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

[Dan Carpenter]

On Mon, Jul 15, 2024 at 04:28:15PM +1000, Michael Ellerman wrote:
> Ma Ke <make24@xxxxxxxxxxx> writes:
> > 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@xxxxxxxxxxxxxxx
> > Fixes: 14baf4d9c739 ("cxl: Add guest-specific code")
> > Signed-off-by: Ma Ke <make24@xxxxxxxxxxx>

The bug is real and the fix looks okay to me. I'm surprised that Smatch doesn't
print a warning about "size" being uninitialized.  I must not have it enabled
in the .configs that I test.  But I also wouldn't have reported that because
it's from 2016 so it's too old.

> > ---
> > 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.
> 

You're a domain expert so I trust you, but as a static checker person, there is
no way I'd feel comfortable sending a patch like that...  It's way too
complicated and I wouldn't be able to test it.  If this were my patch I would
ask you to handle send that patch and give me Reported-by credit.

regards,
dan carpenter