[PATCH 51/64] tracing: Use struct_group() 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.

Add struct_group() to mark region of struct trace_iterator that should
be initialized to zero.

Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 include/linux/trace_events.h | 26 ++++++++++++++------------
 kernel/trace/trace.c         |  4 +---
 2 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index ad413b382a3c..cadad77fe524 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -101,18 +101,20 @@ struct trace_iterator {
        bool                    snapshot;
 
        /* The below is zeroed out in pipe_read */
-       struct trace_seq        seq;
-       struct trace_entry      *ent;
-       unsigned long           lost_events;
-       int                     leftover;
-       int                     ent_size;
-       int                     cpu;
-       u64                     ts;
-
-       loff_t                  pos;
-       long                    idx;
-
-       /* All new field here will be zeroed out in pipe_read */
+       struct_group(init,
+               struct trace_seq        seq;
+               struct trace_entry      *ent;
+               unsigned long           lost_events;
+               int                     leftover;
+               int                     ent_size;
+               int                     cpu;
+               u64                     ts;
+
+               loff_t                  pos;
+               long                    idx;
+
+               /* All new field here will be zeroed out in pipe_read */
+       );
 };
 
 enum trace_iter_flags {
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c59dd35a6da5..9f83864b0be6 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(&iter->init, 0, sizeof(iter->init));
        cpumask_clear(iter->started);
        trace_seq_init(&iter->seq);
        iter->pos = -1;
-- 
2.30.2