[PATCH v2 50/63] tracing: Use memset_startat() to zero struct trace_iterator

[Kees Cook]

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.

Cc: Steven Rostedt <rost...@goodmis.org>
Cc: Ingo Molnar <mi...@redhat.com>
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 kernel/trace/trace.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 13587e771567..9ff8c31975cd 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6691,9 +6691,7 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
                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;
-- 
2.30.2