Re: [PATCH v5 02/11] block: Block Device Filtering Mechanism

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Hi,

在 2023/07/18 1:39, Sergei Shtepa 写道:
Hi.

On 7/12/23 14:34, Yu Kuai wrote:
Subject:
Re: [PATCH v5 02/11] block: Block Device Filtering Mechanism
From:
Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>
Date:
7/12/23, 14:34

To:
Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>, Sergei Shtepa <sergei.shtepa@xxxxxxxxx>, axboe@xxxxxxxxx, hch@xxxxxxxxxxxxx, corbet@xxxxxxx, snitzer@xxxxxxxxxx
CC:
viro@xxxxxxxxxxxxxxxxxx, brauner@xxxxxxxxxx, dchinner@xxxxxxxxxx, willy@xxxxxxxxxxxxx, dlemoal@xxxxxxxxxx, linux@xxxxxxxxxxxxxx, jack@xxxxxxx, ming.lei@xxxxxxxxxx, linux-block@xxxxxxxxxxxxxxx, linux-doc@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, Donald Buczek <buczek@xxxxxxxxxxxxx>, "yukuai (C)" <yukuai3@xxxxxxxxxx>


Hi,

在 2023/07/12 18:04, Yu Kuai 写道:
Hi,

在 2023/07/11 10:02, Yu Kuai 写道:

+static bool submit_bio_filter(struct bio *bio)
+{
+    if (bio_flagged(bio, BIO_FILTERED))
+        return false;
+
+    bio_set_flag(bio, BIO_FILTERED);
+    return bio->bi_bdev->bd_filter->ops->submit_bio(bio);
+}
+
   static void __submit_bio(struct bio *bio)
   {
+    /*
+     * If there is a filter driver attached, check if the BIO needs to go to
+     * the filter driver first, which can then pass on the bio or consume it.
+     */
+    if (bio->bi_bdev->bd_filter && submit_bio_filter(bio))
+        return;
+
       if (unlikely(!blk_crypto_bio_prep(&bio)))
           return;

...

+static void __blkfilter_detach(struct block_device *bdev)
+{
+    struct blkfilter *flt = bdev->bd_filter;
+    const struct blkfilter_operations *ops = flt->ops;
+
+    bdev->bd_filter = NULL;
+    ops->detach(flt);
+    module_put(ops->owner);
+}
+
+void blkfilter_detach(struct block_device *bdev)
+{
+    if (bdev->bd_filter) {
+        blk_mq_freeze_queue(bdev->bd_queue);

And this is not sate as well, for bio-based device, q_usage_counter is
not grabbed while submit_bio_filter() is called, hence there is a risk
of uaf from submit_bio_filter().

And there is another question, can blkfilter_detach() from
del_gendisk/delete_partiton and ioctl concurrent? I think it's a
problem.


Yes, it looks like if two threads execute the blkfilter_detach() function,
then a problem is possible. The blk_mq_freeze_queue() function does not
block threads.
But for this, it is necessary that the IOCTL for the block device and
its removal are performed simultaneously. Is this possible?

I think it's possible, ioctl only requires to open the disk/partition,
and it won't block disk removal:

t1:			t2:

open dev
ioctl
			remove dev
			 del_gendisk
 blkfilter_detach	  blkfilter_detach


I suppose that using mutex bdev->bd_disk->open_mutex in
blkfilter_ioctl_attach(), blkfilter_ioctl_detach() and
blkfilter_ioctl_ctl() can fix the problem. What do you think?

I think it's ok, and blkfilter ioctl must check disk_live() while
holding the lock.

Thanks,
Kuai



Thanks,
Kuai

Thanks,
Kuai

.


.





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