint().
+/* The var_tls_bc_pkey_fprint variable enables an incorrect
+/* algorithm that was used in Postfix versions 2.9.[0-5].
+/* The return value is dynamically allocated with mymalloc(),
+/* and the caller must eventually free it with myfree().
+/*
+/* tls_serverid_digest() suffixes props->serverid computed by the SMTP
+/* client with "&" plus a digest of additional parameters
+/* needed to ensure that re-used sessions are more likely to
+/* be reused and that they will satisfy all protocol and
+/* security requirements.
+/* The return value is dynamically allocated with mymalloc(),
+/* and the caller must eventually free it with myfree().
+/*
+/* Arguments:
+/* .IP mdalg
+/* A digest algorithm name, such as "sha256".
+/* .IP peercert
+/* Server or client X.509 certificate.
+/* .IP md_buf
+/* The raw binary digest.
+/* .IP md_len
+/* The digest length in bytes.
+/* .IP mdalg
+/* Name of a message digest algorithm suitable for computing secure
+/* (1st pre-image resistant) message digests of certificates. For now,
+/* md5, sha1, or member of SHA-2 family if supported by OpenSSL.
+/* .IP mdctxPtr
+/* Pointer to an (EVP_MD_CTX *) handle, or NULL if only probing for
+/* algorithm support without immediate use in mind.
+/* .IP buf
+/* Input data for the message digest algorithm mdalg.
+/* .IP len
+/* The length of the input data.
+/* .IP props
+/* The client start properties for the session, which contains the
+/* initial serverid from the SMTP client and the DANE verification
+/* parameters.
+/* .IP protomask
+/* The mask of protocol exclusions.
+/* .IP ciphers
+/* The SSL client cipherlist.
+/* LICENSE
+/* .ad
+/* .fi
+/* This software is free. You can do with it whatever you want.
+/* The original author kindly requests that you acknowledge
+/* the use of his software.
+/* AUTHOR(S)
+/* Wietse Venema
+/* IBM T.J. Watson Research
+/* P.O. Box 704
+/* Yorktown Heights, NY 10598, USA
+/*
+/* Viktor Dukhovni
+/*--*/
+
+/* System library. */
+
+#include <sys_defs.h>
+#include <ctype.h>
+
+#ifdef USE_TLS
+#include <string.h>
+
+/* Utility library. */
+
+#include <msg.h>
+#include <mymalloc.h>
+#include <stringops.h>
+
+/* Global library. */
+
+#include <mail_params.h>
+
+/* TLS library. */
+
+#define TLS_INTERNAL
+#include <tls.h>
+
+/* Application-specific. */
+
+static const char hexcodes[] = "0123456789ABCDEF";
+
+#define checkok(stillok) (ok = ok && (stillok))
+#define digest_data(p, l) checkok(EVP_DigestUpdate(mdctx, (char *)(p), (l)))
+#define digest_object(p) digest_data((p), sizeof(*(p)))
+#define digest_string(s) digest_data((s), strlen(s)+1)
+
+#define digest_dane(dane, memb) do { \
+ if ((dane)->memb != 0) \
+ checkok(digest_tlsa_usage(mdctx, (dane)->memb, #memb)); \
+ } while (0)
+
+#define digest_tlsa_argv(tlsa, memb) do { \
+ if ((tlsa)->memb) { \
+ digest_string(#memb); \
+ for (dgst = (tlsa)->memb->argv; *dgst; ++dgst) \
+ digest_string(*dgst); \
+ } \
+ } while (0)
+
+/* digest_tlsa_usage - digest TA or EE match list sorted by alg and value */
+
+static int digest_tlsa_usage(EVP_MD_CTX * mdctx, TLS_TLSA *tlsa,
+ const char *usage)
+{
+ char **dgst;
+ int ok = 1;
+
+ for (digest_string(usage); tlsa; tlsa = tlsa->next) {
+ digest_string(tlsa->mdalg);
+ digest_tlsa_argv(tlsa, pkeys);
+ digest_tlsa_argv(tlsa, certs);
+ }
+ return (ok);
+}
+
+/* tls_digest_byname - test availability or prepare to use digest */
+
+const EVP_MD *tls_digest_byname(const char *mdalg, EVP_MD_CTX **mdctxPtr)
+{
+ const EVP_MD *md;
+ EVP_MD_CTX *mdctx = NULL;
+ int ok = 1;
+
+ /*
+ * In OpenSSL 3.0, because of dynamically variable algorithm providers,
+ * there is a time-of-check/time-of-use issue that means that abstract
+ * algorithm handles returned by EVP_get_digestbyname() can (and not
+ * infrequently do) return ultimately unusable algorithms, to check for
+ * actual availability, one needs to use the new EVP_MD_fetch() API, or
+ * indirectly check usability by creating a concrete context. We take the
+ * latter approach here (works for 1.1.1 without #ifdef).
