Re: [PATCH v2 1/2] libnvdimm, region: fix flush hint detection crash

[Jeff Moyer <jmoyer@redhat.com>]

Dan Williams <dan.j.williams@intel.com> writes:

> In the case where a dimm does not have any associated flush hints the
> ndrd->flush_wpq array may be uninitialized leading to crashes with the
> following signature:
>
>  BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
>  IP: region_visible+0x10f/0x160 [libnvdimm]
>
>  Call Trace:
>   internal_create_group+0xbe/0x2f0
>   sysfs_create_groups+0x40/0x80
>   device_add+0x2d8/0x650
>   nd_async_device_register+0x12/0x40 [libnvdimm]
>   async_run_entry_fn+0x39/0x170
>   process_one_work+0x212/0x6c0
>   ? process_one_work+0x197/0x6c0
>   worker_thread+0x4e/0x4a0
>   kthread+0x10c/0x140
>   ? process_one_work+0x6c0/0x6c0
>   ? kthread_create_on_node+0x60/0x60
>   ret_from_fork+0x31/0x40

Sorry for being dense, but I'm having a tough time connecting the dots,
here.  How does region_visible trip over the missing (not uninitialized,
you're actually walking off the end of the structure) wpq_flush array?

Anyway, the fix looks valid.

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>

Thanks,
Jeff

>
> Cc: <stable@vger.kernel.org>
> Fixes: f284a4f23752 ("libnvdimm: introduce nvdimm_flush() and nvdimm_has_flush()")
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  drivers/nvdimm/region_devs.c |   11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
> index 8de5a04644a1..24abceda986a 100644
> --- a/drivers/nvdimm/region_devs.c
> +++ b/drivers/nvdimm/region_devs.c
> @@ -1000,17 +1000,20 @@ EXPORT_SYMBOL_GPL(nvdimm_flush);
>   */
>  int nvdimm_has_flush(struct nd_region *nd_region)
>  {
> -	struct nd_region_data *ndrd = dev_get_drvdata(&nd_region->dev);
>  	int i;
>  
>  	/* no nvdimm == flushing capability unknown */
>  	if (nd_region->ndr_mappings == 0)
>  		return -ENXIO;
>  
> -	for (i = 0; i < nd_region->ndr_mappings; i++)
> -		/* flush hints present, flushing required */
> -		if (ndrd_get_flush_wpq(ndrd, i, 0))
> +	for (i = 0; i < nd_region->ndr_mappings; i++) {
> +		struct nd_mapping *nd_mapping = &nd_region->mapping[i];
> +		struct nvdimm *nvdimm = nd_mapping->nvdimm;
> +
> +		/* flush hints present / available */
> +		if (nvdimm->num_flush)
>  			return 1;
> +	}
>  
>  	/*
>  	 * The platform defines dimm devices without hints, assume
>
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