[PATCH v2 3/3] Send cgroup_path in SCM_CGROUP

[Jan Kaluza <jkaluza-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

Add new SCM type called SCM_CGROUP to send "cgroup_path" in SCM.
This is useful for journald (systemd logging daemon) to get additional context
with each log line received using UNIX socket.

Signed-off-by: Jan Kaluza <jkaluza-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 include/linux/socket.h |  1 +
 include/net/af_unix.h  |  1 +
 include/net/scm.h      | 15 +++++++++++++++
 net/core/scm.c         | 18 ++++++++++++++++++
 net/unix/af_unix.c     | 20 ++++++++++++++++++++
 5 files changed, 55 insertions(+)

diff --git a/include/linux/socket.h b/include/linux/socket.h
index 6c7ace0..621fff1 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -133,6 +133,7 @@ static inline struct cmsghdr * cmsg_nxthdr (struct msghdr *__msg, struct cmsghdr
 #define SCM_AUDIT	0x04		/* rw: struct uaudit		*/
 #define SCM_PROCINFO	0x05	/* rw: comm + cmdline (NULL terminated
 					   array of char *) */
+#define SCM_CGROUP	0x06		/* rw: cgroup path */
 
 struct ucred {
 	__u32	pid;
diff --git a/include/net/af_unix.h b/include/net/af_unix.h
index 05c7678..c49bf35 100644
--- a/include/net/af_unix.h
+++ b/include/net/af_unix.h
@@ -32,6 +32,7 @@ struct unix_skb_parms_scm {
 	unsigned int sessionid;
 	char *procinfo;
 	int procinfo_len;
+	char *cgroup_path;
 };
 
 struct unix_skb_parms {
diff --git a/include/net/scm.h b/include/net/scm.h
index 3346030..5398826 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -41,6 +41,7 @@ struct scm_cookie {
 	struct scm_creds	creds;		/* Skb credentials	*/
 	struct scm_audit	audit;		/* Skb audit	*/
 	struct scm_procinfo	procinfo;	/* Skb procinfo */
+	char *cgroup_path;
 #ifdef CONFIG_SECURITY_NETWORK
 	u32			secid;		/* Passed security ID 	*/
 #endif
@@ -52,6 +53,7 @@ extern int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie
 extern void __scm_destroy(struct scm_cookie *scm);
 extern struct scm_fp_list * scm_fp_dup(struct scm_fp_list *fpl);
 extern int scm_get_current_procinfo(char **procinfo);
+extern int scm_get_current_cgroup_path(char **cgroup_path);
 
 #ifdef CONFIG_SECURITY_NETWORK
 static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_cookie *scm)
@@ -86,6 +88,12 @@ static inline void scm_set_procinfo(struct scm_cookie *scm,
 	scm->procinfo.len = len;
 }
 
+static inline void scm_set_cgroup_path(struct scm_cookie *scm,
+				    char *cgroup_path)
+{
+	scm->cgroup_path = cgroup_path;
+}
+
 static __inline__ void scm_destroy_cred(struct scm_cookie *scm)
 {
 	put_pid(scm->pid);
@@ -140,6 +148,9 @@ static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct sc
 			security_release_secctx(secdata, seclen);
 		}
 	}
+
+	kfree(scm->cgroup_path);
+	scm->cgroup_path = NULL;
 }
 #else
 static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
@@ -172,6 +183,10 @@ static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
 		put_cmsg(msg, SOL_SOCKET, SCM_AUDIT, sizeof(uaudits), &uaudits);
 		put_cmsg(msg, SOL_SOCKET, SCM_PROCINFO, scm->procinfo.len,
 				 scm->procinfo.procinfo);
+		if (scm->cgroup_path) {
+			put_cmsg(msg, SOL_SOCKET, SCM_CGROUP,
+				 strlen(scm->cgroup_path), scm->cgroup_path);
+		}
 	}
 
 	scm_destroy_cred(scm);
diff --git a/net/core/scm.c b/net/core/scm.c
index 09ec044..2d408b9 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -404,3 +404,21 @@ out:
 	return res;
 }
 EXPORT_SYMBOL(scm_get_current_procinfo);
+
+int scm_get_current_cgroup_path(char **cgroup_path)
+{
+	int ret = 0;
+
+	*cgroup_path = kmalloc(PATH_MAX, GFP_KERNEL);
+	if (!(*cgroup_path))
+		return -ENOMEM;
+
+	ret = task_cgroup_path(current, *cgroup_path, PATH_MAX);
+	if (ret < 0) {
+		kfree(*cgroup_path);
+		*cgroup_path = NULL;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(scm_get_current_cgroup_path);
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index ab0be13..b638083 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1344,6 +1344,7 @@ static void unix_destruct_scm(struct sk_buff *skb)
 	if (UNIXCB(skb).scm) {
 		scm.procinfo.procinfo = UNIXSCM(skb).procinfo;
 		scm.procinfo.len = UNIXSCM(skb).procinfo_len;
+		scm.cgroup_path = UNIXSCM(skb).cgroup_path;
 	}
 	if (UNIXCB(skb).fp)
 		unix_detach_fds(&scm, skb);
@@ -1420,6 +1421,14 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen
 			return -ENOMEM;
 	}
 
+	UNIXSCM(skb).cgroup_path = NULL;
+	if (scm->cgroup_path) {
+		UNIXSCM(skb).cgroup_path = kstrdup(scm->cgroup_path,
+						   GFP_KERNEL);
+		if (!UNIXSCM(skb).cgroup_path)
+			return -ENOMEM;
+	}
+
 	skb->destructor = unix_destruct_scm;
 	return err;
 }
@@ -1443,6 +1452,7 @@ static void maybe_add_creds(struct sk_buff *skb, const struct socket *sock,
 		UNIXSCM(skb).sessionid = audit_get_sessionid(current);
 		UNIXSCM(skb).procinfo_len = scm_get_current_procinfo(
 			&UNIXSCM(skb).procinfo);
+		scm_get_current_cgroup_path(&UNIXSCM(skb).cgroup_path);
 	}
 }
 
@@ -1849,6 +1859,11 @@ static int unix_dgram_recvmsg(struct kiocb *iocb, struct socket *sock,
 						 GFP_KERNEL),
 					 UNIXSCM(skb).procinfo_len);
 		}
+		if (UNIXSCM(skb).cgroup_path) {
+			scm_set_cgroup_path(siocb->scm,
+					    kstrdup(UNIXSCM(skb).cgroup_path,
+						    GFP_KERNEL));
+		}
 	}
 	unix_set_secdata(siocb->scm, skb);
 
@@ -2042,6 +2057,11 @@ again:
 						GFP_KERNEL),
 						UNIXSCM(skb).procinfo_len);
 				}
+				if (UNIXSCM(skb).cgroup_path) {
+					scm_set_cgroup_path(siocb->scm,
+							    kstrdup(UNIXSCM(skb).cgroup_path,
+							    GFP_KERNEL));
+				}
 			}
 			check_creds = 1;
 		}
-- 
1.8.3.1