From: Yiyuan guo <yguoaz@gmail.com>
To: axboe@kernel.dk
Cc: linux-block@vger.kernel.org, Yiyuan guo <yguoaz@gmail.com>
Subject: A possible divide by zero bug in blk_mq_map_queues
Date: Fri, 14 May 2021 16:28:47 +0800 [thread overview]
Message-ID: <CAM7=BFrvCdsW1xekOb9QAdVkhRAU6kdg1g98OUz6YYyXOuMZRg@mail.gmail.com> (raw)
In block/blk-mq-cpumap.c, blk_mq_map_queues has the following code:
int blk_mq_map_queues(struct blk_mq_queue_map *qmap) {
...
unsigned int nr_queues = qmap->nr_queues;
unsigned q = 0;
...
for_each_present_cpu(cpu) {
if (q >= nr_queues)
break;
...
}
for_each_possible_cpu(cpu) {
...
if (q < nr_queues) {
map[cpu] = queue_index(qmap, nr_queues, q++);
} else {
...
if (first_sibling == cpu)
map[cpu] = queue_index(qmap, nr_queues, q++);
}
}
}
if qmap->nr_queues equals to zero when entering the function, then by
passing zero to function queue_index we have a divide by zero bug:
static int queue_index(struct blk_mq_queue_map *qmap,
unsigned int nr_queues, const int q)
{
return qmap->queue_offset + (q % nr_queues);
}
It seems possible to me that qmap->nr_queues may equal zero because
this field is explicitly checked in other functions.
For example, in the function blk_mq_map_swqueue (block/blk-mq.c),
there is a check comparing nr_queues with 0:
for (j = 0; j < set->nr_maps; j++) {
if (!set->map[j].nr_queues) {
...
continue;
}
...
}
next reply other threads:[~2021-05-14 8:29 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-14 8:28 Yiyuan guo [this message]
2021-05-14 8:34 ` A possible divide by zero bug in blk_mq_map_queues Hannes Reinecke
2021-05-14 9:16 ` [PATCH] block: add protection for divide by zero " Yiyuan GUO
2021-05-14 9:24 ` Hannes Reinecke
2021-05-14 9:38 ` [PATCH v2] " Yiyuan GUO
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