DKIM: tighter checking while parsing signature headers. Bug 2217

diff --git a/doc/doc-txt/ChangeLog b/doc/doc-txt/ChangeLog
index 08ed2ce9d1b262a15b47e8f0d138a692c9f98881..14795e243de6841212aa77b07053271f500fed83 100644 (file)
--- a/doc/doc-txt/ChangeLog
+++ b/doc/doc-txt/ChangeLog
@@ -11,6 +11,12 @@ Since Exim version 4.90
 JH/03 Fix pgsql lookup for multiple result-tuples with a single column.
       Previously only the last row was returned.
 
+JH/04 Bug 2217: Tighten up the parsing of DKIM signature headers. Previously
+      we assumed that tags in the header were well-formed, and parsed the
+      element content after inspecting only the first char of the tag.
+      Assumptions at that stage could crash the receive process on malformed
+      input.
+
 
 Exim version 4.90
 -----------------

diff --git a/src/src/pdkim/pdkim.c b/src/src/pdkim/pdkim.c
index 20366a461fa1a5b152ad3441408f1003642ebeb9..b884671da9867888e04ffb6362e24a1543abad68 100644 (file)
--- a/src/src/pdkim/pdkim.c
+++ b/src/src/pdkim/pdkim.c
@@ -490,7 +490,12 @@ for (p = raw_hdr; ; p++)
 
     if (c == ';' || c == '\0')
       {
-      if (cur_tag && cur_val)
+      /* We must have both tag and value, and tags must be one char except
+      for the possibility of "bh". */
+
+      if (  cur_tag && cur_val
+        && (cur_tag->ptr == 1 || *cur_tag->s == 'b')
+        )
         {
        (void) string_from_gstring(cur_val);
        pdkim_strtrim(cur_val);
@@ -500,8 +505,14 @@ for (p = raw_hdr; ; p++)
        switch (*cur_tag->s)
          {
          case 'b':
-           pdkim_decode_base64(cur_val->s,
-                           cur_tag->s[1] == 'h' ? &sig->bodyhash : &sig->sighash);
+           switch (cur_tag->s[1])
+             {
+             case '\0': pdkim_decode_base64(cur_val->s, &sig->sighash); break;
+             case 'h':  if (cur_tag->ptr == 2)
+                          pdkim_decode_base64(cur_val->s, &sig->bodyhash);
+                        break;
+             default:   break;
+             }
            break;
          case 'v':
              /* We only support version 1, and that is currently the