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

[Jens Axboe]

On 6/7/21 5:52 PM, Dan Williams wrote:
> 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 0x0330
>  Faulting instruction address: 0xc0906344
>  Oops: Kernel access of bad area, sig: 11 [#1]
>  [..]
>  NIP [c0906344] pmem_pagemap_cleanup+0x24/0x40
>  LR [c04701d4] memunmap_pages+0x1b4/0x4b0
>  Call Trace:
>  [c00022cbb9c0] [c09063c8] pmem_pagemap_kill+0x28/0x40 
> (unreliable)
>  [c00022cbb9e0] [c04701d4] memunmap_pages+0x1b4/0x4b0
>  [c00022cbba90] [c08b28a0] devm_action_release+0x30/0x50
>  [c00022cbbab0] [c08b39c8] release_nodes+0x2f8/0x3e0
>  [c00022cbbb60] [c08ac440] 
> device_release_driver_internal+0x190/0x2b0
>  [c00022cbbba0] [c08a8450] unbind_store+0x130/0x170

Applied, thanks.

-- 
Jens Axboe

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

[Sachin Sant]

> Reported-by: Sachin Sant 
> Fixes: 87eb73b2ca7c ("nvdimm-pmem: convert to 
> blk_alloc_disk/blk_cleanup_disk")
> Link: 
> http://lore.kernel.org/r/dfb75ba8-603f-4a35-880b-c5b23ef8f...@linux.vnet.ibm.com
> Cc: Christoph Hellwig 
> Cc: Ulf Hansson 
> Cc: Jens Axboe 
> Signed-off-by: Dan Williams 
> ---

Thanks Dan. This patch fixes the reported crash for me.

Tested-by: Sachin Sant 
> 
> 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);

With this change variable ‘q' is no longer needed and can be removed.

drivers/nvdimm/pmem.c: In function 'pmem_pagemap_cleanup':
drivers/nvdimm/pmem.c:338:24: warning: unused variable 'q' [-Wunused-variable]
  struct request_queue *q =  
  ^
> + 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_usage_counter;
>   if (is_nd_pfn(dev)) {
> 

Thanks
-Sachin

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

[Christoph Hellwig]

Thanks Dan, this looks good to me:

Reviewed-by: Christoph Hellwig 

Jens, can you quickly pick this up?

[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 0x0330
 Faulting instruction address: 0xc0906344
 Oops: Kernel access of bad area, sig: 11 [#1]
 [..]
 NIP [c0906344] pmem_pagemap_cleanup+0x24/0x40
 LR [c04701d4] memunmap_pages+0x1b4/0x4b0
 Call Trace:
 [c00022cbb9c0] [c09063c8] pmem_pagemap_kill+0x28/0x40 (unreliable)
 [c00022cbb9e0] [c04701d4] memunmap_pages+0x1b4/0x4b0
 [c00022cbba90] [c08b28a0] devm_action_release+0x30/0x50
 [c00022cbbab0] [c08b39c8] release_nodes+0x2f8/0x3e0
 [c00022cbbb60] [c08ac440] 
device_release_driver_internal+0x190/0x2b0
 [c00022cbbba0] [c08a8450] unbind_store+0x130/0x170

Reported-by: Sachin Sant 
Fixes: 87eb73b2ca7c ("nvdimm-pmem: convert to blk_alloc_disk/blk_cleanup_disk")
Link: 
http://lore.kernel.org/r/dfb75ba8-603f-4a35-880b-c5b23ef8f...@linux.vnet.ibm.com
Cc: Christoph Hellwig 
Cc: Ulf Hansson 
Cc: Jens Axboe 
Signed-off-by: Dan Williams 
---
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_usage_counter;
if (is_nd_pfn(dev)) {