From d5e06a1867210049bbfe27864ee0a40cfd9b1e9b Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Fri, 5 Jan 2018 16:26:00 -0800 Subject: [PATCH] loop: fix concurrent lo_open/lo_release MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit commit ae6650163c66a7eff1acd6eb8b0f752dcfa8eba5 upstream. 范龙飞 reports that KASAN can report a use-after-free in __lock_acquire. The reason is due to insufficient serialization in lo_release(), which will continue to use the loop device even after it has decremented the lo_refcnt to zero. In the meantime, another process can come in, open the loop device again as it is being shut down. Confusion ensues. CVE: CVE-2018-5344 Upstream-Status: Backport [https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.14.y&id=d5e06a1867210049bbfe27864ee0a40cfd9b1e9b] Reported-by: 范龙飞 Signed-off-by: Linus Torvalds Signed-off-by: Jens Axboe Cc: Ben Hutchings Signed-off-by: Greg Kroah-Hartman Signed-off-by: Andreas Wellving --- drivers/block/loop.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 85de67334695..a2a0dce5114e 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1576,9 +1576,8 @@ static int lo_open(struct block_device *bdev, fmode_t mode) return err; } -static void lo_release(struct gendisk *disk, fmode_t mode) +static void __lo_release(struct loop_device *lo) { - struct loop_device *lo = disk->private_data; int err; if (atomic_dec_return(&lo->lo_refcnt)) @@ -1605,6 +1604,13 @@ static void lo_release(struct gendisk *disk, fmode_t mode) mutex_unlock(&lo->lo_ctl_mutex); } +static void lo_release(struct gendisk *disk, fmode_t mode) +{ + mutex_lock(&loop_index_mutex); + __lo_release(disk->private_data); + mutex_unlock(&loop_index_mutex); +} + static const struct block_device_operations lo_fops = { .owner = THIS_MODULE, .open = lo_open, -- 2.20.1