Re: [syzbot] KASAN: use-after-free Read in disk_part_iter_next (2)
From: Bart Van Assche <bvanassche@acm.org>
Date: 2021-03-22 22:21:59
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On 3/22/21 12:18 AM, Christoph Hellwig wrote:
quoted hunk ↗ jump to hunk
I've been running the reproducer on a KASAN enable VM for about 15 minutes now, but haven't been able to reproduce it. Is there a way to inject this proposed fix into the syzbot queue?diff --git a/block/partitions/core.c b/block/partitions/core.c index 1a7558917c47d6..f5d5872b89d57e 100644 --- a/block/partitions/core.c +++ b/block/partitions/core.c@@ -288,15 +288,12 @@ struct device_type part_type = { void delete_partition(struct block_device *part) { xa_erase(&part->bd_disk->part_tbl, part->bd_partno); - kobject_put(part->bd_holder_dir); - device_del(&part->bd_device); - - /* - * Remove the block device from the inode hash, so that it cannot be - * looked up any more even when openers still hold references. - */ remove_inode_hash(part->bd_inode); + synchronize_rcu(); + + kobject_put(part->bd_holder_dir); + device_del(&part->bd_device); put_device(&part->bd_device); }
Hi Christoph, disk_part_iter_next() calls bdgrab() before returning a pointer to a certain partition. 'part' is only freed if its reference count drops to zero. The function that frees the partition information, bdev_free_inode(), is invoked via call_rcu(). bdgrab() fails if the refcount of a partition is zero. Does that mean that it is not necessary to call synchronize_rcu() between xa_erase() and put_device()? Thanks, Bart.