busybox: ash history option -c to delete command history from memory

release/src/router/busybox/include/libbb.h

@@ -1567,6 +1567,7 @@ line_input_t *new_line_input_t(int flags) FAST_FUNC;
  */
 int read_line_input(line_input_t *st, const char *prompt, char *command, int maxsize, int timeout) FAST_FUNC;
 void show_history(const line_input_t *st) FAST_FUNC;
+void clear_history(line_input_t *st) FAST_FUNC;
 # if ENABLE_FEATURE_EDITING_SAVE_ON_EXIT
 void save_history(line_input_t *st);
 # endif

release/src/router/busybox/libbb/lineedit.c

@@ -1341,6 +1341,41 @@ void FAST_FUNC show_history(const line_input_t *st)
 		printf("%4d %s\n", i, st->history[i]);
 }
 
+// the function secure_memory_wipe(), aka OPENSSL_cleanse(), was stolen from 
+// OpenSSL because we need a way to securely wipe the ash command history from
+// memory without the compiler optimizing it away
+static unsigned char secure_memory_wipe_ctr = 0;
+static void secure_memory_wipe(void *ptr, size_t len)
+{
+	unsigned char *p = ptr;
+	size_t loop = len, ctr = secure_memory_wipe_ctr;
+	while(loop--)
+		{
+		*(p++) = (unsigned char)ctr;
+		ctr += (17 + ((size_t)p & 0xF));
+		}
+	p=memchr(ptr, (unsigned char)ctr, len);
+	if(p)
+		ctr += (63 + (size_t)p);
+	secure_memory_wipe_ctr = (unsigned char)ctr;
+}
+
+/* Clears command history. Used by shell 'history' builtins */
+void FAST_FUNC clear_history(line_input_t *st)
+{
+	int i;
+
+	if (!st)
+		return;
+
+	for (i = 0; i < st->cnt_history; i++) {
+		secure_memory_wipe(st->history[i], strlen(st->history[i]));
+		free(st->history[i]);
+		st->history[i] = NULL;
+	}
+	st->cur_history = st->cnt_history = 0;
+}
+
 # if ENABLE_FEATURE_EDITING_SAVEHISTORY
 /* We try to ensure that concurrent additions to the history
  * do not overwrite each other.

release/src/router/busybox/shell/ash.c

@@ -12611,6 +12611,10 @@ helpcmd(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
 static int FAST_FUNC
 historycmd(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
 {
+	if (nextopt("c") != '\0') {
+		clear_history(line_input_state);
+		return EXIT_SUCCESS;
+	}
 	show_history(line_input_state);
 	return EXIT_SUCCESS;
 }

release/src/router/busybox/shell/hush.c

@@ -8715,6 +8715,15 @@ static int FAST_FUNC builtin_help(char **argv UNUSED_PARAM)
 #if MAX_HISTORY && ENABLE_FEATURE_EDITING
 static int FAST_FUNC builtin_history(char **argv UNUSED_PARAM)
 {
+	unsigned opts;
+
+	opts = getopt32(argv, "!c");
+	if (opts == (unsigned)-1)
+		return EXIT_FAILURE;
+	if (opts & 1) {
+		clear_history(G.line_input_state);
+		return EXIT_SUCCESS;
+	}
 	show_history(G.line_input_state);
 	return EXIT_SUCCESS;
 }