Re: [PATCH v2 2/2] of/pci: Fix memory leak in of_pci_get_host_bridge_resources

[jeffy]

Hi Rob & Dmitry,

On 03/24/2017 06:58 AM, Dmitry Torokhov wrote:
> On Thu, Mar 23, 2017 at 3:07 PM, Rob Herring <robh@xxxxxxxxxx> wrote:
> > On Thu, Mar 23, 2017 at 3:12 AM, Jeffy Chen <jeffy.chen@xxxxxxxxxxxxxx> wrote:
> > > Currently we only free the allocated resource struct when error.
> > > This would cause memory leak after pci_free_resource_list.
> > >
> > > Signed-off-by: Jeffy Chen <jeffy.chen@xxxxxxxxxxxxxx>
> > > ---
> > >
> > > Changes in v2:
> > > Don't change the resource_list_create_entry's behavior.
> > >
> > >   drivers/of/of_pci.c | 57 +++++++++++++++++++++++------------------------------
> > >   1 file changed, 25 insertions(+), 32 deletions(-)
> > >
> > > diff --git a/drivers/of/of_pci.c b/drivers/of/of_pci.c
> > > index 0ee42c3..a0ec246 100644
> > > --- a/drivers/of/of_pci.c
> > > +++ b/drivers/of/of_pci.c
> > > @@ -190,8 +190,7 @@ int of_pci_get_host_bridge_resources(struct device_node *dev,
> > >                          struct list_head *resources, resource_size_t *io_base)
> > >   {
> > >          struct resource_entry *window;
> > > -       struct resource *res;
> > > -       struct resource *bus_range;
> > > +       struct resource res;
> > >          struct of_pci_range range;
> > >          struct of_pci_range_parser parser;
> > >          char range_type[4];
> > > @@ -200,24 +199,24 @@ int of_pci_get_host_bridge_resources(struct device_node *dev,
> > >          if (io_base)
> > >                  *io_base = (resource_size_t)OF_BAD_ADDR;
> > >
> > > -       bus_range = kzalloc(sizeof(*bus_range), GFP_KERNEL);
> > > -       if (!bus_range)
> > > -               return -ENOMEM;
> > > -
> > >          pr_info("host bridge %s ranges:\n", dev->full_name);
> > >
> > > -       err = of_pci_parse_bus_range(dev, bus_range);
> > > +       err = of_pci_parse_bus_range(dev, &res);
> > >          if (err) {
> > > -               bus_range->start = busno;
> > > -               bus_range->end = bus_max;
> > > -               bus_range->flags = IORESOURCE_BUS;
> > > -               pr_info("  No bus range found for %s, using %pR\n",
> > > -                       dev->full_name, bus_range);
> > > +               res.start = busno;
> > > +               res.end = bus_max;
> > > +               res.flags = IORESOURCE_BUS;
> > > +               pr_info("  No bus range found for %s\n", dev->full_name);
> > >          } else {
> > > -               if (bus_range->end > bus_range->start + bus_max)
> > > -                       bus_range->end = bus_range->start + bus_max;
> > > +               if (res.end > res.start + bus_max)
> > > +                       res.end = res.start + bus_max;
> > > +       }
> > > +       window = pci_add_resource(resources, NULL);
> > > +       if (!window) {
> > > +               err = -ENOMEM;
> > > +               goto parse_failed;
> > >          }
> > > -       pci_add_resource(resources, bus_range);
> > > +       *window->res = res;
> >
> > Well, now this seems racy. You add a blank resource to the list first
> > and then fill it in.
>
> Huh? There is absolutely no guarantees for concurrent access here.
> pcI_add_resource_offset() first adds a resource and then modifies
> offset. Here we add an empty resource and then fill it in.
currently, we are using of_pci_get_host_bridge_resources in this pattern:

create resource list:
        LIST_HEAD(res);
...
add resources into the list:
        err = of_pci_get_host_bridge_resources(dev->of_node, 0, 0xff,
                                               &res, &io_base);
...
walk over the list:
        /* Get the I/O and memory ranges from DT */
        resource_list_for_each_entry(win, &res) {

so only of_pci_get_host_bridge_resources is accessing this list at that 
time.

and an empty resource is harmless i think(with zero size and flags) ;)

maybe i should add some comments in the patch

> Thanks.