Subject: Re: [PATCH v3 1/3] Send loginuid and sessionid in SCM_AUDIT

From: ebiederm-aS9lmoZGLiVWk0Htik3J/[email-masked] (Eric W. Biederman)
Date: Wed, 04 Sep 2013 00:22:12 -0700

Jan Kaluza <[email-masked]> writes:

> Server-like processes in many cases need credentials and other
> metadata of the peer, to decide if the calling process is allowed to
> request a specific action, or the server just wants to log away this
> type of information for auditing tasks.
>
> The current practice to retrieve such process metadata is to look that
> information up in procfs with the $PID received over SCM_CREDENTIALS.
> This is sufficient for long-running tasks, but introduces a race which
> cannot be worked around for short-living processes; the calling
> process and all the information in /proc/$PID/ is gone before the
> receiver of the socket message can look it up.
>
> This introduces a new SCM type called SCM_AUDIT to allow the direct
> attaching of "loginuid" and "sessionid" to SCM, which is significantly more
> efficient and will reliably avoid the race with the round-trip over
> procfs.

Unless I am misreading something this patch will break the build if
CONFIG_AUDITSYSCALL is not defined.

Eric

> Signed-off-by: Jan Kaluza <[email-masked]>
> ---
>  include/linux/socket.h |  6 ++++++
>  include/net/af_unix.h  |  2 ++
>  include/net/scm.h      | 28 ++++++++++++++++++++++++++--
>  net/unix/af_unix.c     |  7 +++++++
>  4 files changed, 41 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/socket.h b/include/linux/socket.h
> index 445ef75..505047a 100644
> --- a/include/linux/socket.h
> +++ b/include/linux/socket.h
> @@ -130,6 +130,7 @@ static inline struct cmsghdr * cmsg_nxthdr (struct msghdr *__msg, struct cmsghdr
>  #define	SCM_RIGHTS	0x01		/* rw: access rights (array of int) */
>  #define SCM_CREDENTIALS 0x02		/* rw: struct ucred		*/
>  #define SCM_SECURITY	0x03		/* rw: security label		*/
> +#define SCM_AUDIT	0x04		/* rw: struct uaudit		*/
>  
>  struct ucred {
>  	__u32	pid;
> @@ -137,6 +138,11 @@ struct ucred {
>  	__u32	gid;
>  };
>  
> +struct uaudit {
> +	__u32	loginuid;
> +	__u32	sessionid;
> +};
> +
>  /* Supported address families. */
>  #define AF_UNSPEC	0
>  #define AF_UNIX		1	/* Unix domain sockets 		*/
> diff --git a/include/net/af_unix.h b/include/net/af_unix.h
> index a175ba4..3b9d22a 100644
> --- a/include/net/af_unix.h
> +++ b/include/net/af_unix.h
> @@ -36,6 +36,8 @@ struct unix_skb_parms {
>  	u32			secid;		/* Security ID		*/
>  #endif
>  	u32			consumed;
> +	kuid_t			loginuid;
> +	unsigned int		sessionid;
>  };
>  
>  #define UNIXCB(skb) 	(*(struct unix_skb_parms *)&((skb)->cb))
> diff --git a/include/net/scm.h b/include/net/scm.h
> index 8de2d37..e349a25 100644
> --- a/include/net/scm.h
> +++ b/include/net/scm.h
> @@ -6,6 +6,7 @@
>  #include <linux/security.h>
>  #include <linux/pid.h>
>  #include <linux/nsproxy.h>
> +#include <linux/audit.h>
>  
>  /* Well, we should have at least one descriptor open
>   * to accept passed FDs 8)
> @@ -18,6 +19,11 @@ struct scm_creds {
>  	kgid_t	gid;
>  };
>  
> +struct scm_audit {
> +	kuid_t loginuid;
> +	unsigned int sessionid;
> +};
> +
>  struct scm_fp_list {
>  	short			count;
>  	short			max;
> @@ -28,6 +34,7 @@ struct scm_cookie {
>  	struct pid		*pid;		/* Skb credentials */
>  	struct scm_fp_list	*fp;		/* Passed files		*/
