From: Dan Williams Date: Tue, 29 Dec 2015 22:02:29 +0000 (-0800) Subject: block: fix del_gendisk() vs blkdev_ioctl crash X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=ac34f15e0c6d2fd58480052b6985f6991fb53bcc;p=GitHub%2FLineageOS%2Fandroid_kernel_motorola_exynos9610.git block: fix del_gendisk() vs blkdev_ioctl crash When tearing down a block device early in its lifetime, userspace may still be performing discovery actions like blkdev_ioctl() to re-read partitions. The nvdimm_revalidate_disk() implementation depends on disk->driverfs_dev to be valid at entry. However, it is set to NULL in del_gendisk() and fatally this is happening *before* the disk device is deleted from userspace view. There's no reason for del_gendisk() to clear ->driverfs_dev. That device is the parent of the disk. It is guaranteed to not be freed until the disk, as a child, drops its ->parent reference. We could also fix this issue locally in nvdimm_revalidate_disk() by using disk_to_dev(disk)->parent, but lets fix it globally since ->driverfs_dev follows the lifetime of the parent. Longer term we should probably just add a @parent parameter to add_disk(), and stop carrying this pointer in the gendisk. BUG: unable to handle kernel NULL pointer dereference at (null) IP: [] nvdimm_revalidate_disk+0x18/0x90 [libnvdimm] CPU: 2 PID: 538 Comm: systemd-udevd Tainted: G O 4.4.0-rc5 #2257 [..] Call Trace: [] rescan_partitions+0x87/0x2c0 [] ? __lock_is_held+0x49/0x70 [] __blkdev_reread_part+0x72/0xb0 [] blkdev_reread_part+0x25/0x40 [] blkdev_ioctl+0x4fd/0x9c0 [] ? current_kernel_time64+0x69/0xd0 [] block_ioctl+0x3d/0x50 [] do_vfs_ioctl+0x308/0x560 [] ? __audit_syscall_entry+0xb1/0x100 [] ? do_audit_syscall_entry+0x66/0x70 [] SyS_ioctl+0x79/0x90 [] entry_SYSCALL_64_fastpath+0x12/0x76 Reported-by: Robert Hu Signed-off-by: Dan Williams --- diff --git a/block/genhd.c b/block/genhd.c index e5cafa51567c..1a971bebbbfe 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -664,7 +664,6 @@ void del_gendisk(struct gendisk *disk) kobject_put(disk->part0.holder_dir); kobject_put(disk->slave_dir); - disk->driverfs_dev = NULL; if (!sysfs_deprecated) sysfs_remove_link(block_depr, dev_name(disk_to_dev(disk))); pm_runtime_set_memalloc_noio(disk_to_dev(disk), false);