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Subject[for-linus][PATCH 2/3] tracing: Use memset_startat() to zero struct trace_iterator
From: Kees Cook <keescook@chromium.org>

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>
---
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 f9139dc1262c..e3c80cfd4eec 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6706,9 +6706,7 @@ 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;
--
2.33.0
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