tracing: Remove size restriction on hist trigger cmd error logging

Currently, hist trigger command error strings are restricted to a
length of MAX_FILTER_STR_VAL (256), which is too short for some
commands already seen in the wild (with cmd strings longer than that
showing up truncated in err_log).

Remove the restriction so that no hist trigger command error string is
ever truncated.

Link: https://lkml.kernel.org/r/0f9d46407222eaf6632cd3b417bc50a11f401b71.1643399022.git.zanussi@kernel.orgSigned-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

kernel/trace/trace_events_hist.c

@@ -727,11 +727,16 @@ static struct track_data *track_data_alloc(unsigned int key_len,
 	return data;
 }
 
-static char last_cmd[MAX_FILTER_STR_VAL];
+#define HIST_PREFIX "hist:"
+
+static char *last_cmd;
 static char last_cmd_loc[MAX_FILTER_STR_VAL];
 
 static int errpos(char *str)
 {
+	if (!str || !last_cmd)
+		return 0;
+
 	return err_pos(last_cmd, str);
 }
 
@@ -739,12 +744,19 @@ static void last_cmd_set(struct trace_event_file *file, char *str)
 {
 	const char *system = NULL, *name = NULL;
 	struct trace_event_call *call;
+	int len = 0;
 
 	if (!str)
 		return;
 
-	strcpy(last_cmd, "hist:");
-	strncat(last_cmd, str, MAX_FILTER_STR_VAL - 1 - sizeof("hist:"));
+	len += sizeof(HIST_PREFIX) + strlen(str) + 1;
+	kfree(last_cmd);
+	last_cmd = kzalloc(len, GFP_KERNEL);
+	if (!last_cmd)
+		return;
+
+	strcpy(last_cmd, HIST_PREFIX);
+	strncat(last_cmd, str, len - sizeof(HIST_PREFIX));
 
 	if (file) {
 		call = file->event_call;
@@ -757,18 +769,22 @@ static void last_cmd_set(struct trace_event_file *file, char *str)
 	}
 
 	if (system)
-		snprintf(last_cmd_loc, MAX_FILTER_STR_VAL, "hist:%s:%s", system, name);
+		snprintf(last_cmd_loc, MAX_FILTER_STR_VAL, HIST_PREFIX "%s:%s", system, name);
 }
 
-static void hist_err(struct trace_array *tr, u8 err_type, u8 err_pos)
+static void hist_err(struct trace_array *tr, u8 err_type, u16 err_pos)
 {
+	if (!last_cmd)
+		return;
+
 	tracing_log_err(tr, last_cmd_loc, last_cmd, err_text,
 			err_type, err_pos);
 }
 
 static void hist_err_clear(void)
 {
-	last_cmd[0] = '\0';
+	if (last_cmd)
+		last_cmd[0] = '\0';
 	last_cmd_loc[0] = '\0';
 }
 
@@ -5610,7 +5626,7 @@ static int event_hist_trigger_print(struct seq_file *m,
 	bool have_var = false;
 	unsigned int i;
 
-	seq_puts(m, "hist:");
+	seq_puts(m, HIST_PREFIX);
 
 	if (data->name)
 		seq_printf(m, "%s:", data->name);