tracing: Fix parse_synth_field() error handling

synth_field_size() returns either a positive size or an error (zero or
a negative value). However, the existing code assumes the only error
value is 0. It doesn't handle negative error codes, as it assigns
directly to field->size (a size_t; unsigned), thereby interpreting the
error code as a valid size instead.

Do the test before assignment to field->size.

[ axelrasmussen@google.com: changelog addition, first paragraph above ]

Link: https://lkml.kernel.org/r/9b6946d9776b2eeb43227678158196de1c3c6e1d.1601848695.git.zanussi@kernel.org
Fixes: 4b147936fa50 (tracing: Add support for 'synthetic' events)
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Axel Rasmussen <axelrasmussen@google.com>
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index a9cd779..fa8a998 100644 (file)
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -465,6 +465,7 @@ static struct synth_field *parse_synth_field(int argc, const char **argv,
        struct synth_field *field;
        const char *prefix = NULL, *field_type = argv[0], *field_name, *array;
        int len, ret = 0;
+       ssize_t size;
 
        if (field_type[0] == ';')
                field_type++;
@@ -520,11 +521,12 @@ static struct synth_field *parse_synth_field(int argc, const char **argv,
                        field->type[len - 1] = '\0';
        }
 
-       field->size = synth_field_size(field->type);
-       if (!field->size) {
+       size = synth_field_size(field->type);
+       if (size <= 0) {
                ret = -EINVAL;
                goto free;
        }
+       field->size = size;
 
        if (synth_field_is_string(field->type))
                field->is_string = true;