dell-wmi: Stop storing pointers to DMI tables

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.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>

diff --git a/drivers/platform/x86/dell-wmi.c b/drivers/platform/x86/dell-wmi.c
index 368e193..d6ae69e 100644 (file)
--- a/drivers/platform/x86/dell-wmi.c
+++ b/drivers/platform/x86/dell-wmi.c
@@ -120,7 +120,10 @@ 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 = {
@@ -337,20 +340,34 @@ 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_entry(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 <
@@ -379,11 +396,12 @@ static const struct key_entry * __init dell_wmi_prepare_new_keymap(void)
 
        keymap[hotkey_num].type = KE_END;
 
-       return keymap;
+       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();
@@ -394,20 +412,31 @@ 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;
-               }
+       if (dmi_walk(handle_dmi_entry, &dmi_results)) {
+               /*
+                * Historically, dell-wmi ignored dmi_walk errors.  A failure
+                * is certainly surprising, but it probably just indicates
+                * a very old laptop.
+                */
+               pr_warn("no DMI; using the old-style hotkey interface\n");
+       }
+
+       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, keymap, NULL);
+               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);
@@ -434,15 +463,6 @@ 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);
-       }
-}
-
 /*
  * Descriptor buffer is 128 byte long and contains:
  *
@@ -524,8 +544,6 @@ static int __init dell_wmi_init(void)
        if (err)
                return err;
 
-       dmi_walk(find_hk_type, NULL);
-
        err = dell_wmi_input_setup();
        if (err)
                return err;