[PATCH 5.0 152/246] bcache: fix potential div-zero error of writeback_rate_i_term_inverse

[Greg Kroah-Hartman]

5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

[ 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@xxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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