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From:   Kees Cook <keescook@chromium.org>
To:     linux-kernel@vger.kernel.org
Cc:     Kees Cook <keescook@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
        dri-devel@lists.freedesktop.org, linux-staging@lists.linux.dev,
        linux-block@vger.kernel.org, linux-kbuild@vger.kernel.org,
        clang-built-linux@googlegroups.com,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        linux-hardening@vger.kernel.org
Subject: [PATCH v2 50/63] tracing: Use memset_startat() to zero struct trace_iterator
Date:   Tue, 17 Aug 2021 23:05:20 -0700
Message-Id: <20210818060533.3569517-51-keescook@chromium.org>
In-Reply-To: <20210818060533.3569517-1-keescook@chromium.org>
References: <20210818060533.3569517-1-keescook@chromium.org>
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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 <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Kees Cook <keescook@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