linux-kernel - [PATCH AUTOSEL 5.0 162/262] bcache: fix potential div-zero error of writeback_rate_i_term

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Message-Id: <20190327180158.10245-162-sashal@kernel.org>
Date:   Wed, 27 Mar 2019 14:00:17 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Coly Li <colyli@...e.de>, Jens Axboe <axboe@...nel.dk>,
        Sasha Levin <sashal@...nel.org>, linux-bcache@...r.kernel.org
Subject: [PATCH AUTOSEL 5.0 162/262] bcache: fix potential div-zero error of writeback_rate_i_term_inverse

From: Coly Li <colyli@...e.de>

[ Upstream commit c3b75a2199cdbfc1c335155fe143d842604b1baa ]

dc->writeback_rate_i_term_inverse can be set via sysfs interface. It is
in type unsigned int, and convert from input string by d_strtoul(). The
problem is d_strtoul() does not check valid range of the input, if
4294967296 is written into sysfs file writeback_rate_i_term_inverse,
an overflow of unsigned integer will happen and value 0 is set to
dc->writeback_rate_i_term_inverse.

In writeback.c:__update_writeback_rate(), there are following lines of
code,
      integral_scaled = div_s64(dc->writeback_rate_integral,
                      dc->writeback_rate_i_term_inverse);
If dc->writeback_rate_i_term_inverse is set to 0 via sysfs interface,
a div-zero error might be triggered in the above code.

Therefore we need to add a range limitation in the sysfs interface,
this is what this patch does, use sysfs_stroul_clamp() to replace
d_strtoul() and restrict the input range in [1, UINT_MAX].

Signed-off-by: Coly Li <colyli@...e.de>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.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 f98cda32065d..28e0d5a5e25b 100644
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -287,7 +287,9 @@ STORE(__cached_dev)
 	sysfs_strtoul_clamp(writeback_rate_update_seconds,
 			    dc->writeback_rate_update_seconds,
 			    1, WRITEBACK_RATE_UPDATE_SECS_MAX);
-	d_strtoul(writeback_rate_i_term_inverse);
+	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);
 	d_strtoul_nonzero(writeback_rate_minimum);
 
-- 
2.19.1