Commit message: KEYS: fix keyctl_set_reqkey_keyring() to not leak thread keyrings

This fixes CVE-2017-7472.

Running the following program as an unprivileged user exhausts kernel
memory by leaking thread keyrings:

	#include <keyutils.h>

	int main()
	{
		for (;;)
			keyctl_set_reqkey_keyring(KEY_REQKEY_DEFL_THREAD_KEYRING);
	}

Fix it by only creating a new thread keyring if there wasn't one before.
To make things more consistent, make install_thread_keyring_to_cred()
and install_process_keyring_to_cred() both return 0 if the corresponding
keyring is already present.

Fixes: d84f4f992cbd ("CRED: Inaugurate COW credentials")
Cc: stable@vger.kernel.org # 2.6.29+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
CVE: CVE-2017-7472
CWE: CWE-404
Vulnerability description: The KEYS subsystem in the Linux kernel before 4.10.13 allows local users to cause a denial of service (memory consumption) via a series of KEY_REQKEY_DEFL_THREAD_KEYRING keyctl_set_reqkey_keyring calls.

Project: linux
File: keyctl.c

SYSCALL_DEFINE5(keyctl, int, option, unsigned long, arg2, unsigned long, arg3,
		unsigned long, arg4, unsigned long, arg5)
{
	switch (option) {
	case KEYCTL_GET_KEYRING_ID:
		return keyctl_get_keyring_ID((key_serial_t) arg2,
					     (int) arg3);

	case KEYCTL_JOIN_SESSION_KEYRING:
		return keyctl_join_session_keyring((const char __user *) arg2);

	case KEYCTL_UPDATE:
		return keyctl_update_key((key_serial_t) arg2,
					 (const void __user *) arg3,
					 (size_t) arg4);

	case KEYCTL_REVOKE:
		return keyctl_revoke_key((key_serial_t) arg2);

	case KEYCTL_DESCRIBE:
		return keyctl_describe_key((key_serial_t) arg2,
					   (char __user *) arg3,
					   (unsigned) arg4);

	case KEYCTL_CLEAR:
		return keyctl_keyring_clear((key_serial_t) arg2);

	case KEYCTL_LINK:
		return keyctl_keyring_link((key_serial_t) arg2,
					   (key_serial_t) arg3);

	case KEYCTL_UNLINK:
		return keyctl_keyring_unlink((key_serial_t) arg2,
					     (key_serial_t) arg3);

	case KEYCTL_SEARCH:
		return keyctl_keyring_search((key_serial_t) arg2,
					     (const char __user *) arg3,
					     (const char __user *) arg4,
					     (key_serial_t) arg5);

	case KEYCTL_READ:
		return keyctl_read_key((key_serial_t) arg2,
				       (char __user *) arg3,
				       (size_t) arg4);

	case KEYCTL_CHOWN:
		return keyctl_chown_key((key_serial_t) arg2,
					(uid_t) arg3,
					(gid_t) arg4);

	case KEYCTL_SETPERM:
		return keyctl_setperm_key((key_serial_t) arg2,
					  (key_perm_t) arg3);

	case KEYCTL_INSTANTIATE:
		return keyctl_instantiate_key((key_serial_t) arg2,
					      (const void __user *) arg3,
					      (size_t) arg4,
					      (key_serial_t) arg5);

	case KEYCTL_NEGATE:
		return keyctl_negate_key((key_serial_t) arg2,
					 (unsigned) arg3,
					 (key_serial_t) arg4);

	case KEYCTL_SET_REQKEY_KEYRING:
		return keyctl_set_reqkey_keyring(arg2);

	case KEYCTL_SET_TIMEOUT:
		return keyctl_set_timeout((key_serial_t) arg2,
					  (unsigned) arg3);

	case KEYCTL_ASSUME_AUTHORITY:
		return keyctl_assume_authority((key_serial_t) arg2);

	case KEYCTL_GET_SECURITY:
		return keyctl_get_security((key_serial_t) arg2,
					   (char __user *) arg3,
					   (size_t) arg4);

	case KEYCTL_SESSION_TO_PARENT:
		return keyctl_session_to_parent();

	case KEYCTL_REJECT:
		return keyctl_reject_key((key_serial_t) arg2,
					 (unsigned) arg3,
					 (unsigned) arg4,
					 (key_serial_t) arg5);

	case KEYCTL_INSTANTIATE_IOV:
		return keyctl_instantiate_key_iov(
			(key_serial_t) arg2,
			(const struct iovec __user *) arg3,
			(unsigned) arg4,
			(key_serial_t) arg5);