+ *
+ * Note that EVP_MD_CTX_{create,destroy} were renamed to, respectively,
+ * EVP_MD_CTX_{new,free} in OpenSSL 1.1.0.
+ */
+ checkok(md = EVP_get_digestbyname(mdalg));
+
+ /*
+ * Sanity check: Newer shared libraries could (hypothetical ABI break)
+ * allow larger digests, we avoid such poison algorithms.
+ */
+ checkok(EVP_MD_size(md) <= EVP_MAX_MD_SIZE);
+ checkok(mdctx = EVP_MD_CTX_new());
+ checkok(EVP_DigestInit_ex(mdctx, md, NULL));
+
+
+ if (ok && mdctxPtr != 0)
+ *mdctxPtr = mdctx;
+ else
+ EVP_MD_CTX_free(mdctx);
+ return (ok ? md : 0);
+}
+
+/* tls_serverid_digest - suffix props->serverid with parameter digest */
+
+char *tls_serverid_digest(const TLS_CLIENT_START_PROPS *props, long protomask,
+ const char *ciphers)
+{
+ EVP_MD_CTX *mdctx;
+ const char *mdalg;
+ unsigned char md_buf[EVP_MAX_MD_SIZE];
+ unsigned int md_len;
+ int ok = 1;
+ int i;
+ long sslversion;
+ VSTRING *result;
+
+ /*
+ * Try to use sha256: our serverid choice should be strong enough to
+ * resist 2nd-preimage attacks with a difficulty comparable to that of
+ * DANE TLSA digests. Failing that, we compute serverid digests with the
+ * default digest, but DANE requires sha256 and sha512, so if we must
+ * fall back to our default digest, DANE support won't be available. We
+ * panic if the fallback algorithm is not available, as it was verified
+ * available in tls_client_init() and must not simply vanish. Our
+ * provider set is not expected to change once the OpenSSL library is
+ * initialized.
+ */
+ if (tls_digest_byname(mdalg = LN_sha256, &mdctx) == 0
+ && tls_digest_byname(mdalg = props->mdalg, &mdctx) == 0)
+ msg_panic("digest algorithm \"%s\" not found", props->mdalg);
+
+ /* Salt the session lookup key with the OpenSSL runtime version. */
+ sslversion = OpenSSL_version_num();
+
+ digest_string(props->helo ? props->helo : "");
+ digest_object(&sslversion);
+ digest_object(&protomask);
+ digest_string(ciphers);
+
+ /*
+ * All we get from the session cache is a single bit telling us whether
+ * the certificate is trusted or not, but we need to know whether the
+ * trust is CA-based (in that case we must do name checks) or whether it
+ * is a direct end-point match. We mustn't confuse the two, so it is
+ * best to process only TA trust in the verify callback and check the EE
+ * trust after. This works since re-used sessions always have access to
+ * the leaf certificate, while only the original session has the leaf and
+ * the full trust chain.
+ *
+ * Only the trust anchor matchlist is hashed into the session key. The end
+ * entity certs are not used to determine whether a certificate is
+ * trusted or not, rather these are rechecked against the leaf cert
+ * outside the verification callback, each time a session is created or
+ * reused.
+ *
+ * Therefore, the security context of the session does not depend on the EE
+ * matching data, which is checked separately each time. So we exclude
+ * the EE part of the DANE structure from the serverid digest.
+ *
+ * If the security level is "dane", we send SNI information to the peer.
+ * This may cause it to respond with a non-default certificate. Since
+ * certificates for sessions with no or different SNI data may not match,
+ * we must include the SNI name in the session id.
+ */
+ if (props->dane) {
+ digest_dane(props->dane, ta);
+#if 0
+ digest_dane(props->dane, ee); /* See above */
+#endif
+ digest_string(TLS_DANE_BASED(props->tls_level) ? props->host : "");
+ }
+ checkok(EVP_DigestFinal_ex(mdctx, md_buf, &md_len));
+ EVP_MD_CTX_destroy(mdctx);
+ if (!ok)
+ msg_fatal("error computing %s message digest", mdalg);
+
+ /* Check for OpenSSL contract violation */
+ if (md_len > EVP_MAX_MD_SIZE)
+ msg_panic("unexpectedly large %s digest size: %u", mdalg, md_len);
+
+ /*
+ * Append the digest to the serverid. We don't compare this digest to
+ * any user-specified fingerprints. Therefore, we don't need to use a
+ * colon-separated format, which saves space in the TLS session cache and
+ * makes logging of session cache lookup keys more readable.
