X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/fc2ba7b9fae5992dd76f721f283714a6d2ea137d..a85c067ba6c6940512cf57ec213277a370d87e70:/src/src/dkim.c

diff --git a/src/src/dkim.c b/src/src/dkim.c
index 8bb2efbf0..9b6e14a3f 100644
--- a/src/src/dkim.c
+++ b/src/src/dkim.c
@@ -2,8 +2,10 @@
 *     Exim - an Internet mail transport agent    *
 *************************************************/
 
+/* Copyright (c) The Exim Maintainers 2020 - 2022 */
 /* Copyright (c) University of Cambridge, 1995 - 2018 */
 /* See the file NOTICE for conditions of use and distribution. */
+/* SPDX-License-Identifier: GPL-2.0-only */
 
 /* Code for DKIM support. Other DKIM relevant code is in
    receive.c, transport.c and transports/smtp.c */
@@ -21,6 +23,7 @@ void
 params_dkim(void)
 {
 builtin_macro_create_var(US"_DKIM_SIGN_HEADERS", US PDKIM_DEFAULT_SIGN_HEADERS);
+builtin_macro_create_var(US"_DKIM_OVERSIGN_HEADERS", US PDKIM_OVERSIGN_HEADERS);
 }
 # else	/*!MACRO_PREDEF*/
 
@@ -37,36 +40,31 @@ static const uschar * dkim_collect_error = NULL;
 
 
 
-/*XXX the caller only uses the first record if we return multiple.
+/* Look up the DKIM record in DNS for the given hostname.
+Will use the first found if there are multiple.
+The return string is tainted, having come from off-site.
 */
 
 uschar *
 dkim_exim_query_dns_txt(const uschar * name)
 {
-/*XXX need to always alloc the dnsa, from tainted mem.
-Then, we hope, the answers will be tainted */
-
-dns_answer dnsa;
+dns_answer * dnsa = store_get_dns_answer();
 dns_scan dnss;
 rmark reset_point = store_mark();
-gstring * g = NULL;
+gstring * g = string_get_tainted(256, GET_TAINTED);
 
 lookup_dnssec_authenticated = NULL;
-if (dns_lookup(&dnsa, name, T_TXT, NULL) != DNS_SUCCEED)
-  return NULL;	/*XXX better error detail?  logging? */
+if (dns_lookup(dnsa, name, T_TXT, NULL) != DNS_SUCCEED)
+  goto bad;
 
 /* Search for TXT record */
 
-for (dns_record * rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS);
+for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
      rr;
-     rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT))
+     rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
   if (rr->type == T_TXT)
-    {
-    int rr_offset = 0;
-
-    /* Copy record content to the answer buffer */
-
-    while (rr_offset < rr->size)
+    {			/* Copy record content to the answer buffer */
+    for (int rr_offset = 0; rr_offset < rr->size; )
       {
       uschar len = rr->data[rr_offset++];
 
@@ -77,18 +75,20 @@ for (dns_record * rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS);
       rr_offset += len;
       }
 
-    /* check if this looks like a DKIM record */
+    /* Check if this looks like a DKIM record */
     if (Ustrncmp(g->s, "v=", 2) != 0 || strncasecmp(CS g->s, "v=dkim", 6) == 0)
       {
+      store_free_dns_answer(dnsa);
       gstring_release_unused(g);
       return string_from_gstring(g);
       }
 
-    if (g) g->ptr = 0;		/* overwrite previous record */
+    g->ptr = 0;		/* overwrite previous record */
     }
 
 bad:
 store_reset(reset_point);
+store_free_dns_answer(dnsa);
 return NULL;	/*XXX better error detail?  logging? */
 }
 
@@ -96,6 +96,8 @@ return NULL;	/*XXX better error detail?  logging? */
 void
 dkim_exim_init(void)
 {
+if (f.dkim_init_done) return;
+f.dkim_init_done = TRUE;
 pdkim_init();
 }
 
