From 897366537fb65e87755b822360c230354c3fc73b Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Mon, 26 Feb 2018 13:01:40 +0100 Subject: genhd: Fix use after free in __blkdev_get() When two blkdev_open() calls race with device removal and recreation, __blkdev_get() can use looked up gendisk after it is freed: CPU0 CPU1 CPU2 del_gendisk(disk); bdev_unhash_inode(inode); blkdev_open() blkdev_open() bdev = bd_acquire(inode); - creates and returns new inode bdev = bd_acquire(inode); - returns the same inode __blkdev_get(devt) __blkdev_get(devt) disk = get_gendisk(devt); - got structure of device going away disk = get_gendisk(devt); - got new device structure if (!bdev->bd_openers) { does the first open } if (!bdev->bd_openers) - false } else { put_disk_and_module(disk) - remember this was old device - this was last ref and disk is now freed } disk_unblock_events(disk); -> oops Fix the problem by making sure we drop reference to disk in __blkdev_get() only after we are really done with it. Reported-by: Hou Tao Tested-by: Hou Tao Signed-off-by: Jan Kara Signed-off-by: Jens Axboe --- fs/block_dev.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'fs/block_dev.c') diff --git a/fs/block_dev.c b/fs/block_dev.c index 1dbbf847911a..fe41a76769fa 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -1409,6 +1409,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part) int ret; int partno; int perm = 0; + bool first_open = false; if (mode & FMODE_READ) perm |= MAY_READ; @@ -1435,6 +1436,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part) disk_block_events(disk); mutex_lock_nested(&bdev->bd_mutex, for_part); if (!bdev->bd_openers) { + first_open = true; bdev->bd_disk = disk; bdev->bd_queue = disk->queue; bdev->bd_contains = bdev; @@ -1520,14 +1522,15 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part) if (ret) goto out_unlock_bdev; } - /* only one opener holds refs to the module and disk */ - put_disk_and_module(disk); } bdev->bd_openers++; if (for_part) bdev->bd_part_count++; mutex_unlock(&bdev->bd_mutex); disk_unblock_events(disk); + /* only one opener holds refs to the module and disk */ + if (!first_open) + put_disk_and_module(disk); return 0; out_clear: -- cgit v1.2.3-55-g7522