Code: static struct key *construct_key_and_link(struct keyring_search_context *ctx,
					  const char *callout_info,
					  size_t callout_len,
					  void *aux,
					  struct key *dest_keyring,
					  unsigned long flags)
{
	struct key_user *user;
	struct key *key;
	int ret;
 
 	kenter("");
 
 	user = key_user_lookup(current_fsuid());
 	if (!user)
 		return ERR_PTR(-ENOMEM);

	construct_get_dest_keyring(&dest_keyring);

	ret = construct_alloc_key(ctx, dest_keyring, flags, user, &key);
	key_user_put(user);

	if (ret == 0) {
		ret = construct_key(key, callout_info, callout_len, aux,
				    dest_keyring);
		if (ret < 0) {
			kdebug("cons failed");
			goto construction_failed;
		}
	} else if (ret == -EINPROGRESS) {
		ret = 0;
	} else {
		goto couldnt_alloc_key;
	}

	key_put(dest_keyring);
	kleave(" = key %d", key_serial(key));
	return key;

construction_failed:
	key_negate_and_link(key, key_negative_timeout, NULL, NULL);
	key_put(key);
couldnt_alloc_key:
	key_put(dest_keyring);
	kleave(" = %d", ret);
	return ERR_PTR(ret);
}

Vulnerability Type: DoS 
CWE ID: CWE-20
Summary: The key_gc_unused_keys function in security/keys/gc.c in the Linux kernel through 4.2.6 allows local users to cause a denial of service (OOPS) via crafted keyctl commands.
Commit Message: Merge branch 'keys-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull key handling fixes from David Howells:
 "Here are two patches, the first of which at least should go upstream
  immediately:

  (1) Prevent a user-triggerable crash in the keyrings destructor when a
      negatively instantiated keyring is garbage collected.  I have also
      seen this triggered for user type keys.

  (2) Prevent the user from using requesting that a keyring be created
      and instantiated through an upcall.  Doing so is probably safe
      since the keyring type ignores the arguments to its instantiation
      function - but we probably shouldn't let keyrings be created in
      this manner"

* 'keys-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  KEYS: Don't permit request_key() to construct a new keyring
  KEYS: Fix crash when attempt to garbage collect an uninstantiated keyring