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SubjectRe: [PATCH] dell-wmi: Stop storing pointers to DMI tables
On Monday 11 January 2016 13:58:20 Andy Lutomirski wrote:
> On Sun, Jan 3, 2016 at 6:52 AM, Andy Lutomirski <luto@kernel.org> 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@vger.kernel.org
> > Signed-off-by: Andy Lutomirski <luto@kernel.org>
> > ---
> >
> > 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 Rohár
pali.rohar@gmail.com

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