/************************************************* * Exim - an Internet mail transport agent * *************************************************/ /* Copyright (c) University of Cambridge, 1995 - 2017 */ /* See the file NOTICE for conditions of use and distribution. */ /* Code for DKIM support. Other DKIM relevant code is in receive.c, transport.c and transports/smtp.c */ #include "exim.h" #ifndef DISABLE_DKIM #include "pdkim/pdkim.h" int dkim_verify_oldpool; pdkim_ctx *dkim_verify_ctx = NULL; pdkim_signature *dkim_signatures = NULL; pdkim_signature *dkim_cur_sig = NULL; static const uschar * dkim_collect_error = NULL; /*XXX the caller only uses the first record if we return multiple. Could we hand back an allocated string? */ static int dkim_exim_query_dns_txt(char *name, char *answer) { dns_answer dnsa; dns_scan dnss; dns_record *rr; lookup_dnssec_authenticated = NULL; if (dns_lookup(&dnsa, US name, T_TXT, NULL) != DNS_SUCCEED) return PDKIM_FAIL; /*XXX better error detail? logging? */ /* Search for TXT record */ for (rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS); rr; rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT)) if (rr->type == T_TXT) { int rr_offset = 0; int answer_offset = 0; /* Copy record content to the answer buffer */ while (rr_offset < rr->size) { uschar len = rr->data[rr_offset++]; snprintf(answer + answer_offset, PDKIM_DNS_TXT_MAX_RECLEN - answer_offset, "%.*s", (int)len, CS (rr->data + rr_offset)); rr_offset += len; answer_offset += len; if (answer_offset >= PDKIM_DNS_TXT_MAX_RECLEN) return PDKIM_FAIL; /*XXX better error detail? logging? */ } return PDKIM_OK; } return PDKIM_FAIL; /*XXX better error detail? logging? */ } void dkim_exim_init(void) { pdkim_init(); } void dkim_exim_verify_init(BOOL dot_stuffing) { /* There is a store-reset between header & body reception so cannot use the main pool. Any allocs done by Exim memory-handling must use the perm pool. */ dkim_verify_oldpool = store_pool; store_pool = POOL_PERM; /* Free previous context if there is one */ if (dkim_verify_ctx) pdkim_free_ctx(dkim_verify_ctx); /* Create new context */ dkim_verify_ctx = pdkim_init_verify(&dkim_exim_query_dns_txt, dot_stuffing); dkim_collect_input = !!dkim_verify_ctx; dkim_collect_error = NULL; /* Start feed up with any cached data */ receive_get_cache(); store_pool = dkim_verify_oldpool; } void dkim_exim_verify_feed(uschar * data, int len) { int rc; store_pool = POOL_PERM; if ( dkim_collect_input && (rc = pdkim_feed(dkim_verify_ctx, data, len)) != PDKIM_OK) { dkim_collect_error = pdkim_errstr(rc); log_write(0, LOG_MAIN, "DKIM: validation error: %.100s", dkim_collect_error); dkim_collect_input = FALSE; } store_pool = dkim_verify_oldpool; } void dkim_exim_verify_finish(void) { pdkim_signature * sig = NULL; int dkim_signers_size = 0, dkim_signers_ptr = 0, rc; const uschar * errstr; store_pool = POOL_PERM; /* Delete eventual previous signature chain */ dkim_signers = NULL; dkim_signatures = NULL; if (dkim_collect_error) { log_write(0, LOG_MAIN, "DKIM: Error during validation, disabling signature verification: %.100s", dkim_collect_error); dkim_disable_verify = TRUE; goto out; } dkim_collect_input = FALSE; /* Finish DKIM operation and fetch link to signatures chain */ rc = pdkim_feed_finish(dkim_verify_ctx, &dkim_signatures, &errstr); if (rc != PDKIM_OK) { log_write(0, LOG_MAIN, "DKIM: validation error: %.100s%s%s", pdkim_errstr(rc), errstr ? ": " : "", errstr ? errstr : US""); goto out; } for (sig = dkim_signatures; sig; sig = sig->next) { int size = 0, ptr = 0; uschar * logmsg = NULL, * s; /* Log a line for each signature */ if (!