Re: [PATCH v2 8/9] tracing/filters: Terminate filter string at first newline

[Steven Rostedt <rostedt@goodmis.org>]

On Sun, 25 Oct 2026 17:38:22 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> 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 call 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.
> 
> Terminate filter_string at the first '\n' in apply_event_filter(),
> apply_subsystem_event_filter(), and create_filter_start() so only the
> first line is parsed.

How about also checking if there's any non white space after the newline,
and if so, fail the filter outright with -EINVAL?

-- Steve


> 
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> ---
>  kernel/trace/trace_events_filter.c |   15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
> index 8d7fb6e9d7f8..14afcca7a444 100644
> --- a/kernel/trace/trace_events_filter.c
> +++ b/kernel/trace/trace_events_filter.c
> @@ -2426,10 +2426,15 @@ static int create_filter_start(char *filter_string, bool set_str,
>  	struct event_filter *filter;
>  	struct filter_parse_error *pe = NULL;
>  	int err = 0;
> +	char *p;
>  
>  	if (WARN_ON_ONCE(*pse || *filterp))
>  		return -EINVAL;
>  
> +	p = strchr(filter_string, '\n');
> +	if (p)
> +		*p = '\0';
> +
>  	filter = kzalloc_obj(*filter);
>  	if (filter && set_str) {
>  		filter->filter_string = kstrdup(filter_string, GFP_KERNEL);
> @@ -2543,11 +2548,16 @@ int apply_event_filter(struct trace_event_file *file, char *filter_string)
>  {
>  	struct trace_event_call *call = file->event_call;
>  	struct event_filter *filter = NULL;
> +	char *p;
>  	int err;
>  
>  	if (file->flags & EVENT_FILE_FL_FREED)
>  		return -ENODEV;
>  
> +	p = strchr(filter_string, '\n');
> +	if (p)
> +		*p = '\0';
> +
>  	if (!strcmp(strstrip(filter_string), "0")) {
>  		filter_disable(file);
>  		filter = event_filter(file);
> @@ -2595,6 +2605,7 @@ int apply_subsystem_event_filter(struct trace_subsystem_dir *dir,
>  	struct trace_array *tr = dir->tr;
>  	struct event_filter *filter = NULL;
>  	int err = 0;
> +	char *p;
>  
>  	guard(mutex)(&event_mutex);
>  
> @@ -2602,6 +2613,10 @@ int apply_subsystem_event_filter(struct trace_subsystem_dir *dir,
>  	if (!dir->nr_events)
>  		return -ENODEV;
>  
> +	p = strchr(filter_string, '\n');
> +	if (p)
> +		*p = '\0';
> +
>  	if (!strcmp(strstrip(filter_string), "0")) {
>  		filter_free_subsystem_preds(dir, tr);
>  		remove_filter_string(system->filter);