	case KEYCTL_INVALIDATE:
		return keyctl_invalidate_key((key_serial_t) arg2);

	case KEYCTL_GET_PERSISTENT:
		return keyctl_get_persistent((uid_t)arg2, (key_serial_t)arg3);

	case KEYCTL_DH_COMPUTE:
		return keyctl_dh_compute((struct keyctl_dh_params __user *) arg2,
					 (char __user *) arg3, (size_t) arg4,
					 (void __user *) arg5);

	default:
		return -EOPNOTSUPP;
	}
}

Project: linux
File: keyctl.c

long keyctl_instantiate_key_common(key_serial_t id,
				   struct iov_iter *from,
				   key_serial_t ringid)
{
	const struct cred *cred = current_cred();
	struct request_key_auth *rka;
	struct key *instkey, *dest_keyring;
	size_t plen = from ? iov_iter_count(from) : 0;
	void *payload;
	long ret;

	kenter("%d,,%zu,%d", id, plen, ringid);

	if (!plen)
		from = NULL;

	ret = -EINVAL;
	if (plen > 1024 * 1024 - 1)
		goto error;

	/* the appropriate instantiation authorisation key must have been
	 * assumed before calling this */
	ret = -EPERM;
	instkey = cred->request_key_auth;
	if (!instkey)
		goto error;

	rka = instkey->payload.data[0];
	if (rka->target_key->serial != id)
		goto error;

	/* pull the payload in if one was supplied */
	payload = NULL;

	if (from) {
		ret = -ENOMEM;
		payload = kmalloc(plen, GFP_KERNEL);
		if (!payload) {
			if (plen <= PAGE_SIZE)
				goto error;
			payload = vmalloc(plen);
			if (!payload)
				goto error;
		}

		ret = -EFAULT;
		if (!copy_from_iter_full(payload, plen, from))
			goto error2;
	}

	/* find the destination keyring amongst those belonging to the
	 * requesting task */
	ret = get_instantiation_keyring(ringid, rka, &dest_keyring);
	if (ret < 0)
		goto error2;

	/* instantiate the key and link it into a keyring */
	ret = key_instantiate_and_link(rka->target_key, payload, plen,
				       dest_keyring, instkey);

	key_put(dest_keyring);

	/* discard the assumed authority if it's just been disabled by
	 * instantiation of the key */
	if (ret == 0)
		keyctl_change_reqkey_auth(NULL);

error2:
	kvfree(payload);
error:
	return ret;
}

Project: linux
File: process_keys.c

long join_session_keyring(const char *name)
{
	const struct cred *old;
	struct cred *new;
	struct key *keyring;
	long ret, serial;

	new = prepare_creds();
	if (!new)
		return -ENOMEM;
	old = current_cred();

	/* if no name is provided, install an anonymous keyring */
	if (!name) {
		ret = install_session_keyring_to_cred(new, NULL);
		if (ret < 0)
			goto error;

		serial = new->session_keyring->serial;
		ret = commit_creds(new);
		if (ret == 0)
			ret = serial;
		goto okay;
	}

	/* allow the user to join or create a named keyring */
	mutex_lock(&key_session_mutex);

	/* look for an existing keyring of this name */
	keyring = find_keyring_by_name(name, false);
	if (PTR_ERR(keyring) == -ENOKEY) {
		/* not found - try and create a new one */
		keyring = keyring_alloc(
			name, old->uid, old->gid, old,
			KEY_POS_ALL | KEY_USR_VIEW | KEY_USR_READ | KEY_USR_LINK,
			KEY_ALLOC_IN_QUOTA, NULL, NULL);
		if (IS_ERR(keyring)) {
			ret = PTR_ERR(keyring);
			goto error2;
		}
	} else if (IS_ERR(keyring)) {
		ret = PTR_ERR(keyring);
		goto error2;
	} else if (keyring == new->session_keyring) {
		key_put(keyring);
		ret = 0;
		goto error2;
	}

	/* we've got a keyring - now to install it */
	ret = install_session_keyring_to_cred(new, keyring);
	if (ret < 0)
		goto error2;

	commit_creds(new);
	mutex_unlock(&key_session_mutex);

	ret = keyring->serial;
	key_put(keyring);
okay:
	return ret;

error2:
	mutex_unlock(&key_session_mutex);
error:
	abort_creds(new);
	return ret;
}