Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables

[Pali RohÃr]

On Monday 11 January 2016 13:58:20 Andy Lutomirski wrote:
> On Sun, Jan 3, 2016 at 6:52 AM, Andy Lutomirski <luto@xxxxxxxxxx> wrote:
> > The dmi_walk function maps the DMI table, walks it, and unmaps it.
> > This means that the dell_bios_hotkey_table that find_hk_type stores
> > points to unmapped memory by the time it gets read.
> >
> > I've been able to trigger crashes caused by the stale pointer a
> > couple of times, but never on a stock kernel.
> >
> > Fix it by generating the keymap in the dmi_walk callback instead of
> > storing a pointer.
> 
> Quick ping: has anyone had a chance to look at this?
> 
> --Andy
> 

Hi Andy, I looked at this patch, but I think some people from -mm or DMI
code should look at it as it is memory problem... We also has one in
dell-laptop.ko (wrong API usage) and so -mm people could know it better.

> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
> > ---
> >
> > This seems to work on my laptop.  It applies to platform-drivers-x86/for-next.
> >
> > drivers/platform/x86/dell-wmi.c | 69 +++++++++++++++++++++++++----------------
> >  1 file changed, 42 insertions(+), 27 deletions(-)
> >
> > diff --git a/drivers/platform/x86/dell-wmi.c b/drivers/platform/x86/dell-wmi.c
> > index 57402c4c394e..52db2721d7e3 100644
> > --- a/drivers/platform/x86/dell-wmi.c
> > +++ b/drivers/platform/x86/dell-wmi.c
> > @@ -116,7 +116,10 @@ struct dell_bios_hotkey_table {
> >
> >  };
> >
> > -static const struct dell_bios_hotkey_table *dell_bios_hotkey_table;
> > +struct dell_dmi_results {
> > +       int err;
> > +       struct key_entry *keymap;
> > +};
> >
> >  /* Uninitialized entries here are KEY_RESERVED == 0. */
> >  static const u16 bios_to_linux_keycode[256] __initconst = {
> > @@ -316,20 +319,34 @@ static void dell_wmi_notify(u32 value, void *context)
> >         kfree(obj);
> >  }
> >
> > -static const struct key_entry * __init dell_wmi_prepare_new_keymap(void)
> > +static void __init handle_dmi_table(const struct dmi_header *dm,
> > +                                   void *opaque)
> >  {
> > -       int hotkey_num = (dell_bios_hotkey_table->header.length - 4) /
> > -                               sizeof(struct dell_bios_keymap_entry);
> > +       struct dell_dmi_results *results = opaque;
> > +       struct dell_bios_hotkey_table *table;
> >         struct key_entry *keymap;
> > -       int i;
> > +       int hotkey_num, i;
> > +
> > +       if (results->err || results->keymap)
> > +               return;         /* We already found the hotkey table. */
> > +
> > +       if (dm->type != 0xb2 || dm->length <= 6)
> > +               return;
> > +
> > +       table = container_of(dm, struct dell_bios_hotkey_table, header);
> > +
> > +       hotkey_num = (table->header.length - 4) /
> > +                               sizeof(struct dell_bios_keymap_entry);
> >
> >         keymap = kcalloc(hotkey_num + 1, sizeof(struct key_entry), GFP_KERNEL);
> > -       if (!keymap)
> > -               return NULL;
> > +       if (!keymap) {
> > +               results->err = -ENOMEM;
> > +               return;
> > +       }
> >
> >         for (i = 0; i < hotkey_num; i++) {
> >                 const struct dell_bios_keymap_entry *bios_entry =
> > -                                       &dell_bios_hotkey_table->keymap[i];
> > +                                       &table->keymap[i];
> >
> >                 /* Uninitialized entries are 0 aka KEY_RESERVED. */
> >                 u16 keycode = (bios_entry->keycode <
> > @@ -358,11 +375,13 @@ static const struct key_entry * __init dell_wmi_prepare_new_keymap(void)
> >
> >         keymap[hotkey_num].type = KE_END;
> >
> > -       return keymap;
> > +       results->err = 0;
> > +       results->keymap = keymap;
> >  }
> >
> >  static int __init dell_wmi_input_setup(void)
> >  {
> > +       struct dell_dmi_results dmi_results = {};
> >         int err;
> >
> >         dell_wmi_input_dev = input_allocate_device();
> > @@ -373,20 +392,26 @@ static int __init dell_wmi_input_setup(void)
> >         dell_wmi_input_dev->phys = "wmi/input0";
> >         dell_wmi_input_dev->id.bustype = BUS_HOST;
> >
> > -       if (dell_new_hk_type) {
> > -               const struct key_entry *keymap = dell_wmi_prepare_new_keymap();
> > -               if (!keymap) {
> > -                       err = -ENOMEM;
> > -                       goto err_free_dev;
> > -               }
> > +       err = dmi_walk(handle_dmi_table, &dmi_results);
> > +       if (err)
> > +               goto err_free_dev;
> >
> > -               err = sparse_keymap_setup(dell_wmi_input_dev, keymap, NULL);
> > +       if (dmi_results.err) {
> > +               err = dmi_results.err;
> > +               goto err_free_dev;
> > +       }
> > +
> > +       if (dmi_results.keymap) {
> > +               dell_new_hk_type = true;
> > +
> > +               err = sparse_keymap_setup(dell_wmi_input_dev,
> > +                                         dmi_results.keymap, NULL);
> >
> >                 /*
> >                  * Sparse keymap library makes a copy of keymap so we
> >                  * don't need the original one that was allocated.
> >                  */
> > -               kfree(keymap);
> > +               kfree(dmi_results.keymap);
> >         } else {
> >                 err = sparse_keymap_setup(dell_wmi_input_dev,
> >                                           dell_wmi_legacy_keymap, NULL);
> > @@ -413,15 +438,6 @@ static void dell_wmi_input_destroy(void)
> >         input_unregister_device(dell_wmi_input_dev);
> >  }
> >
> > -static void __init find_hk_type(const struct dmi_header *dm, void *dummy)
> > -{
> > -       if (dm->type == 0xb2 && dm->length > 6) {
> > -               dell_new_hk_type = true;
> > -               dell_bios_hotkey_table =
> > -                       container_of(dm, struct dell_bios_hotkey_table, header);
> > -       }
> > -}
> > -
> >  static int __init dell_wmi_init(void)
> >  {
> >         int err;
> > @@ -432,7 +448,6 @@ static int __init dell_wmi_init(void)
> >                 return -ENODEV;
> >         }
> >
> > -       dmi_walk(find_hk_type, NULL);
> >         acpi_video = acpi_video_get_backlight_type() != acpi_backlight_vendor;
> >
> >         err = dell_wmi_input_setup();
> > --
> > 2.5.0
> >
> 
> 
> 

-- 
Pali RohÃr
pali.rohar@xxxxxxxxx