[balsa] autocrypt: fix crash when importing a half-broken key fails

[Albrecht Dreß <albrecht src gnome org>]

commit 8c32f9f9d6766b18ee62a61bf9376053d9b6ae73
Author: Albrecht Dreß <albrecht dress arcor de>
Date:   Wed Dec 9 20:58:06 2020 +0100

    autocrypt: fix crash when importing a half-broken key fails
    
    Return FALSE from extract_ac_keydata() if an Autocrypt header is present
    but contains a broken key, resulting in a failed import into GpgME.  The
    outcome of this is a crash in the caller due to an access to
    uninitialised memory.
    
    Signed-off-by: Albrecht Dreß <albrecht dress arcor de>

 libbalsa/autocrypt.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/libbalsa/autocrypt.c b/libbalsa/autocrypt.c
index af081fa83..4dacc2cfb 100644
--- a/libbalsa/autocrypt.c
+++ b/libbalsa/autocrypt.c
@@ -670,7 +670,7 @@ extract_ac_keydata(GMimeAutocryptHeader *autocrypt_header, ac_key_data_t *dest,
        gboolean success = FALSE;
 
        keydata = g_mime_autocrypt_header_get_keydata(autocrypt_header);
-       if (keydata) {
+       if (keydata != NULL) {
                gpgme_ctx_t ctx;
 
                dest->keydata = g_bytes_get_data(keydata, &dest->keysize);
@@ -696,11 +696,14 @@ extract_ac_keydata(GMimeAutocryptHeader *autocrypt_header, ac_key_data_t *dest,
                                        if ((key != NULL) && (key->subkeys != NULL)) {
                                                dest->fingerprint = g_strdup(key->subkeys->fpr);
                                                dest->expires = key->subkeys->expires;
+                                       } else {
+                                               success = FALSE;
                                        }
                                } else {
                                        g_warning("Failed to import or list key data for '%s': %s (%u keys, 
%u bad)",
                                                
g_mime_autocrypt_header_get_address_as_string(autocrypt_header),
                                                (gpg_error != NULL) ? gpg_error->message : "unknown", (keys 
!= NULL) ? g_list_length(keys) : 0U, bad_keys);
+                                       success = FALSE;
                                }
                                g_clear_error(&gpg_error);