Re: [PATCH v4] cxl: Fix possible null pointer dereference in read_handle()

Michael Ellerman
2024-07-19T01:23:11Z

Ma Ke <make24@iscas.ac.cn> writes:
>> Michael Ellerman<mpe@ellerman.id.au> wrote:
>> > In read_handle(), of_get_address() may return NULL if getting address and
>> > size of the node failed. When of_read_number() uses prop to handle
>> > conversions between different byte orders, it could lead to a null pointer
>> > dereference. Add NULL check to fix potential issue.
>> >
>> > Found by static analysis.
>> >
>> > Cc: stable@vger.kernel.org
>> > Fixes: 14baf4d9c739 ("cxl: Add guest-specific code")
>> > Signed-off-by: Ma Ke <make24@iscas.ac.cn>
>> > ---
>> > Changes in v4:
>> > - modified vulnerability description according to suggestions, making the
>> > process of static analysis of vulnerabilities clearer. No active research
>> > on developer behavior.
>> > Changes in v3:
>> > - fixed up the changelog text as suggestions.
>> > Changes in v2:
>> > - added an explanation of how the potential vulnerability was discovered,
>> > but not meet the description specification requirements.
>> > ---
>> > drivers/misc/cxl/of.c | 2 +-
>> > 1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/misc/cxl/of.c b/drivers/misc/cxl/of.c
>> > index bcc005dff1c0..d8dbb3723951 100644
>> > --- a/drivers/misc/cxl/of.c
>> > +++ b/drivers/misc/cxl/of.c
>> > @@ -58,7 +58,7 @@ static int read_handle(struct device_node *np, u64 *handle)
>> >
>> > /* Get address and size of the node */
>> > prop = of_get_address(np, 0, &size, NULL);
>> > - if (size)
>> > + if (!prop || size)
>> > return -EINVAL;
>> >
>> > /* Helper to read a big number; size is in cells (not bytes) */
>>
>> If you expand the context this could just use of_property_read_reg(),
>> something like below.
>>
>> cheers
>>
>>
>> diff --git a/drivers/misc/cxl/of.c b/drivers/misc/cxl/of.c
>> index bcc005dff1c0..a184855b2a7b 100644
>> --- a/drivers/misc/cxl/of.c
>> +++ b/drivers/misc/cxl/of.c
>> @@ -53,16 +53,15 @@ static const __be64 *read_prop64_dword(const struct device_node *np,
>>
>> static int read_handle(struct device_node *np, u64 *handle)
>> {
>> - const __be32 *prop;
>> u64 size;
>> +
>> + if (of_property_read_reg(np, 0, handle, &size))
>> + return -EINVAL;
>>
>> - /* Get address and size of the node */
>> - prop = of_get_address(np, 0, &size, NULL);
>> + // Size must be zero per PAPR+ v2.13 § C.6.19
>> if (size)
>> return -EINVAL;
>>
>> - /* Helper to read a big number; size is in cells (not bytes) */
>> - *handle = of_read_number(prop, of_n_addr_cells(np));
>> return 0;
>> }

> Thank you for discussing and guiding me on the vulnerability I submitted.
> I've carefully read through your conversation with Dan Carpenter. I'm
> uncertain whether to use my patch or the one you provided. Could you please
> advise on which patch would be more appropriate?
> Looking forward to your reply.

Your patch is OK, I'll send an ack.

If we want to refactor it to use of_property_read_reg() we can do that
in future - though this code will probably be removed in the not too
distant future anyway.

cheers