[PATCH v2] libnvdimm/pmem: Fix blk_cleanup_disk() usage

[Dan Williams]

The queue_to_disk() helper can not be used after del_gendisk()
communicate @disk via the pgmap->owner.

Otherwise, queue_to_disk() returns NULL resulting in the splat below.

 Kernel attempted to read user page (330) - exploit attempt? (uid: 0)
 BUG: Kernel NULL pointer dereference on read at 0x00000330
 Faulting instruction address: 0xc000000000906344
 Oops: Kernel access of bad area, sig: 11 [#1]
 [..]
 NIP [c000000000906344] pmem_pagemap_cleanup+0x24/0x40
 LR [c0000000004701d4] memunmap_pages+0x1b4/0x4b0
 Call Trace:
 [c000000022cbb9c0] [c0000000009063c8] pmem_pagemap_kill+0x28/0x40 (unreliable)
 [c000000022cbb9e0] [c0000000004701d4] memunmap_pages+0x1b4/0x4b0
 [c000000022cbba90] [c0000000008b28a0] devm_action_release+0x30/0x50
 [c000000022cbbab0] [c0000000008b39c8] release_nodes+0x2f8/0x3e0
 [c000000022cbbb60] [c0000000008ac440] device_release_driver_internal+0x190/0x2b0
 [c000000022cbbba0] [c0000000008a8450] unbind_store+0x130/0x170

Reported-by: Sachin Sant <sachinp at linux.vnet.ibm.com>
Fixes: 87eb73b2ca7c ("nvdimm-pmem: convert to blk_alloc_disk/blk_cleanup_disk")
Link: http://lore.kernel.org/r/DFB75BA8-603F-4A35-880B-C5B23EF8FA7D@linux.vnet.ibm.com
Cc: Christoph Hellwig <hch at lst.de>
Cc: Ulf Hansson <ulf.hansson at linaro.org>
Cc: Jens Axboe <axboe at kernel.dk>
Signed-off-by: Dan Williams <dan.j.williams at intel.com>
---
Changes in v2 Improve the changelog.

 drivers/nvdimm/pmem.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 31f3c4bd6f72..fc6b78dd2d24 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -337,8 +337,9 @@ static void pmem_pagemap_cleanup(struct dev_pagemap *pgmap)
 {
 	struct request_queue *q =
 		container_of(pgmap->ref, struct request_queue, q_usage_counter);
+	struct pmem_device *pmem = pgmap->owner;
 
-	blk_cleanup_disk(queue_to_disk(q));
+	blk_cleanup_disk(pmem->disk);
 }
 
 static void pmem_release_queue(void *pgmap)
@@ -427,6 +428,7 @@ static int pmem_attach_disk(struct device *dev,
 	q = disk->queue;
 
 	pmem->disk = disk;
+	pmem->pgmap.owner = pmem;
 	pmem->pfn_flags = PFN_DEV;
 	pmem->pgmap.ref = &q->q_usage_counter;
 	if (is_nd_pfn(dev)) {