linux-kernel - Re: [PATCH v2] libnvdimm/labels: Fix divide error in nd_label_data

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Message-ID: <20250321004147.i55w5i4whrar572x@offworld>
Date: Thu, 20 Mar 2025 17:41:47 -0700
From: Davidlohr Bueso <dave@...olabs.net>
To: Robert Richter <rrichter@....com>
Cc: Vishal Verma <vishal.l.verma@...el.com>,
	Ira Weiny <ira.weiny@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Alison Schofield <alison.schofield@...el.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
	Gregory Price <gourry@...rry.net>,
	Terry Bowman <terry.bowman@....com>,
	Pankaj Gupta <pankaj.gupta@....com>, nvdimm@...ts.linux.dev
Subject: Re: [PATCH v2] libnvdimm/labels: Fix divide error in
 nd_label_data_init()

On Thu, 20 Mar 2025, Robert Richter wrote:

>If a faulty CXL memory device returns a broken zero LSA size in its
>memory device information (Identify Memory Device (Opcode 4000h), CXL
>spec. 3.1, 8.2.9.9.1.1), a divide error occurs in the libnvdimm
>driver:
>
> Oops: divide error: 0000 [#1] PREEMPT SMP NOPTI
> RIP: 0010:nd_label_data_init+0x10e/0x800 [libnvdimm]
>
>Code and flow:
>
>1) CXL Command 4000h returns LSA size = 0
>2) config_size is assigned to zero LSA size (CXL pmem driver):
>
>drivers/cxl/pmem.c:             .config_size = mds->lsa_size,
>
>3) max_xfer is set to zero (nvdimm driver):
>
>drivers/nvdimm/label.c: max_xfer = min_t(size_t, ndd->nsarea.max_xfer, config_size);
>
>4) A subsequent DIV_ROUND_UP() causes a division by zero:
>
>drivers/nvdimm/label.c: /* Make our initial read size a multiple of max_xfer size */
>drivers/nvdimm/label.c: read_size = min(DIV_ROUND_UP(read_size, max_xfer) * max_xfer,
>drivers/nvdimm/label.c-                 config_size);
>
>Fix this by checking the config size parameter by extending an
>existing check.
>
>Signed-off-by: Robert Richter <rrichter@....com>
>Reviewed-by: Pankaj Gupta <pankaj.gupta@....com>
>Reviewed-by: Ira Weiny <ira.weiny@...el.com>

Reviewed-by: Davidlohr Bueso <dave@...olabs.net>