dell-wmi: Clean up hotkey table size check

Checking the table for a minimum size of 7 bytes makes no sense: any valid
hotkey table has a size that's a multiple of 4.

Clean this up: replace the hardcoded header length with a sizeof and
change the check to ignore an empty hotkey table.  The only behavior
change is that a 7-byte table (which is nonsensical) will now be
treated as absent instead of as valid but empty.

Reported-by: Jean Delvare <jdelvare@suse.de>
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 d6ae69e..32808a4 100644 (file)
--- a/drivers/platform/x86/dell-wmi.c
+++ b/drivers/platform/x86/dell-wmi.c
@@ -351,13 +351,24 @@ static void __init handle_dmi_entry(const struct dmi_header *dm,
        if (results->err || results->keymap)
                return;         /* We already found the hotkey table. */
 
-       if (dm->type != 0xb2 || dm->length <= 6)
+       if (dm->type != 0xb2)
                return;
 
        table = container_of(dm, struct dell_bios_hotkey_table, header);
 
-       hotkey_num = (table->header.length - 4) /
+       hotkey_num = (table->header.length -
+                     sizeof(struct dell_bios_hotkey_table)) /
                                sizeof(struct dell_bios_keymap_entry);
+       if (hotkey_num < 1) {
+               /*
+                * Historically, dell-wmi would ignore a DMI entry of
+                * fewer than 7 bytes.  Sizes between 4 and 8 bytes are
+                * nonsensical (both the header and all entries are 4
+                * bytes), so we approximate the old behavior by
+                * ignoring tables with fewer than one entry.
+                */
+               return;
+       }
 
        keymap = kcalloc(hotkey_num + 1, sizeof(struct key_entry), GFP_KERNEL);
        if (!keymap) {