From: Vegard Nossum <vegard.nossum@oracle.com>
To: Tejun Heo <tj@kernel.org>
Cc: Rabin Vincent <rabin@rab.in>, Jens Axboe <axboe@fb.com>,
Jan Kara <jack@suse.cz>, Al Viro <viro@zeniv.linux.org.uk>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH] bdev: fix NULL pointer dereference in sync()/close() race
Date: Mon, 29 Aug 2016 23:33:41 +0200 [thread overview]
Message-ID: <14b09a61-8e8f-166d-45b9-7dd07922286e@oracle.com> (raw)
In-Reply-To: <20160829195540.GE28713@mtj.duckdns.org>
On 08/29/2016 09:55 PM, Tejun Heo wrote:
> On Sat, Aug 27, 2016 at 11:30:22AM +0200, Vegard Nossum wrote:
>> If people who are more savvy in block/fs code could ack the locking bits
>> I think we should apply the patch ASAP because it's an easy local DOS if
>> you have (open/read) access to any block device.
>
> I think the right thing to do there is doing blkdev_get() /
> blkdev_put() around func() invocation in iterate_bdevs() rather than
> holding bd_mutex across the callback. Can you please verify whether
> that works?
Didn't work for me, I kept getting use-after-free in __blkdev_get() on
bdev->bd_invalidated after it calls bdev->bd_disk->fops->open(). I tried
a few related things without much luck.
The only thing that worked for me without holding the mutex across the
call was this:
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 08ae993..586d745 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1885,6 +1885,7 @@ void iterate_bdevs(void (*func)(struct
block_device *, void *), void *arg)
spin_lock(&blockdev_superblock->s_inode_list_lock);
list_for_each_entry(inode, &blockdev_superblock->s_inodes, i_sb_list) {
struct address_space *mapping = inode->i_mapping;
+ struct block_device *bdev;
spin_lock(&inode->i_lock);
if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW) ||
@@ -1906,7 +1907,19 @@ void iterate_bdevs(void (*func)(struct
block_device *, void *), void *arg)
iput(old_inode);
old_inode = inode;
- func(I_BDEV(inode), arg);
+ bdev = I_BDEV(inode);
+
+ mutex_lock(&bdev->bd_mutex);
+ bdev->bd_openers++;
+ bdev->bd_holders++;
+ mutex_unlock(&bdev->bd_mutex);
+
+ func(bdev, arg);
+
+ mutex_lock(&bdev->bd_mutex);
+ bdev->bd_openers--;
+ bdev->bd_holders--;
+ mutex_unlock(&bdev->bd_mutex);
spin_lock(&blockdev_superblock->s_inode_list_lock);
}
I'm guessing that's too simple to work in general (especially when you
bring in partitions and stuff; I'm just opening /dev/sr0 in my reproducer).
It's been a long day, I'll have a look tomorrow and see if I didn't just
do something stupid.
Vegard
next prev parent reply other threads:[~2016-08-29 21:34 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-27 7:07 [PATCH] bdev: fix NULL pointer dereference in sync()/close() race Vegard Nossum
2016-08-27 9:03 ` Rabin Vincent
2016-08-27 9:30 ` Vegard Nossum
2016-08-29 19:55 ` Tejun Heo
2016-08-29 20:49 ` Vegard Nossum
2016-08-29 20:54 ` Tejun Heo
2016-08-29 21:33 ` Vegard Nossum [this message]
2016-08-29 23:49 ` Tejun Heo
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