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

[Andy Lutomirski <luto@kernel.org>]

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.

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