Code:  long keyctl_set_reqkey_keyring(int reqkey_defl)
 {
	struct cred *new;
	int ret, old_setting;

	old_setting = current_cred_xxx(jit_keyring);

	if (reqkey_defl == KEY_REQKEY_DEFL_NO_CHANGE)
		return old_setting;

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

	switch (reqkey_defl) {
	case KEY_REQKEY_DEFL_THREAD_KEYRING:
		ret = install_thread_keyring_to_cred(new);
		if (ret < 0)
			goto error;
		goto set;
 
 	case KEY_REQKEY_DEFL_PROCESS_KEYRING:
 		ret = install_process_keyring_to_cred(new);
		if (ret < 0) {
			if (ret != -EEXIST)
				goto error;
			ret = 0;
		}
 		goto set;
 
 	case KEY_REQKEY_DEFL_DEFAULT:
	case KEY_REQKEY_DEFL_SESSION_KEYRING:
	case KEY_REQKEY_DEFL_USER_KEYRING:
	case KEY_REQKEY_DEFL_USER_SESSION_KEYRING:
	case KEY_REQKEY_DEFL_REQUESTOR_KEYRING:
		goto set;

	case KEY_REQKEY_DEFL_NO_CHANGE:
	case KEY_REQKEY_DEFL_GROUP_KEYRING:
	default:
		ret = -EINVAL;
		goto error;
	}

set:
	new->jit_keyring = reqkey_defl;
	commit_creds(new);
	return old_setting;
error:
	abort_creds(new);
	return ret;
}

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>
CWE ID: CWE-404
 long keyctl_set_reqkey_keyring(int reqkey_defl)
 {
	struct cred *new;
	int ret, old_setting;

	old_setting = current_cred_xxx(jit_keyring);

	if (reqkey_defl == KEY_REQKEY_DEFL_NO_CHANGE)
		return old_setting;

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

	switch (reqkey_defl) {
	case KEY_REQKEY_DEFL_THREAD_KEYRING:
		ret = install_thread_keyring_to_cred(new);
		if (ret < 0)
			goto error;
		goto set;
 
 	case KEY_REQKEY_DEFL_PROCESS_KEYRING:
 		ret = install_process_keyring_to_cred(new);
		if (ret < 0)
			goto error;
 		goto set;
 
 	case KEY_REQKEY_DEFL_DEFAULT:
	case KEY_REQKEY_DEFL_SESSION_KEYRING:
	case KEY_REQKEY_DEFL_USER_KEYRING:
	case KEY_REQKEY_DEFL_USER_SESSION_KEYRING:
	case KEY_REQKEY_DEFL_REQUESTOR_KEYRING:
		goto set;

	case KEY_REQKEY_DEFL_NO_CHANGE:
	case KEY_REQKEY_DEFL_GROUP_KEYRING:
	default:
		ret = -EINVAL;
		goto error;
	}

set:
	new->jit_keyring = reqkey_defl;
	commit_creds(new);
	return old_setting;
error:
	abort_creds(new);
	return ret;
}
