Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Yu Kuai <yukuai1@huaweicloud.com>
To:     tj@kernel.org, josef@toxicpanda.com, axboe@kernel.dk
Cc:     cgroups@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, yukuai3@huawei.com,
        yukuai1@huaweicloud.com, yi.zhang@huawei.com
Subject: [PATCH v3 4/5] blk-iocost: fix divide by 0 error in calc_lcoefs()
Date:   Mon, 26 Dec 2022 16:58:58 +0800
Message-Id: <20221226085859.2701195-5-yukuai1@huaweicloud.com>
In-Reply-To: <20221226085859.2701195-1-yukuai1@huaweicloud.com>
References: <20221226085859.2701195-1-yukuai1@huaweicloud.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

From: Li Nan <linan122@huawei.com>

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.

Fix the problem by setting basecost

Signed-off-by: Li Nan <linan122@huawei.com>
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/blk-iocost.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index f8726e20da20..c6b39024117b 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -866,9 +866,13 @@ static void calc_lcoefs(u64 bps, u64 seqiops, u64 randiops,
 
 	*page = *seqio = *randio = 0;
 
-	if (bps)
-		*page = DIV64_U64_ROUND_UP(VTIME_PER_SEC,
-					   DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE));
+	if (bps) {
+		if (bps >= U64_MAX - IOC_PAGE_SIZE)
+			*page = 1;
+		else
+			*page = DIV64_U64_ROUND_UP(VTIME_PER_SEC,
+					DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE));
+	}
 
 	if (seqiops) {
 		v = DIV64_U64_ROUND_UP(VTIME_PER_SEC, seqiops);
-- 
2.31.1