bpf: sanitize bpf tracepoint access

during bpf program loading remember the last byte of ctx access
and at the time of attaching the program to tracepoint check that
the program doesn't access bytes beyond defined in tracepoint fields

This also disallows access to __dynamic_array fields, but can be
relaxed in the future.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 18 insertions, 0 deletions

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 05ddc0820771..ced963049e0a 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -204,6 +204,24 @@ static void trace_destroy_fields(struct trace_event_call *call)
 	}
 }
 
+/*
+ * run-time version of trace_event_get_offsets_<call>() that returns the last
+ * accessible offset of trace fields excluding __dynamic_array bytes
+ */
+int trace_event_get_offsets(struct trace_event_call *call)
+{
+	struct ftrace_event_field *tail;
+	struct list_head *head;
+
+	head = trace_get_fields(call);
+	/*
+	 * head->next points to the last field with the largest offset,
+	 * since it was added last by trace_define_field()
+	 */
+	tail = list_first_entry(head, struct ftrace_event_field, link);
+	return tail->offset + tail->size;
+}
+
 int trace_event_raw_init(struct trace_event_call *call)
 {
 	int id;