[PATCH -next 1/2] blk-iocost: fix divide by 0 error in calc_lcoefs()

Li Nan
2022-11-24T13:45:35Z

echo max of u64 to cost.model can cause divide by 0 error.

# echo 8:0 rbps=18446744073709551615 > /sys/fs/cgroup/io.cost.model

divide error: 0000 [#1] PREEMPT SMP
RIP: 0010:calc_lcoefs+0x4c/0xc0
Call Trace:
<TASK>
ioc_refresh_params+0x2b3/0x4f0
ioc_cost_model_write+0x3cb/0x4c0
? _copy_from_iter+0x6d/0x6c0
? kernfs_fop_write_iter+0xfc/0x270
cgroup_file_write+0xa0/0x200
kernfs_fop_write_iter+0x17d/0x270
vfs_write+0x414/0x620
ksys_write+0x73/0x160
__x64_sys_write+0x1e/0x30
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

calc_lcoefs() uses the input value of cost.model in DIV_ROUND_UP_ULL,
overflow would happen if bps plus IOC_PAGE_SIZE is greater than
ULLONG_MAX, it can cause divide by 0 error.I_LCOEF_MAX is introduced to
prevent it.

Signed-off-by: Li Nan <linan122@huawei.com>
---
block/blk-iocost.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index f01359906c83..a38a5324bf10 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -306,6 +306,9 @@ enum {
IOC_PAGE_SIZE = 1 << IOC_PAGE_SHIFT,
IOC_SECT_TO_PAGE_SHIFT = IOC_PAGE_SHIFT - SECTOR_SHIFT,

+ /* avoid overflow */
+ I_LCOEF_MAX = ULLONG_MAX - IOC_PAGE_SIZE,
+
/* if apart further than 16M, consider randio for linear model */
LCOEF_RANDIO_PAGES = 4096,
};
@@ -3406,6 +3409,8 @@ static ssize_t ioc_cost_model_write(struct kernfs_open_file *of, char *input,
goto einval;
if (match_u64(&args[0], &v))
goto einval;
+ if (v > I_LCOEF_MAX)
+ goto einval;
u[tok] = v;
user = true;
}
--
2.31.1