(s = sig->domain)) s = US""; logmsg = string_append(logmsg, &size, &ptr, 2, "d=", s); if (!(s = sig->selector)) s = US""; logmsg = string_append(logmsg, &size, &ptr, 2, " s=", s); logmsg = string_append(logmsg, &size, &ptr, 7, " c=", sig->canon_headers == PDKIM_CANON_SIMPLE ? "simple" : "relaxed", "/", sig->canon_body == PDKIM_CANON_SIMPLE ? "simple" : "relaxed", " a=", dkim_sig_to_a_tag(sig), string_sprintf(" b=%d", (int)sig->sighash.len > -1 ? sig->sighash.len * 8 : 0)); if ((s= sig->identity)) logmsg = string_append(logmsg, &size, &ptr, 2, " i=", s); if (sig->created > 0) logmsg = string_append(logmsg, &size, &ptr, 1, string_sprintf(" t=%lu", sig->created)); if (sig->expires > 0) logmsg = string_append(logmsg, &size, &ptr, 1, string_sprintf(" x=%lu", sig->expires)); if (sig->bodylength > -1) logmsg = string_append(logmsg, &size, &ptr, 1, string_sprintf(" l=%lu", sig->bodylength)); switch (sig->verify_status) { case PDKIM_VERIFY_NONE: logmsg = string_append(logmsg, &size, &ptr, 1, " [not verified]"); break; case PDKIM_VERIFY_INVALID: logmsg = string_append(logmsg, &size, &ptr, 1, " [invalid - "); switch (sig->verify_ext_status) { case PDKIM_VERIFY_INVALID_PUBKEY_UNAVAILABLE: logmsg = string_append(logmsg, &size, &ptr, 1, "public key record (currently?) unavailable]"); break; case PDKIM_VERIFY_INVALID_BUFFER_SIZE: logmsg = string_append(logmsg, &size, &ptr, 1, "overlong public key record]"); break; case PDKIM_VERIFY_INVALID_PUBKEY_DNSRECORD: case PDKIM_VERIFY_INVALID_PUBKEY_IMPORT: logmsg = string_append(logmsg, &size, &ptr, 1, "syntax error in public key record]"); break; case PDKIM_VERIFY_INVALID_SIGNATURE_ERROR: logmsg = string_append(logmsg, &size, &ptr, 1, "signature tag missing or invalid]"); break; case PDKIM_VERIFY_INVALID_DKIM_VERSION: logmsg = string_append(logmsg, &size, &ptr, 1, "unsupported DKIM version]"); break; default: logmsg = string_append(logmsg, &size, &ptr, 1, "unspecified problem]"); } break; case PDKIM_VERIFY_FAIL: logmsg = string_append(logmsg, &size, &ptr, 1, " [verification failed - "); switch (sig->verify_ext_status) { case PDKIM_VERIFY_FAIL_BODY: logmsg = string_append(logmsg, &size, &ptr, 1, "body hash mismatch (body probably modified in transit)]"); break; case PDKIM_VERIFY_FAIL_MESSAGE: logmsg = string_append(logmsg, &size, &ptr, 1, "signature did not verify (headers probably modified in transit)]"); break; default: logmsg = string_append(logmsg, &size, &ptr, 1, "unspecified reason]"); } break; case PDKIM_VERIFY_PASS: logmsg = string_append(logmsg, &size, &ptr, 1, " [verification succeeded]"); break; } logmsg[ptr] = '\0'; log_write(0, LOG_MAIN, "DKIM: %s", logmsg); /* Build a colon-separated list of signing domains (and identities, if present) in dkim_signers */ if (sig->domain) dkim_signers = string_append_listele(dkim_signers, &dkim_signers_size, &dkim_signers_ptr, ':', sig->domain); if (sig->identity) dkim_signers = string_append_listele(dkim_signers, &dkim_signers_size, &dkim_signers_ptr, ':', sig->identity); /* Process next signature */ } out: store_pool = dkim_verify_oldpool; } void dkim_exim_acl_setup(uschar * id) { pdkim_signature * sig; uschar * cmp_val; dkim_cur_sig = NULL; dkim_cur_signer = id; if (dkim_disable_verify || !id || !dkim_verify_ctx) return; /* Find signature to run ACL on */ for (sig = dkim_signatures; sig; sig = sig->next) if ( (cmp_val = Ustrchr(id, '@') != NULL ? US sig->identity : US sig->domain) && strcmpic(cmp_val, id) == 0 ) { dkim_cur_sig = sig; /* The "dkim_domain" and "dkim_selector" expansion variables have related globals, since they are used in the signing code too. Instead of inventing separate names for verification, we set them here. This is easy since a domain and selector is guaranteed to be in a signature. The other dkim_* expansion items are dynamically fetched from dkim_cur_sig at expansion time (see function below). */ dkim_signing_domain = US sig->domain; dkim_signing_selector = US sig->selector; dkim_key_length = sig->sighash.len * 8; return; } } static uschar * dkim_exim_expand_defaults(int what) { switch (what) { case DKIM_ALGO: return US""; case DKIM_BODYLENGTH: return US"9999999999999"; case DKIM_CANON_BODY: return US""; case DKIM_CANON_HEADERS: return US""; case DKIM_COPIEDHEADERS: return US""; case DKIM_CREATED: return US"0"; case DKIM_EXPIRES: return US"9999999999999"; case DKIM_HEADERNAMES: return US""; case DKIM_IDENTITY: return US""; case DKIM_KEY_GRANULARITY: return US"*"; case DKIM_KEY_SRVTYPE: return US"*"; case DKIM_KEY_NOTES: return US""; case DKIM_KEY_TESTING: return US"0"; case DKIM_NOSUBDOMAINS: return US"0"; case DKIM_VERIFY_STATUS: return US"none"; case DKIM_VERIFY_REASON: return US""; default: return US""; } } uschar * dkim_exim_expand_query(int what) { if (!dkim_verify_ctx || dkim_disable_verify || !dkim_cur_sig) return dkim_exim_expand_defaults(what); switch (what) { case DKIM_ALGO: return dkim_sig_to_a_tag(dkim_cur_sig); case DKIM_BODYLENGTH: return dkim_cur_sig->bodylength >= 0 ? string_sprintf(OFF_T_FMT, (LONGLONG_T) dkim_cur_sig->bodylength) : dkim_exim_expand_defaults(what); case DKIM_CANON_BODY: switch (dkim_cur_sig->canon_body) { case PDKIM_CANON_RELAXED: return US"relaxed"; case PDKIM_CANON_SIMPLE: default: return US"simple"; } case DKIM_CANON_HEADERS: switch (dkim_cur_sig->canon_headers) { case PDKIM_CANON_RELAXED: return US"relaxed"; case PDKIM_CANON_SIMPLE: default: return US"simple"; } case DKIM_COPIEDHEADERS: return dkim_cur_sig->copiedheaders ? US dkim_cur_sig->copiedheaders : dkim_exim_expand_defaults(what); case DKIM_CREATED: return dkim_cur_sig->created > 0 ? string_sprintf("%llu", dkim_cur_sig->created) : dkim_exim_expand_defaults(what); case DKIM_EXPIRES: return dkim_cur_sig->expires > 0 ? string_sprintf("%llu", dkim_cur_sig->expires) : dkim_exim_expand_defaults(what); case DKIM_HEADERNAMES: return dkim_cur_sig->headernames ? dkim_cur_sig->headernames : dkim_exim_expand_defaults(what); case DKIM_IDENTITY: return dkim_cur_sig->identity ? US dkim_cur_sig->identity : dkim_exim_expand_defaults(what); case DKIM_KEY_GRANULARITY: return dkim_cur_sig->pubkey ? dkim_cur_sig->pubkey->granularity ? US dkim_cur_sig->pubkey->granularity : dkim_exim_expand_defaults(what) : dkim_exim_expand_defaults(what); case DKIM_KEY_SRVTYPE: return dkim_cur_sig->pubkey ? dkim_cur_sig->pubkey->srvtype ? US dkim_cur_sig->pubkey->srvtype : dkim_exim_expand_defaults(what) : dkim_exim_expand_defaults(what); case DKIM_KEY_NOTES: return dkim_cur_sig->pubkey ? dkim_cur_sig->pubkey->notes ? US dkim_cur_sig->pubkey->notes : dkim_exim_expand_defaults(what) : dkim_exim_expand_defaults(what); case