[PATCH v3 11/16] tracing/filters: Check for trailing characters after newline in filter string

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

Each trace event or subsystem only holds a single filter, and
append_filter_err() / tracing_log_err() caret placement assumes a
single-line filter string. However, apply_event_filter() and
apply_subsystem_event_filter() only called strstrip(), which strips
trailing newlines but leaves embedded newlines intact.

An embedded newline in a filter string (for example inside 'CPUS{0\n"}')
causes cpulist_parse() / bitmap_parselist() to treat '\n' as the end of
the cpulist and ignore trailing characters before '}', desynchronizing
quote tracking between calc_stack() and parse_pred() and misaligning
error_log caret reporting.

Introduce an internal function filter_check_newline() to convert the
first newline to NUL and check that the rest of the input contains no
non-whitespace characters. If any non-whitespace character follows the
newline, report it as an invalid input error (-EINVAL).

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
Changes in v3:
 - Introduce filter_check_newline() to convert the first newline to
   NUL and reject any non-whitespace characters after the newline with
   an invalid input error (-EINVAL).
---
 kernel/trace/trace_events_filter.c |   37 ++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 9d1446464058..f3c18324b07a 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -2441,6 +2441,31 @@ static int process_system_preds(struct trace_subsystem_dir *dir,
 	return -ENOMEM;
 }
 
+/*
+ * Convert the first newline to '\0' and check that the rest of the input
+ * contains no non-whitespace characters.
+ */
+static int filter_check_newline(char *str)
+{
+	char *p;
+
+	if (!str)
+		return 0;
+
+	p = strchr(str, '\n');
+	if (!p)
+		return 0;
+
+	*p++ = '\0';
+	while (*p) {
+		if (!isspace(*p))
+			return -EINVAL;
+		p++;
+	}
+
+	return 0;
+}
+
 static int create_filter_start(char *filter_string, bool set_str,
 			       struct filter_parse_error **pse,
 			       struct event_filter **filterp)
@@ -2452,6 +2477,10 @@ static int create_filter_start(char *filter_string, bool set_str,
 	if (WARN_ON_ONCE(*pse || *filterp))
 		return -EINVAL;
 
+	err = filter_check_newline(filter_string);
+	if (err)
+		return err;
+
 	filter = kzalloc_obj(*filter);
 	if (filter && set_str) {
 		filter->filter_string = kstrdup(filter_string, GFP_KERNEL);
@@ -2570,6 +2599,10 @@ int apply_event_filter(struct trace_event_file *file, char *filter_string)
 	if (file->flags & EVENT_FILE_FL_FREED)
 		return -ENODEV;
 
+	err = filter_check_newline(filter_string);
+	if (err)
+		return err;
+
 	if (!strcmp(strstrip(filter_string), "0")) {
 		filter_disable(file);
 		filter = event_filter(file);
@@ -2624,6 +2657,10 @@ int apply_subsystem_event_filter(struct trace_subsystem_dir *dir,
 	if (!dir->nr_events)
 		return -ENODEV;
 
+	err = filter_check_newline(filter_string);
+	if (err)
+		return err;
+
 	if (!strcmp(strstrip(filter_string), "0")) {
 		filter_free_subsystem_preds(dir, tr);
 		remove_filter_string(system->filter);