bcache: fix potential div-zero error of writeback_rate_i_term_inverse

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@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
index e4519326594f39e061b51b39cdd5effb85a96f00..0fad46d3a8bd75ce2ce347faa6b50b2c27f2c8ff 100644 (file)
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -302,7 +302,9 @@ 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);