bug#42029: `gnus-registry-spool-action' gets field beyond message headers

[tomotaka.suwa@gmail.com]

Hi,

I've been suffering from `mail-source-crash-box' on getting new mail.

After some debug and investigation, I noticed that
`mail-extract-address-components' was failing by invalid addresses.

The issue happened in `gnus-registry-spool-action' and invalid addresses
are passed by calling `message-fetch-field' on the buffer not narrowed
to message headers.

Below snippet reproduce the root issue:

(with-temp-buffer
  (save-excursion
    ;; mail header
    (insert "From: from@bar.com\n"
            "To: to@bar.com\n"
            "Subject: test\n")
    (newline)
    ;; mail body
    (insert "message\n"
            "Cc: >,@ <foo@bar.com>\n")) ;; by incorrect decode
  (gnus-registry-spool-action 1 "test"))

In stead of `message-fetch-field', calling `message-field-value' would
solve the problem since it ensures the buffer is narrowed at first.

diff -u "d:/msys64/mingw64/share/emacs/26.3/lisp/gnus/gnus-registry.el.orig" "d:/msys64/mingw64/share/emacs/26.3/lisp/gnus/gnus-registry.el"
--- d:/msys64/mingw64/share/emacs/26.3/lisp/gnus/gnus-registry.el.orig	2020-06-24 11:10:49.458397900 +0900
+++ d:/msys64/mingw64/share/emacs/26.3/lisp/gnus/gnus-registry.el	2020-06-23 11:08:23.170050000 +0900
@@ -405,10 +405,10 @@
   (let ((to (gnus-group-guess-full-name-from-command-method group))
           (recipients (or recipients
                           (gnus-registry-sort-addresses
-                           (or (message-fetch-field "cc") "")
-                           (or (message-fetch-field "to") ""))))
-          (subject (or subject (message-fetch-field "subject")))
-          (sender (or sender (message-fetch-field "from"))))
+                           (or (message-field-value "cc") "")
+                           (or (message-field-value "to") ""))))
+          (subject (or subject (message-field-value "subject")))
+          (sender (or sender (message-field-value "from"))))
       (when (and (stringp id) (string-match "\r$" id))
         (setq id (substring id 0 -1)))
       (gnus-message 7 "Gnus registry: article %s spooled to %s"

Diff finished.  Wed Jun 24 11:13:17 2020

Gnus v5.13
GNU Emacs 26.3 (build 1, x86_64-w64-mingw32)
 of 2020-04-04