efibc: Fix excessive stack footprint warning

GCC complains about a newly added file for the EFI Bootloader Control:

  drivers/firmware/efi/efibc.c: In function 'efibc_set_variable':
  drivers/firmware/efi/efibc.c:53:1: error: the frame size of 2272 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]

The problem is the declaration of a local variable of type struct
efivar_entry, which is by itself larger than the warning limit of 1024
bytes.

Use dynamic memory allocation instead of stack memory for the entry
object.

This patch also fixes a potential buffer overflow.

Reported-by: Ingo Molnar <mingo@kernel.org>
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jeremy Compostella <jeremy.compostella@intel.com>
[ Updated changelog to include GCC error ]
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/1462570771-13324-3-git-send-email-matt@codeblueprint.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/drivers/firmware/efi/efibc.c b/drivers/firmware/efi/efibc.c
index 2e0c7ccd9d9ec506baca32d51b5291e6d3fc467e..8dd0c7085e59799dce9064361e6e1ec7df4f0ccd 100644 (file)
--- a/drivers/firmware/efi/efibc.c
+++ b/drivers/firmware/efi/efibc.c
@@ -17,6 +17,7 @@
 #include <linux/efi.h>
 #include <linux/module.h>
 #include <linux/reboot.h>
+#include <linux/slab.h>
 
 static void efibc_str_to_str16(const char *str, efi_char16_t *str16)
 {
@@ -28,41 +29,52 @@ static void efibc_str_to_str16(const char *str, efi_char16_t *str16)
        str16[i] = '\0';
 }
 
-static void efibc_set_variable(const char *name, const char *value)
+static int efibc_set_variable(const char *name, const char *value)
 {
        int ret;
        efi_guid_t guid = LINUX_EFI_LOADER_ENTRY_GUID;
-       struct efivar_entry entry;
+       struct efivar_entry *entry;
        size_t size = (strlen(value) + 1) * sizeof(efi_char16_t);
 
-       if (size > sizeof(entry.var.Data))
+       if (size > sizeof(entry->var.Data)) {
                pr_err("value is too large");
+               return -EINVAL;
+       }
 
-       efibc_str_to_str16(name, entry.var.VariableName);
-       efibc_str_to_str16(value, (efi_char16_t *)entry.var.Data);
-       memcpy(&entry.var.VendorGuid, &guid, sizeof(guid));
+       entry = kmalloc(sizeof(*entry), GFP_KERNEL);
+       if (!entry) {
+               pr_err("failed to allocate efivar entry");
+               return -ENOMEM;
+       }
 
-       ret = efivar_entry_set(&entry,
+       efibc_str_to_str16(name, entry->var.VariableName);
+       efibc_str_to_str16(value, (efi_char16_t *)entry->var.Data);
+       memcpy(&entry->var.VendorGuid, &guid, sizeof(guid));
+
+       ret = efivar_entry_set(entry,
                               EFI_VARIABLE_NON_VOLATILE
                               | EFI_VARIABLE_BOOTSERVICE_ACCESS
                               | EFI_VARIABLE_RUNTIME_ACCESS,
-                              size, entry.var.Data, NULL);
+                              size, entry->var.Data, NULL);
        if (ret)
                pr_err("failed to set %s EFI variable: 0x%x\n",
                       name, ret);
+
+       kfree(entry);
+       return ret;
 }
 
 static int efibc_reboot_notifier_call(struct notifier_block *notifier,
                                      unsigned long event, void *data)
 {
        const char *reason = "shutdown";
+       int ret;
 
        if (event == SYS_RESTART)
                reason = "reboot";
 
-       efibc_set_variable("LoaderEntryRebootReason", reason);
-
-       if (!data)
+       ret = efibc_set_variable("LoaderEntryRebootReason", reason);
+       if (ret || !data)
                return NOTIFY_DONE;
 
        efibc_set_variable("LoaderEntryOneShot", (char *)data);