@@ -104,12 +106,17 @@ 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_exim_init();
+
+/* There is a store-reset between header & body reception for the main pool
+(actually, after every header line) so cannot use that as we need the data we
+store per-header, during header processing, at the end of body reception
+for evaluating the signature.  Any allocs done for dkim verify
+memory-handling must use a different pool.  We use a separate one that we
+can reset per message. */
 
 dkim_verify_oldpool = store_pool;
-store_pool = POOL_PERM;
+store_pool = POOL_MESSAGE;
 
 /* Free previous context if there is one */
 
@@ -122,19 +129,22 @@ dkim_verify_ctx = pdkim_init_verify(&dkim_exim_query_dns_txt, dot_stuffing);
 dkim_collect_input = dkim_verify_ctx ? DKIM_MAX_SIGNATURES : 0;
 dkim_collect_error = NULL;
 
-/* Start feed up with any cached data */
-receive_get_cache();
+/* Start feed up with any cached data, but limited to message data */
+receive_get_cache(chunking_state == CHUNKING_LAST
+		  ? chunking_data_left : GETC_BUFFER_UNLIMITED);
 
 store_pool = dkim_verify_oldpool;
 }
 
 
+/* Submit a chunk of data for verification input.
+Only use the data when the feed is activated. */
 void
 dkim_exim_verify_feed(uschar * data, int len)
 {
 int rc;
 
-store_pool = POOL_PERM;
+store_pool = POOL_MESSAGE;
 if (  dkim_collect_input
    && (rc = pdkim_feed(dkim_verify_ctx, data, len)) != PDKIM_OK)
   {
@@ -264,6 +274,11 @@ else
 		"(headers probably modified in transit)]");
 	  break;
 
+	case PDKIM_VERIFY_INVALID_PUBKEY_KEYSIZE:
+	  logmsg = string_cat(logmsg,
+		US"signature invalid (key too short)]");
+	  break;
+
 	default:
 	  logmsg = string_cat(logmsg, US"unspecified reason]");
 	}
@@ -295,7 +310,7 @@ int rc;
 gstring * g = NULL;
 const uschar * errstr = NULL;
 
-store_pool = POOL_PERM;
+store_pool = POOL_MESSAGE;
 
 /* Delete eventual previous signature chain */
 
@@ -402,7 +417,7 @@ for (pdkim_signature * sig = dkim_signatures; sig; sig = sig->next)
     dkim_cur_sig = sig;
     dkim_signing_domain = US sig->domain;
     dkim_signing_selector = US sig->selector;
-    dkim_key_length = sig->sighash.len * 8;
+    dkim_key_length = sig->keybits;
 
     /* These two return static strings, so we can compare the addr
     later to see if the ACL overwrote them.  Check that when logging */
@@ -556,6 +571,7 @@ switch (what)
 						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_INVALID_PUBKEY_KEYSIZE:	return US"pubkey_too_short";
       case PDKIM_VERIFY_FAIL_BODY:		return US"bodyhash_mismatch";
       case PDKIM_VERIFY_FAIL_MESSAGE:		return US"signature_incorrect";
       }
@@ -570,6 +586,8 @@ void
 dkim_exim_sign_init(void)
 {
 int old_pool = store_pool;
+
+dkim_exim_init();
 store_pool = POOL_MAIN;
 pdkim_init_context(&dkim_sign_ctx, FALSE, &dkim_exim_query_dns_txt);
 store_pool = old_pool;
@@ -848,6 +866,9 @@ for (pdkim_signature * sig = dkim_signatures; sig; sig = sig->next)
           g = string_cat(g,
 	    US"fail (signature did not verify; headers probably modified in transit)\n\t\t");
 	  break;
+        case PDKIM_VERIFY_INVALID_PUBKEY_KEYSIZE:	/* should this really be "polcy"? */
+          g = string_fmt_append(g, "fail (public key too short: %u bits)\n\t\t", sig->keybits);
+          break;
         default:
           g = string_cat(g, US"fail (unspecified reason)\n\t\t");
 	  break;