fix segfault

src/memline.c

@@ -2494,6 +2494,18 @@ ml_sync_all(int check_file, int check_char)
 		|| buf->b_ml.ml_mfp->mf_fd < 0)
 	    continue;			    // no file
 
+	// Safety Check
+	if (crypt_method_is_sodium(crypt_get_method_nr(buf))
+					&& *buf->b_p_key != NUL)
+	{
+	    // close the swapfile
+	    mf_close_file(buf, TRUE);
+	    buf->b_p_swf = FALSE;
+	    vim_free(buf->b_p_key);
+	    buf->b_p_key = empty_option;
+	    continue;
+	}
+
 	ml_flush_line(buf);		    // flush buffered line
 					    // flush locked block
 	(void)ml_find_line(buf, (linenr_T)0, ML_FLUSH);
@@ -5571,6 +5583,15 @@ ml_crypt_prepare(memfile_T *mfp, off_T offset, int reading)
     if (*key == NUL)
 	return NULL;
 
+    // safety check
+    if (crypt_method_is_sodium(method_nr))
+    {
+	// close the swapfile
+	mf_close_file(buf, TRUE);
+	buf->b_p_swf = FALSE;
+	return NULL;
+    }
+
     if (method_nr == CRYPT_M_ZIP)
     {
 	// For PKzip: Append the offset to the key, so that we use a different

src/testdir/test_crypt.vim

@@ -392,4 +392,24 @@ func Test_crypt_set_key_changes_buffer()
   call delete('Xtest1.txt')
 endfunc
 
+func Test_crypt_set_key_segfault()
+  CheckFeature sodium
+
+  defer delete('Xtest2.txt')
+  new Xtest2.txt
+  call setline(1, 'nothing')
+  set cryptmethod=xchacha20
+  set key=foobar
+  w
+  new Xtest3
+  put ='other content'
+  setl modified
+  sil! preserve
+  bw!
+
+  set cryptmethod&
+  set key=
+  bwipe!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab