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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Colin Ian King <colin.king@canonical.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.9 405/757] refperf: Avoid null pointer dereference when buf fails to allocate
Date:   Tue, 27 Oct 2020 14:50:55 +0100
Message-Id: <20201027135509.572088475@linuxfoundation.org>
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From: Colin Ian King <colin.king@canonical.com>

[ Upstream commit 58db5785b0d76be4582a32a7900acce88e691d36 ]

Currently in the unlikely event that buf fails to be allocated it
is dereferenced a few times.  Use the errexit flag to determine if
buf should be written to to avoid the null pointer dereferences.

Addresses-Coverity: ("Dereference after null check")
Fixes: f518f154ecef ("refperf: Dynamically allocate experiment-summary output buffer")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/rcu/refscale.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index d9291f883b542..952595c678b37 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -546,9 +546,11 @@ static int main_func(void *arg)
 	// Print the average of all experiments
 	SCALEOUT("END OF TEST. Calculating average duration per loop (nanoseconds)...\n");
 
-	buf[0] = 0;
-	strcat(buf, "\n");
-	strcat(buf, "Runs\tTime(ns)\n");
+	if (!errexit) {
+		buf[0] = 0;
+		strcat(buf, "\n");
+		strcat(buf, "Runs\tTime(ns)\n");
+	}
 
 	for (exp = 0; exp < nruns; exp++) {
 		u64 avg;
-- 
2.25.1