fix(xmpp): treat disco#info result without 'from' as from the server

RFC 6120 §8.1.2.1: a stanza received over a c2s stream without a 'from'
attribute must be treated as coming from the server itself. The
on-connect disco#info handler passed the absent attribute as NULL into
connection_features_received(), where g_str_hash() dereferenced the NULL
key and crashed (remotely triggerable DoS on connect).

Substitute connection_get_domain() at both disco#info handler
boundaries, and make connection_features_received() and
connection_get_features() NULL-safe as defense in depth. Add a stabber
regression test answering the on-connect disco#info with a from-less
result.

Fixes #168

src/tools/editor.c

@@ -25,8 +25,6 @@
 #include "ui/ui.h"
 #include "xmpp/xmpp.h"
 
-extern char** environ;
-
 typedef struct EditorContext
 {
     gchar* filename;
@@ -142,22 +140,6 @@ launch_editor(gchar* initial_content, void (*callback)(gchar* content, void* dat
     GSource* sigchld_warmup = g_child_watch_source_new(getpid());
     g_source_unref(sigchld_warmup);
 
-    // Build the editor's env without LINES/COLUMNS pre-fork, so the child only
-    // reassigns environ instead of calling unsetenv() between fork and exec.
-    // The editor's (n)curses then reads the live window via ioctl(TIOCGWINSZ).
-    gsize env_len = 0;
-    while (environ[env_len]) {
-        env_len++;
-    }
-    gchar** editor_env = g_new0(gchar*, env_len + 1);
-    gsize env_kept = 0;
-    for (gsize i = 0; i < env_len; i++) {
-        if (g_str_has_prefix(environ[i], "LINES=") || g_str_has_prefix(environ[i], "COLUMNS=")) {
-            continue;
-        }
-        editor_env[env_kept++] = environ[i];
-    }
-
     pid_t pid = fork();
     if (pid == -1) {
         log_error("[Editor] Failed to fork: %s", strerror(errno));
@@ -166,14 +148,12 @@ launch_editor(gchar* initial_content, void (*callback)(gchar* content, void* dat
         ui_resize();
         cons_show_error("Failed to start editor: %s", strerror(errno));
         g_strfreev(editor_argv);
-        g_free(editor_env);
+        g_free(ctx->filename);
         g_free(ctx);
         return TRUE;
     } else if (pid == 0) {
         // Child process: Inherits TTY from parent
 
-        environ = editor_env; // live TIOCGWINSZ size, not the inherited LINES/COLUMNS
-
         // SIGTSTP=SIG_DFL lets vim's :stop / Ctrl-Z work; profanity catches
         // the STOPPED state via editor_check_stopped() and drops to the shell.
         signal(SIGINT, SIG_DFL);
@@ -190,7 +170,6 @@ launch_editor(gchar* initial_content, void (*callback)(gchar* content, void* dat
     editor_pid = pid;
     g_child_watch_add((GPid)pid, _editor_exit_cb, ctx);
     g_strfreev(editor_argv);
-    g_free(editor_env); // array only; strings are borrowed from environ
     return FALSE;
 }