linux-hardening - [PATCH] tracing: Use memset_startat() to zero struct trace

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Message-Id: <20211118202217.1285588-1-keescook@chromium.org>
Date:   Thu, 18 Nov 2021 12:22:17 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...hat.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] 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.

Signed-off-by: Kees Cook <keescook@...omium.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;
-- 
2.30.2