On 14/01/13, Jan Kaluza wrote:
> 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.
>
> Signed-off-by: Jan Kaluza <jkaluza@xxxxxxxxxx>
Acked-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
> ---
> 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 5d488a6..eeac565 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 262532d..67de64f 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 800ca61..bc02a25 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -1413,6 +1413,8 @@ 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);
> @@ -1436,6 +1438,8 @@ 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);
> }
> }
>
> @@ -1829,6 +1833,7 @@ 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)) {
> @@ -2008,6 +2013,8 @@ 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;
> }
>
> --
> 1.8.3.1
>
- RGB
--
Richard Guy Briggs <rbriggs@xxxxxxxxxx>
Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat
Remote, Ottawa, Canada
Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545
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