DKIM_KEY_TESTING: return dkim_cur_sig->pubkey ? dkim_cur_sig->pubkey->testing ? US"1" : dkim_exim_expand_defaults(what) : dkim_exim_expand_defaults(what); case DKIM_NOSUBDOMAINS: return dkim_cur_sig->pubkey ? dkim_cur_sig->pubkey->no_subdomaining ? US"1" : dkim_exim_expand_defaults(what) : dkim_exim_expand_defaults(what); case DKIM_VERIFY_STATUS: switch (dkim_cur_sig->verify_status) { case PDKIM_VERIFY_INVALID: return US"invalid"; case PDKIM_VERIFY_FAIL: return US"fail"; case PDKIM_VERIFY_PASS: return US"pass"; case PDKIM_VERIFY_NONE: default: return US"none"; } case DKIM_VERIFY_REASON: switch (dkim_cur_sig->verify_ext_status) { case PDKIM_VERIFY_INVALID_PUBKEY_UNAVAILABLE: return US"pubkey_unavailable"; case PDKIM_VERIFY_INVALID_PUBKEY_DNSRECORD:return US"pubkey_dns_syntax"; case PDKIM_VERIFY_INVALID_PUBKEY_IMPORT: return US"pubkey_der_syntax"; case PDKIM_VERIFY_FAIL_BODY: return US"bodyhash_mismatch"; case PDKIM_VERIFY_FAIL_MESSAGE: return US"signature_incorrect"; } default: return US""; } } /* Generate signatures for the given file, returning a string. If a prefix is given, prepend it to the file for the calculations. */ blob * dkim_exim_sign(int fd, off_t off, uschar * prefix, struct ob_dkim * dkim, const uschar ** errstr) { const uschar * dkim_domain; int sep = 0; uschar * seen_doms = NULL; int seen_doms_size = 0; int seen_doms_offset = 0; pdkim_ctx ctx; pdkim_signature * sig; blob * sigbuf = NULL; int sigsize = 0; int pdkim_rc; int sread; uschar buf[4096]; int save_errno = 0; int old_pool = store_pool; uschar * errwhen; store_pool = POOL_MAIN; pdkim_init_context(&ctx, dkim->dot_stuffed, &dkim_exim_query_dns_txt); if (!(dkim_domain = expand_cstring(dkim->dkim_domain))) /* expansion error, do not send message. */ { errwhen = US"dkim_domain"; goto expand_bad; } /* Set $dkim_domain expansion variable to each unique domain in list. */ while ((dkim_signing_domain = string_nextinlist(&dkim_domain, &sep, NULL, 0))) { const uschar * dkim_sel; int sel_sep = 0; if (dkim_signing_domain[0] == '\0') continue; /* Only sign once for each domain, no matter how often it appears in the expanded list. */ if (match_isinlist(dkim_signing_domain, CUSS &seen_doms, 0, NULL, NULL, MCL_STRING, TRUE, NULL) == OK) continue; seen_doms = string_append_listele(seen_doms, &seen_doms_size, &seen_doms_offset, ':', dkim_signing_domain); /* Set $dkim_selector expansion variable to each selector in list, for this domain. */ if (!(dkim_sel = expand_string(dkim->dkim_selector))) if (!(dkim_signing_selector = expand_string(dkim->dkim_selector))) { errwhen = US"dkim_selector"; goto expand_bad; } while ((dkim_signing_selector = string_nextinlist(&dkim_sel, &sel_sep, NULL, 0))) { uschar * dkim_canon_expanded; int pdkim_canon; uschar * dkim_sign_headers_expanded = NULL; uschar * dkim_private_key_expanded; uschar * dkim_hash_expanded; uschar * dkim_identity_expanded = NULL; /* Get canonicalization to use */ dkim_canon_expanded = dkim->dkim_canon ? expand_string(dkim->dkim_canon) : US"relaxed"; if (!dkim_canon_expanded) /* expansion error, do not send message. */ { errwhen = US"dkim_canon"; goto expand_bad; } if (Ustrcmp(dkim_canon_expanded, "relaxed") == 0) pdkim_canon = PDKIM_CANON_RELAXED; else if (Ustrcmp(dkim_canon_expanded, "simple") == 0) pdkim_canon = PDKIM_CANON_SIMPLE; else { log_write(0, LOG_MAIN, "DKIM: unknown canonicalization method '%s', defaulting to 'relaxed'.