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block: ensure the bdi is freed after inode_detach_wb

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inode_detach_wb references the "main" bdi of the inode.  With the
recent change to move the bdi from the request_queue to the gendisk
this causes a guaranteed use after free when using certain cgroup
configurations.  The big itself is older through as any non-default
inode reference (e.g. an open file descriptor) could have injected
this use after free even before that.

Fixes: 52ebea749a ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks")
Reported-by: Qian Cai <quic_qiancai@quicinc.com>
Reported-by: syzbot <syzbot+1fb38bb7d3ce0fa3e1c4@syzkaller.appspotmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210816122614.601358-3-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2021-08-16 14:26:14 +02:00 committed by Jens Axboe
parent 9451aa0aac
commit 889c05cc58
2 changed files with 4 additions and 4 deletions
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1
block/genhd.c
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@ -1084,7 +1084,6 @@ static void disk_release(struct device *dev)
might_sleep();
bdi_put(disk->bdi);
disk_release_events(disk);
kfree(disk->random);
xa_destroy(&disk->part_tbl);

7
fs/block_dev.c
View File

@ -812,8 +812,11 @@ static void bdev_free_inode(struct inode *inode)
free_percpu(bdev->bd_stats);
kfree(bdev->bd_meta_info);
if (!bdev_is_partition(bdev))
if (!bdev_is_partition(bdev)) {
if (bdev->bd_disk && bdev->bd_disk->bdi)
bdi_put(bdev->bd_disk->bdi);
kfree(bdev->bd_disk);
}
if (MAJOR(bdev->bd_dev) == BLOCK_EXT_MAJOR)
blk_free_ext_minor(MINOR(bdev->bd_dev));
@ -833,8 +836,6 @@ static void bdev_evict_inode(struct inode *inode)
truncate_inode_pages_final(&inode->i_data);
invalidate_inode_buffers(inode); /* is it needed here? */
clear_inode(inode);
/* Detach inode from wb early as bdi_put() may free bdi->wb */
inode_detach_wb(inode);
}
static const struct super_operations bdev_sops = {