[PATCH v15 22/23] LSM: Add /proc attr entry for full LSM context

@@ -199,3 +199,25 @@ capability-related fields:
 -  ``fs/nfsd/auth.c``::c:func:`nfsd_setuser()`
 
 -  ``fs/proc/array.c``::c:func:`task_cap()`
+
+LSM External Interfaces
+=======================
+
+The LSM infrastructure does not generally provide external interfaces.
+The individual security modules provide what external interfaces they
+require.
+
+The infrastructure does provide an interface for the special
+case where multiple security modules provide a process context.
+This is provided in compound context format.
+
+-  `lsm1\0value\0lsm2\0value\0`
+
+The `value` is a nul terminated bytestring. It may contain
+whitespace or non-printable characters. 
+
+The special file ``/proc/pid/attr/context`` provides the security
+context of the identified process.
+
+The special file ``/sys/kernel/security/lsm`` provides a comma
+separated list of the active security modules.

@@ -2744,6 +2744,7 @@ static const struct pid_entry attr_dir_stuff[] = {
 	ATTR(NULL, "keycreate",		0666),
 	ATTR(NULL, "sockcreate",	0666),
 	ATTR(NULL, "display",		0666),
+	ATTR(NULL, "context",		0444),
 #ifdef CONFIG_SECURITY_SMACK
 	DIR("smack",			0555,
 	    proc_smack_attr_dir_inode_ops, proc_smack_attr_dir_ops),

@@ -1321,6 +1321,12 @@
  *	@pages contains the number of pages.
  *	Return 0 if permission is granted.
  *
+ * @getprocattr:
+ *	Provide the named process attribute for display in special files in
+ *	the /proc/.../attr directory.  Attribute naming and the data displayed
+ *	is at the discretion of the security modules.  The exception is the
+ *	"context" attribute, which will contain the security context of the
+ *	task as a nul terminated text string without trailing whitespace.
  * @ismaclabel:
  *	Check if the extended attribute specified by @name
  *	represents a MAC label. Returns 1 if name is a MAC

@@ -11,7 +11,7 @@
 #ifndef __AA_PROCATTR_H
 #define __AA_PROCATTR_H
 
-int aa_getprocattr(struct aa_label *label, char **string);
+int aa_getprocattr(struct aa_label *label, char **string, bool newline);
 int aa_setprocattr_changehat(char *args, size_t size, int flags);
 
 #endif /* __AA_PROCATTR_H */

@@ -593,6 +593,7 @@ static int apparmor_getprocattr(struct task_struct *task, char *name,
 	const struct cred *cred = get_task_cred(task);
 	struct aa_task_ctx *ctx = task_ctx(current);
 	struct aa_label *label = NULL;
+	bool newline = true;
 
 	if (strcmp(name, "current") == 0)
 		label = aa_get_newest_label(cred_label(cred));

@@ -600,11 +601,14 @@ static int apparmor_getprocattr(struct task_struct *task, char *name,
 		label = aa_get_newest_label(ctx->previous);
 	else if (strcmp(name, "exec") == 0 && ctx->onexec)
 		label = aa_get_newest_label(ctx->onexec);
-	else
+	else if (strcmp(name, "context") == 0) {
+		label = aa_get_newest_label(cred_label(cred));
+		newline = false;
+	} else
 		error = -EINVAL;
 
 	if (label)
-		error = aa_getprocattr(label, value);
+		error = aa_getprocattr(label, value, newline);
 
 	aa_put_label(label);
 	put_cred(cred);

@@ -20,6 +20,7 @@
  * aa_getprocattr - Return the profile information for @profile
  * @profile: the profile to print profile info about  (NOT NULL)
  * @string: Returns - string containing the profile info (NOT NULL)
+ * @newline: Should a newline be added to @string.
  *
  * Returns: length of @string on success else error on failure
  *

@@ -30,20 +31,21 @@
  *
  * Returns: size of string placed in @string else error code on failure
  */
-int aa_getprocattr(struct aa_label *label, char **string)
+int aa_getprocattr(struct aa_label *label, char **string, bool newline)
 {
 	struct aa_ns *ns = labels_ns(label);
 	struct aa_ns *current_ns = aa_get_current_ns();
+	int flags = FLAG_VIEW_SUBNS | FLAG_HIDDEN_UNCONFINED;
 	int len;
 
 	if (!aa_ns_visible(current_ns, ns, true)) {
 		aa_put_ns(current_ns);
 		return -EACCES;
 	}
+	if (newline)
+		flags |= FLAG_SHOW_MODE;
 
