efi/capsule: Move 'capsule' to the stack in efi_capsule_supported()

Dan Carpenter reports that passing the address of the pointer to the
kmalloc()'d memory for 'capsule' is dangerous:

 "drivers/firmware/efi/capsule.c:109 efi_capsule_supported()
  warn: did you mean to pass the address of 'capsule'

   108
   109          status = efi.query_capsule_caps(&capsule, 1, &max_size, reset);
                                                ^^^^^^^^
  If we modify capsule inside this function call then at the end of the
  function we aren't freeing the original pointer that we allocated."

Ard Biesheuvel noted that we don't even need to call kmalloc() since the
object we allocate isn't very big and doesn't need to persist after the
function returns.

Place 'capsule' on the stack instead.

Suggested-by: Ard Biesheuvel <[email protected]>
Reported-by: Dan Carpenter <[email protected]>
Signed-off-by: Matt Fleming <[email protected]>
Acked-by: Ard Biesheuvel <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Bryan O'Donoghue <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Kweh Hock Leong <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: joeyli <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

1 files changed, 11 insertions, 18 deletions

diff --git a/drivers/firmware/efi/capsule.c b/drivers/firmware/efi/capsule.c
index e530540f368c..53b9fd2293ee 100644
--- a/drivers/firmware/efi/capsule.c
+++ b/drivers/firmware/efi/capsule.c
@@ -86,33 +86,26 @@ bool efi_capsule_pending(int *reset_type)
  */
 int efi_capsule_supported(efi_guid_t guid, u32 flags, size_t size, int *reset)
 {
-	efi_capsule_header_t *capsule;
+	efi_capsule_header_t capsule;
+	efi_capsule_header_t *cap_list[] = { &capsule };
 	efi_status_t status;
 	u64 max_size;
-	int rv = 0;
 
 	if (flags & ~EFI_CAPSULE_SUPPORTED_FLAG_MASK)
 		return -EINVAL;
 
-	capsule = kmalloc(sizeof(*capsule), GFP_KERNEL);
-	if (!capsule)
-		return -ENOMEM;
-
-	capsule->headersize = capsule->imagesize = sizeof(*capsule);
-	memcpy(&capsule->guid, &guid, sizeof(efi_guid_t));
-	capsule->flags = flags;
+	capsule.headersize = capsule.imagesize = sizeof(capsule);
+	memcpy(&capsule.guid, &guid, sizeof(efi_guid_t));
+	capsule.flags = flags;
 
-	status = efi.query_capsule_caps(&capsule, 1, &max_size, reset);
-	if (status != EFI_SUCCESS) {
-		rv = efi_status_to_err(status);
-		goto out;
-	}
+	status = efi.query_capsule_caps(cap_list, 1, &max_size, reset);
+	if (status != EFI_SUCCESS)
+		return efi_status_to_err(status);
 
 	if (size > max_size)
-		rv = -ENOSPC;
-out:
-	kfree(capsule);
-	return rv;
+		return -ENOSPC;
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(efi_capsule_supported);