\n", dkim_canon_expanded); pdkim_canon = PDKIM_CANON_RELAXED; } if ( dkim->dkim_sign_headers && !(dkim_sign_headers_expanded = expand_string(dkim->dkim_sign_headers))) { errwhen = US"dkim_sign_header"; goto expand_bad; } /* else pass NULL, which means default header list */ /* Get private key to use. */ if (!(dkim_private_key_expanded = expand_string(dkim->dkim_private_key))) { errwhen = US"dkim_private_key"; goto expand_bad; } if ( Ustrlen(dkim_private_key_expanded) == 0 || Ustrcmp(dkim_private_key_expanded, "0") == 0 || Ustrcmp(dkim_private_key_expanded, "false") == 0 ) continue; /* don't sign, but no error */ if (dkim_private_key_expanded[0] == '/') { int privkey_fd, off = 0, len; /* Looks like a filename, load the private key. */ memset(big_buffer, 0, big_buffer_size); if ((privkey_fd = open(CS dkim_private_key_expanded, O_RDONLY)) < 0) { log_write(0, LOG_MAIN | LOG_PANIC, "unable to open " "private key file for reading: %s", dkim_private_key_expanded); goto bad; } do { if ((len = read(privkey_fd, big_buffer + off, big_buffer_size - 2 - off)) < 0) { (void) close(privkey_fd); log_write(0, LOG_MAIN|LOG_PANIC, "unable to read private key file: %s", dkim_private_key_expanded); goto bad; } off += len; } while (len > 0); (void) close(privkey_fd); big_buffer[off] = '\0'; dkim_private_key_expanded = big_buffer; } if (!(dkim_hash_expanded = expand_string(dkim->dkim_hash))) { errwhen = US"dkim_hash"; goto expand_bad; } if (dkim->dkim_identity) if (!(dkim_identity_expanded = expand_string(dkim->dkim_identity))) { errwhen = US"dkim_identity"; goto expand_bad; } else if (!*dkim_identity_expanded) dkim_identity_expanded = NULL; /*XXX so we currently nail signing to RSA + this hash. Need to extract algo from privkey and check for disallowed combos. */ if (!(sig = pdkim_init_sign(&ctx, dkim_signing_domain, dkim_signing_selector, dkim_private_key_expanded, dkim_hash_expanded, errstr ))) goto bad; dkim_private_key_expanded[0] = '\0'; pdkim_set_optional(sig, CS dkim_sign_headers_expanded, dkim_identity_expanded, pdkim_canon, pdkim_canon, -1, 0, 0); if (!ctx.sig) /* link sig to context chain */ ctx.sig = sig; else { pdkim_signature * n = ctx.sig; while (n->next) n = n->next; n->next = sig; } } } if (prefix) pdkim_feed(&ctx, prefix, Ustrlen(prefix)); if (lseek(fd, off, SEEK_SET) < 0) sread = -1; else while ((sread = read(fd, &buf, sizeof(buf))) > 0) if ((pdkim_rc = pdkim_feed(&ctx, buf, sread)) != PDKIM_OK) goto pk_bad; /* Handle failed read above. */ if (sread == -1) { debug_printf("DKIM: Error reading -K file.\n"); save_errno = errno; goto bad; } /* Build string of headers, one per signature */ if ((pdkim_rc = pdkim_feed_finish(&ctx, &sig, errstr)) != PDKIM_OK) goto pk_bad; sigbuf = store_get(sizeof(blob)); sigbuf->data = NULL; sigbuf->len = 0; while (sig) { int len = sigbuf->len; sigbuf->data = string_append(sigbuf->data, &sigsize, &len, 2, US sig->signature_header, US"\r\n"); sigbuf->len = len; sig = sig->next; } if (sigbuf->data) sigbuf->data[sigbuf->len] = '\0'; else sigbuf->data = US""; CLEANUP: store_pool = old_pool; errno = save_errno; return sigbuf; pk_bad: log_write(0, LOG_MAIN|LOG_PANIC, "DKIM: signing failed: %.100s", pdkim_errstr(pdkim_rc)); bad: sigbuf = NULL; goto CLEANUP; expand_bad: log_write(0, LOG_MAIN | LOG_PANIC, "failed to expand %s: %s", errwhen, expand_string_message); goto bad; } #endif