Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Coly Li <colyli@suse.de>, Jens Axboe <axboe@kernel.dk>,
        Sasha Levin <sashal@kernel.org>, linux-bcache@vger.kernel.org
Subject: [PATCH AUTOSEL 5.0 262/262] bcache: fix potential div-zero error of writeback_rate_p_term_inverse
Date:   Wed, 27 Mar 2019 14:01:57 -0400
Message-Id: <20190327180158.10245-262-sashal@kernel.org>
In-Reply-To: <20190327180158.10245-1-sashal@kernel.org>
References: <20190327180158.10245-1-sashal@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Coly Li <colyli@suse.de>

[ Upstream commit 5b5fd3c94eef69dcfaa8648198e54c92e5687d6d ]

Current code already uses d_strtoul_nonzero() to convert input string
to an unsigned integer, to make sure writeback_rate_p_term_inverse
won't be zero value. But overflow may happen when converting input
string to an unsigned integer value by d_strtoul_nonzero(), then
dc->writeback_rate_p_term_inverse can still be set to 0 even if the
sysfs file input value is not zero, e.g. 4294967296 (a.k.a UINT_MAX+1).

If dc->writeback_rate_p_term_inverse is set to 0, it might cause a
dev-zero error in following code from __update_writeback_rate(),
	int64_t proportional_scaled =
		div_s64(error, dc->writeback_rate_p_term_inverse);

This patch replaces d_strtoul_nonzero() by sysfs_strtoul_clamp() and
limit the value range in [1, UINT_MAX]. Then the unsigned integer
overflow and dev-zero error can be avoided.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/md/bcache/sysfs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
index 28e0d5a5e25b..e5daf91310f6 100644
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -290,7 +290,9 @@ STORE(__cached_dev)
 	sysfs_strtoul_clamp(writeback_rate_i_term_inverse,
 			    dc->writeback_rate_i_term_inverse,
 			    1, UINT_MAX);
-	d_strtoul_nonzero(writeback_rate_p_term_inverse);
+	sysfs_strtoul_clamp(writeback_rate_p_term_inverse,
+			    dc->writeback_rate_p_term_inverse,
+			    1, UINT_MAX);
 	d_strtoul_nonzero(writeback_rate_minimum);
 
 	sysfs_strtoul_clamp(io_error_limit, dc->error_limit, 0, INT_MAX);
-- 
2.19.1