Commit message: net: fix incorrect credentials passing

Commit 257b5358b32f ("scm: Capture the full credentials of the scm
sender") changed the credentials passing code to pass in the effective
uid/gid instead of the real uid/gid.

Obviously this doesn't matter most of the time (since normally they are
the same), but it results in differences for suid binaries when the wrong
uid/gid ends up being used.

This just undoes that (presumably unintentional) part of the commit.

Reported-by: Andy Lutomirski <luto@amacapital.net>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Serge E. Hallyn <serge@hallyn.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
CVE: CVE-2013-1979
CWE: CWE-284
Vulnerability description: The scm_set_cred function in include/net/scm.h in the Linux kernel before 3.8.11 uses incorrect uid and gid values during credentials passing, which allows local users to gain privileges via a crafted application.

Project: linux
File: scm.h

static __inline__ void scm_destroy_cred(struct scm_cookie *scm)
{
	put_pid(scm->pid);
	scm->pid  = NULL;

	if (scm->cred)
		put_cred(scm->cred);
	scm->cred = NULL;
}

Project: linux
File: scm.h

static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_cookie *scm)
{ }

Project: linux
File: scm.h

static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
{ }

Project: linux
File: scm.h

static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
				struct scm_cookie *scm, int flags)
{
	if (!msg->msg_control) {
		if (test_bit(SOCK_PASSCRED, &sock->flags) || scm->fp)
			msg->msg_flags |= MSG_CTRUNC;
		scm_destroy(scm);
		return;
	}

	if (test_bit(SOCK_PASSCRED, &sock->flags)) {
		struct user_namespace *current_ns = current_user_ns();
		struct ucred ucreds = {
			.pid = scm->creds.pid,
			.uid = from_kuid_munged(current_ns, scm->creds.uid),
			.gid = from_kgid_munged(current_ns, scm->creds.gid),
		};
		put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(ucreds), &ucreds);
	}

	scm_destroy_cred(scm);

	scm_passec(sock, msg, scm);

	if (!scm->fp)
		return;
	
	scm_detach_fds(msg, scm);
}

Project: linux
File: scm.h

static __inline__ void scm_set_cred(struct scm_cookie *scm,
				    struct pid *pid, const struct cred *cred)
{
	scm->pid  = get_pid(pid);
	scm->cred = cred ? get_cred(cred) : NULL;
	scm->creds.pid = pid_vnr(pid);
	scm->creds.uid = cred ? cred->uid : INVALID_UID;
	scm->creds.gid = cred ? cred->gid : INVALID_GID;
}

Project: linux
File: scm.h

static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_cookie *scm)
{
	security_socket_getpeersec_dgram(sock, NULL, &scm->secid);
}

Project: linux
File: scm.h

static __inline__ void scm_destroy(struct scm_cookie *scm)
{
	scm_destroy_cred(scm);
	if (scm->fp)
		__scm_destroy(scm);
}

Project: linux
File: scm.h

static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
{
	char *secdata;
	u32 seclen;
	int err;

	if (test_bit(SOCK_PASSSEC, &sock->flags)) {
		err = security_secid_to_secctx(scm->secid, &secdata, &seclen);

		if (!err) {
			put_cmsg(msg, SOL_SOCKET, SCM_SECURITY, seclen, secdata);
			security_release_secctx(secdata, seclen);
		}
	}
}

Project: linux
File: scm.h

static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
			       struct scm_cookie *scm, bool forcecreds)
{
	memset(scm, 0, sizeof(*scm));
	if (forcecreds)
		scm_set_cred(scm, task_tgid(current), current_cred());
	unix_get_peersec_dgram(sock, scm);
	if (msg->msg_controllen <= 0)
		return 0;
	return __scm_send(sock, msg, scm);
}