tracing: Use memset_startat() to zero struct trace_iterator

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Use memset_startat() to avoid confusing memset() about writing beyond
the target struct member.

Link: https://lkml.kernel.org/r/20211118202217.1285588-1-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f9139dc..e3c80cf 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6706,9 +6706,7 @@ waitagain:
                cnt = PAGE_SIZE - 1;
 
        /* reset all but tr, trace, and overruns */
-       memset(&iter->seq, 0,
-              sizeof(struct trace_iterator) -
-              offsetof(struct trace_iterator, seq));
+       memset_startat(iter, 0, seq);
        cpumask_clear(iter->started);
        trace_seq_init(&iter->seq);
        iter->pos = -1;