+ *
+ * This does however duplicate a few lines of code from the digest encoder
+ * for colon-separated cert and pkey fingerprints. If that is a
+ * compelling reason to consolidate, we could use that and append the
+ * result.
+ */
+ result = vstring_alloc(strlen(props->serverid) + 1 + 2 * md_len);
+ vstring_strcpy(result, props->serverid);
+ VSTRING_ADDCH(result, '&');
+ for (i = 0; i < md_len; i++) {
+ VSTRING_ADDCH(result, hexcodes[(md_buf[i] & 0xf0) >> 4U]);
+ VSTRING_ADDCH(result, hexcodes[(md_buf[i] & 0x0f)]);
+ }
+ VSTRING_TERMINATE(result);
+ return (vstring_export(result));
+}
+
+/* tls_digest_encode - encode message digest binary blob as xx:xx:... */
+
+char *tls_digest_encode(const unsigned char *md_buf, int md_len)
+{
+ int i;
+ char *result = mymalloc(md_len * 3);
+
+ /* Check for contract violation */
+ if (md_len > EVP_MAX_MD_SIZE || md_len >= INT_MAX / 3)
+ msg_panic("unexpectedly large message digest size: %u", md_len);
+
+ /* No risk of overrunes, len is bounded by OpenSSL digest length */
+ for (i = 0; i < md_len; i++) {
+ result[i * 3] = hexcodes[(md_buf[i] & 0xf0) >> 4U];
+ result[(i * 3) + 1] = hexcodes[(md_buf[i] & 0x0f)];
+ result[(i * 3) + 2] = (i + 1 != md_len) ? ':' : '\0';
+ }
+ return (result);
+}
+
+/* tls_data_fprint - compute and encode digest of binary object */
+
+char *tls_data_fprint(const char *buf, int len, const char *mdalg)
+{
+ EVP_MD_CTX *mdctx = NULL;
+ unsigned char md_buf[EVP_MAX_MD_SIZE];
+ unsigned int md_len;
+ int ok = 1;
+
+ /* Previously available in "init" routine. */
+ if (tls_digest_byname(mdalg, &mdctx) == 0)
+ msg_panic("digest algorithm \"%s\" not found", mdalg);
+
+ digest_data(buf, len);
+ checkok(EVP_DigestFinal_ex(mdctx, md_buf, &md_len));
+ EVP_MD_CTX_destroy(mdctx);
+ if (!ok)
+ msg_fatal("error computing %s message digest", mdalg);
+
+ return (tls_digest_encode(md_buf, md_len));
+}
+
+/* tls_cert_fprint - extract certificate fingerprint */
+
+char *tls_cert_fprint(X509 *peercert, const char *mdalg)
+{
+ int len;
+ char *buf;
+ char *buf2;
+ char *result;
+
+ len = i2d_X509(peercert, NULL);
+ buf2 = buf = mymalloc(len);
+ i2d_X509(peercert, (unsigned char **) &buf2);
+ if (buf2 - buf != len)
+ msg_panic("i2d_X509 invalid result length");
+
+ result = tls_data_fprint(buf, len, mdalg);
+ myfree(buf);
+
+ return (result);
+}
+
+/* tls_pkey_fprint - extract public key fingerprint from certificate */
+
+char *tls_pkey_fprint(X509 *peercert, const char *mdalg)
+{
+ if (var_tls_bc_pkey_fprint) {
+ const char *myname = "tls_pkey_fprint";
+ ASN1_BIT_STRING *key;
+ char *result;
+
+ key = X509_get0_pubkey_bitstr(peercert);
+ if (key == 0)
+ msg_fatal("%s: error extracting legacy public-key fingerprint: %m",
+ myname);
+
+ result = tls_data_fprint((char *) key->data, key->length, mdalg);
+ return (result);
+ } else {
+ int len;
+ char *buf;
+ char *buf2;
+ char *result;
+
+ len = i2d_X509_PUBKEY(X509_get_X509_PUBKEY(peercert), NULL);
+ buf2 = buf = mymalloc(len);
+ i2d_X509_PUBKEY(X509_get_X509_PUBKEY(peercert), (unsigned char **) &buf2);
+ if (buf2 - buf != len)
+ msg_panic("i2d_X509_PUBKEY invalid result length");
+
+ result = tls_data_fprint(buf, len, mdalg);
+ myfree(buf);
+ return (result);
+ }
+}
+
+#endif
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