>  	struct scm_creds	creds;		/* Skb credentials	*/
> +	struct scm_audit	audit;		/* Skb audit	*/
>  #ifdef CONFIG_SECURITY_NETWORK
>  	u32			secid;		/* Passed security ID 	*/
>  #endif
> @@ -58,6 +65,13 @@ static __inline__ void scm_set_cred(struct scm_cookie *scm,
>  	scm->creds.gid = gid;
>  }
>  
> +static inline void scm_set_audit(struct scm_cookie *scm,
> +				    kuid_t loginuid, unsigned int sessionid)
> +{
> +	scm->audit.loginuid = loginuid;
> +	scm->audit.sessionid = sessionid;
> +}
> +
>  static __inline__ void scm_destroy_cred(struct scm_cookie *scm)
>  {
>  	put_pid(scm->pid);
> @@ -77,8 +91,12 @@ static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
>  	memset(scm, 0, sizeof(*scm));
>  	scm->creds.uid = INVALID_UID;
>  	scm->creds.gid = INVALID_GID;
> -	if (forcecreds)
> -		scm_set_cred(scm, task_tgid(current), current_uid(), current_gid());
> +	if (forcecreds) {
> +		scm_set_cred(scm, task_tgid(current), current_uid(),
> +			     current_gid());
> +		scm_set_audit(scm, audit_get_loginuid(current),
> +			      audit_get_sessionid(current));
> +	}
>  	unix_get_peersec_dgram(sock, scm);
>  	if (msg->msg_controllen <= 0)
>  		return 0;
> @@ -123,7 +141,13 @@ static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
>  			.uid = from_kuid_munged(current_ns, scm->creds.uid),
>  			.gid = from_kgid_munged(current_ns, scm->creds.gid),
>  		};
> +		struct uaudit uaudits = {
> +			.loginuid = from_kuid_munged(current_ns,
> +						     scm->audit.loginuid),
> +			.sessionid = scm->audit.sessionid,
> +		};
>  		put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(ucreds), &ucreds);
> +		put_cmsg(msg, SOL_SOCKET, SCM_AUDIT, sizeof(uaudits), &uaudits);
>  	}
>  
>  	scm_destroy_cred(scm);
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 86de99a..c410f76 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -1393,6 +1393,8 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen
>  	UNIXCB(skb).pid  = get_pid(scm->pid);
>  	UNIXCB(skb).uid = scm->creds.uid;
>  	UNIXCB(skb).gid = scm->creds.gid;
> +	UNIXCB(skb).loginuid = scm->audit.loginuid;
> +	UNIXCB(skb).sessionid = scm->audit.sessionid;
>  	UNIXCB(skb).fp = NULL;
>  	if (scm->fp && send_fds)
>  		err = unix_attach_fds(scm, skb);
> @@ -1416,6 +1418,8 @@ static void maybe_add_creds(struct sk_buff *skb, const struct socket *sock,
>  	    test_bit(SOCK_PASSCRED, &other->sk_socket->flags)) {
>  		UNIXCB(skb).pid  = get_pid(task_tgid(current));
>  		current_uid_gid(&UNIXCB(skb).uid, &UNIXCB(skb).gid);
> +		UNIXCB(skb).loginuid = audit_get_loginuid(current);
> +		UNIXCB(skb).sessionid = audit_get_sessionid(current);
>  	}
>  }
>  
> @@ -1812,6 +1816,7 @@ static int unix_dgram_recvmsg(struct kiocb *iocb, struct socket *sock,
>  		memset(&tmp_scm, 0, sizeof(tmp_scm));
>  	}
>  	scm_set_cred(siocb->scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);
> +	scm_set_audit(siocb->scm, UNIXCB(skb).loginuid, UNIXCB(skb).sessionid);
>  	unix_set_secdata(siocb->scm, skb);
>  
>  	if (!(flags & MSG_PEEK)) {
> @@ -1993,6 +1998,8 @@ again:
>  		} else if (test_bit(SOCK_PASSCRED, &sock->flags)) {
>  			/* Copy credentials */
>  			scm_set_cred(siocb->scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);
> +			scm_set_audit(siocb->scm, UNIXCB(skb).loginuid,
> +				      UNIXCB(skb).sessionid);
>  			check_creds = 1;
>  		}