Bring in two sets of changes:

(1) Permit userland applications to request a change of label atomic
    with an execve() via mac_execve().  This is required for the
    SEBSD port of SELinux/FLASK.  Attempts to invoke this without
    MAC compiled in result in ENOSYS, as with all other MAC system
    calls.  Complexity, if desired, is present in policy modules,
    rather than the framework.

(2) Permit policies to have access to both the label of the vnode
    being executed as well as the interpreter if it's a shell
    script or related UNIX nonsense.  Because we can't hold both
    vnode locks at the same time, cache the interpreter label.
    SEBSD relies on this because it supports secure transitioning
    via shell script executables.  Other policies might want to
    take both labels into account during an integrity or
    confidentiality decision at execve()-time.

Approved by:	re
Obtained from:	TrustedBSD Project
Sponsored by:	DARPA, Network Associates Laboratories

1 files changed, 72 insertions, 8 deletions

diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c
index 4586502..d97ed31 100644
--- a/sys/kern/kern_exec.c
+++ b/sys/kern/kern_exec.c
@@ -77,7 +77,7 @@ static MALLOC_DEFINE(M_ATEXEC, "atexec", "atexec callback");
 static int sysctl_kern_ps_strings(SYSCTL_HANDLER_ARGS);
 static int sysctl_kern_usrstack(SYSCTL_HANDLER_ARGS);
 static int kern_execve(struct thread *td, char *fname, char **argv,
-	char **envv);
+	char **envv, struct mac *mac_p);
 
 /*
  * callout list for things to do at exec time
@@ -144,11 +144,12 @@ static const struct execsw **execsw;
  * MPSAFE
  */
 static int
-kern_execve(td, fname, argv, envv)
+kern_execve(td, fname, argv, envv, mac_p)
 	struct thread *td;
 	char *fname;
 	char **argv;
 	char **envv;
+	struct mac *mac_p;
 {
 	struct proc *p = td->td_proc;
 	struct nameidata nd, *ndp;
@@ -168,7 +169,9 @@ kern_execve(td, fname, argv, envv)
 	int credential_changing;
 	int textset;
 #ifdef MAC
-	int will_transition;
+	struct label interplabel;	/* label of the interpreted vnode */
+	struct label execlabel;		/* optional label argument */
+	int will_transition, interplabelvalid = 0;
 #endif
 
 	imgp = &image_params;
@@ -205,6 +208,7 @@ kern_execve(td, fname, argv, envv)
 	imgp->proc = p;
 	imgp->userspace_argv = argv;
 	imgp->userspace_envv = envv;
+	imgp->execlabel = NULL;
 	imgp->attr = &attr;
 	imgp->argc = imgp->envc = 0;
 	imgp->argv0 = NULL;
@@ -219,6 +223,14 @@ kern_execve(td, fname, argv, envv)
 	imgp->ps_strings = 0;
 	imgp->auxarg_size = 0;
 
+#ifdef MAC
+	error = mac_execve_enter(imgp, mac_p, &execlabel);
+	if (error) {
+		mtx_lock(&Giant);
+		goto exec_fail;
+	}
+#endif
+
 	/*
 	 * Allocate temporary demand zeroed space for argument and
 	 *	environment strings
@@ -325,6 +337,11 @@ interpret:
 		imgp->vp->v_vflag &= ~VV_TEXT;
 		/* free name buffer and old vnode */
 		NDFREE(ndp, NDF_ONLY_PNBUF);
+#ifdef MAC
+		mac_init_vnode_label(&interplabel);
+		mac_copy_vnode_label(&ndp->ni_vp->v_label, &interplabel);
+		interplabelvalid = 1;
+#endif
 		vput(ndp->ni_vp);
 		vm_object_deallocate(imgp->object);
 		imgp->object = NULL;
@@ -432,6 +449,9 @@ interpret:
 	 *
 	 * Don't honor setuid/setgid if the filesystem prohibits it or if
 	 * the process is being traced.
+	 *
+	 * XXXMAC: For the time being, use NOSUID to also prohibit
+	 * transitions on the file system.
 	 */
 	oldcred = p->p_ucred;
 	credential_changing = 0;
@@ -440,7 +460,8 @@ interpret:
 	credential_changing |= (attr.va_mode & VSGID) && oldcred->cr_gid !=
 	    attr.va_gid;
 #ifdef MAC
-	will_transition = mac_execve_will_transition(oldcred, imgp->vp);
+	will_transition = mac_execve_will_transition(oldcred, imgp->vp,
+	    interplabelvalid ? &interplabel : NULL, imgp);
 	credential_changing |= will_transition;
 #endif
 
@@ -486,8 +507,10 @@ interpret:
 		if (attr.va_mode & VSGID)
 			change_egid(newcred, attr.va_gid);
 #ifdef MAC
-		if (will_transition)
-			mac_execve_transition(oldcred, newcred, imgp->vp);
+		if (will_transition) {
+			mac_execve_transition(oldcred, newcred, imgp->vp,
+			    interplabelvalid ? &interplabel : NULL, imgp);
+		}
 #endif
 		/*
 		 * Implement correct POSIX saved-id behavior.
@@ -628,11 +651,21 @@ exec_fail:
 	
 	if (imgp->vmspace_destroyed) {
 		/* sorry, no more process anymore. exit gracefully */
+#ifdef MAC
+		mac_execve_exit(imgp);
+		if (interplabelvalid)
+			mac_destroy_vnode_label(&interplabel);
+#endif
 		exit1(td, W_EXITCODE(0, SIGABRT));
 		/* NOT REACHED */
 		error = 0;
 	}
 done2:
+#ifdef MAC
+	mac_execve_exit(imgp);
+	if (interplabelvalid)
+		mac_destroy_vnode_label(&interplabel);
+#endif
 	mtx_unlock(&Giant);
 	return (error);
 }
@@ -658,7 +691,38 @@ execve(td, uap)
 	} */ *uap;
 {
 
-	return (kern_execve(td, uap->fname, uap->argv, uap->envv));
+#ifdef MAC
+	return (kern_execve(td, uap->fname, uap->argv, uap->envv, NULL));
+#else
+	return (ENOSYS);
+#endif
+}
+
+#ifndef _SYS_SYSPROTO_H_
+struct __mac_execve_args {
+	char	*fname;
+	char	**argv;
+	char	**envv;
+	struct mac	*mac_p;
+};
+#endif
+
+/*
+ * MPSAFE
+ */
+int
+__mac_execve(td, uap)
+	struct thread *td;
+	struct __mac_execve_args /* {
+		syscallarg(char *) fname;
+		syscallarg(char **) argv;
+		syscallarg(char **) envv;
+		syscallarg(struct mac *) mac_p;
+	} */ *uap;
+{
+
+	return (kern_execve(td, uap->fname, uap->argv, uap->envv,
+	    uap->mac_p));
 }
 
 int
@@ -1022,7 +1086,7 @@ exec_check_permissions(imgp)
 	td = curthread;			/* XXXKSE */
 
 #ifdef MAC
-	error = mac_check_vnode_exec(td->td_ucred, imgp->vp);
+	error = mac_check_vnode_exec(td->td_ucred, imgp->vp, imgp);
 	if (error)
 		return (error);
 #endif