-	len = aa_label_snxprint(NULL, 0, current_ns, label,
-				FLAG_SHOW_MODE | FLAG_VIEW_SUBNS |
-				FLAG_HIDDEN_UNCONFINED);
+	len = aa_label_snxprint(NULL, 0, current_ns, label, flags);
 	AA_BUG(len < 0);
 
 	*string = kmalloc(len + 2, GFP_KERNEL);

@@ -52,19 +54,19 @@ int aa_getprocattr(struct aa_label *label, char **string)
 		return -ENOMEM;
 	}
 
-	len = aa_label_snxprint(*string, len + 2, current_ns, label,
-				FLAG_SHOW_MODE | FLAG_VIEW_SUBNS |
-				FLAG_HIDDEN_UNCONFINED);
+	len = aa_label_snxprint(*string, len + 2, current_ns, label, flags);
 	if (len < 0) {
 		aa_put_ns(current_ns);
 		return len;
 	}
 
-	(*string)[len] = '\n';
-	(*string)[len + 1] = 0;
+	if (newline) {
+		(*string)[len] = '\n';
+		(*string)[++len] = 0;
+	}
 
 	aa_put_ns(current_ns);
-	return len + 1;
+	return len;
 }
 
 /**

@@ -754,6 +754,42 @@ static void __init lsm_early_task(struct task_struct *task)
 		panic("%s: Early task alloc failed.\n", __func__);
 }
 
+/**
+ * append_ctx - append a lsm/context pair to a compound context
+ * @ctx: the existing compound context
+ * @ctxlen: size of the old context, including terminating nul byte
+ * @lsm: new lsm name, nul terminated
+ * @new: new context, possibly nul terminated
+ * @newlen: maximum size of @new
+ *
+ * replace @ctx with a new compound context, appending @newlsm and @new
+ * to @ctx. On exit the new data replaces the old, which is freed.
+ * @ctxlen is set to the new size, which includes a trailing nul byte.
+ *
+ * Returns 0 on success, -ENOMEM if no memory is available.
+ */
+static int append_ctx(char **ctx, int *ctxlen, const char *lsm, char *new,
+		      int newlen)
+{
+	char *final;
+	int llen;
+
+	llen = strlen(lsm) + 1;
+	newlen = strnlen(new, newlen) + 1;
+
+	final = kzalloc(*ctxlen + llen + newlen, GFP_KERNEL);
+	if (final == NULL)
+		return -ENOMEM;
+	if (*ctxlen)
+		memcpy(final, *ctx, *ctxlen);
+	memcpy(final + *ctxlen, lsm, llen);
+	memcpy(final + *ctxlen + llen, new, newlen);
+	kfree(*ctx);
+	*ctx = final;
+	*ctxlen = *ctxlen + llen + newlen;
+	return 0;
+}
+
 /*
  * Hook list operation macros.
  *

@@ -2073,6 +2109,10 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name,
 				char **value)
 {
 	struct security_hook_list *hp;
+	char *final = NULL;
+	char *cp;
+	int rc = 0;
+	int finallen = 0;
 	int display = lsm_task_display(current);
 	int slot = 0;
 

@@ -2100,6 +2140,29 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name,
 		return -ENOMEM;
 	}
 
+	if (!strcmp(name, "context")) {
+		hlist_for_each_entry(hp, &security_hook_heads.getprocattr,
+				     list) {
+			rc = hp->hook.getprocattr(p, "context", &cp);
+			if (rc == -EINVAL || rc == -ENOPROTOOPT)
+				continue;
+			if (rc < 0) {
+				kfree(final);
+				return rc;
+			}
+			rc = append_ctx(&final, &finallen, hp->lsmid->lsm,
+					cp, rc);
+			if (rc < 0) {
+				kfree(final);
+				return rc;
+			}
+		}
+		if (final == NULL)
+			return -EINVAL;
+		*value = final;
+		return finallen;
+	}
+
 	hlist_for_each_entry(hp, &security_hook_heads.getprocattr, list) {
 		if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm))
 			continue;

@@ -6257,7 +6257,7 @@ static int selinux_getprocattr(struct task_struct *p,
 			goto bad;
 	}
 
-	if (!strcmp(name, "current"))
+	if (!strcmp(name, "current") || !strcmp(name, "context"))
 		sid = __tsec->sid;
 	else if (!strcmp(name, "prev"))
 		sid = __tsec->osid;

@@ -3479,7 +3479,7 @@ static int smack_getprocattr(struct task_struct *p, char *name, char **value)
 	char *cp;
 	int slen;
 
-	if (strcmp(name, "current") != 0)
+	if (strcmp(name, "current") != 0 && strcmp(name, "context") != 0)
 		return -EINVAL;
 
 	cp = kstrdup(skp->smk_known, GFP_KERNEL);