Re: [PATCH] tracing: Check for NULL field_name in __synth_event_add_val()

On Sun, 19 Feb 2023 15:46:24 -0600
Tom Zanussi [off-list ref] wrote:

No, because this code just above it makes sure you can't mix add_name
with add_next.  Once add_name is set it will return -EINVAL if
field_name is ever null after that, and add_name will never be changed
once set:

       /* can't mix add_next_synth_val() with add_synth_val() */
        if (field_name) {
                if (trace_state->add_next) {
                        ret = -EINVAL;
                        goto out;
                }
                trace_state->add_name = true;
        } else {
                if (trace_state->add_name) {
                        ret = -EINVAL;
                        goto out;
                }
                trace_state->add_next = true;
        }

quoted

 kernel/trace/trace_events_synth.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/trace_events_synth.c

b/kernel/trace/trace_events_synth.c
index 70bddb25d9c0..fa28c1da06d2 100644

--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c

@@ -1982,6 +1982,10 @@ static int __synth_event_add_val(const char

*field_name, u64 val,
 
        event = trace_state->event;
        if (trace_state->add_name) {
+               if (!field_name) {
+                       ret = -EINVAL;
+                       goto out;
+               }  

So if add_name is set here, it must also mean that field_name can't be
null, because of the above.

quoted

                for (i = 0; i < event->n_fields; i++) {
                        field = event->fields[i];
                        if (strcmp(field->name, field_name) == 0)  

And if field_name can't be null, then I don't see how this strcmp could
fail due to a null field_name.

So I don't see the need for this patch.  The bugzilla shows a compiler
warning when using -Wnonnull - could this just be a spurious gcc
warning?

Thanks, I should have caught that (I was even looking for that logic,
but still missed it). That's what I get for writing patches while jet-lagged :-p

-- Steve