diff options
| author | Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> | 2021-06-18 00:09:04 +0800 |
|---|---|---|
| committer | Miquel Raynal <miquel.raynal@bootlin.com> | 2021-07-16 00:49:17 +0200 |
| commit | 962bf783ef65d15b0f8ca9c33342cf3b20bf0d2e (patch) | |
| tree | cafab2ed58dab11f6d19b52a68a61d0749c488ad /drivers/mtd | |
| parent | 14f97f0b8e2b9950c028d0cb7311ffe26a3cc1c0 (diff) | |
mtd: break circular locks in register_mtd_blktrans
Syzbot reported a circular locking dependency:
https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb
This happens because of the following lock dependencies:
1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
loop_remove, which then calls del_gendisk; this also happens in
loop_exit which eventually calls loop_remove)
2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
__blkdev_get, which then calls blktrans_open)
3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
calls __register_blkdev)
4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
loop_probe)
Hence there's an overall dependency of:
loop_ctl_mutex ----------> bdev->bd_mutex
^ |
| |
| v
major_names_lock <--------- mtd_table_mutex
We can break this circular dependency by holding mtd_table_mutex only
for the required critical section in register_mtd_blktrans. This
avoids the mtd_table_mutex -> major_names_lock dependency.
Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
Co-developed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210617160904.570111-1-desmondcheongzx@gmail.com
Diffstat (limited to 'drivers/mtd')
| -rw-r--r-- | drivers/mtd/mtd_blkdevs.c | 8 |
1 files changed, 2 insertions, 6 deletions
diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c index 8f97a4fe6e93..31b208fb225e 100644 --- a/drivers/mtd/mtd_blkdevs.c +++ b/drivers/mtd/mtd_blkdevs.c @@ -526,14 +526,10 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr) if (!blktrans_notifier.list.next) register_mtd_user(&blktrans_notifier); - - mutex_lock(&mtd_table_mutex); - ret = register_blkdev(tr->major, tr->name); if (ret < 0) { printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n", tr->name, tr->major, ret); - mutex_unlock(&mtd_table_mutex); return ret; } @@ -543,12 +539,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr) tr->blkshift = ffs(tr->blksize) - 1; INIT_LIST_HEAD(&tr->devs); - list_add(&tr->list, &blktrans_majors); + mutex_lock(&mtd_table_mutex); + list_add(&tr->list, &blktrans_majors); mtd_for_each_device(mtd) if (mtd->type != MTD_ABSENT) tr->add_mtd(tr, mtd); - mutex_unlock(&mtd_table_mutex); return 0; } |