Limit rights on process descriptors.

On CloudABI, the rights bits returned by cap_rights_get() match up with
the operations that you can actually perform on the file descriptor.

Limiting the rights is good, because it makes it easier to get uniform
behaviour across different operating systems. If process descriptors on
FreeBSD would suddenly gain support for any new file operation, this
wouldn't become exposed to CloudABI processes without first extending
the rights.

Extend fork1() to gain a 'struct filecaps' argument that allows you to
construct process descriptors with custom rights. Use this in
cloudabi_sys_proc_fork() to limit the rights to just fstat() and
pdwait().

Obtained from:	https://github.com/NuxiNL/freebsd

6 files changed, 21 insertions, 14 deletions

diff --git a/sys/compat/cloudabi/cloudabi_proc.c b/sys/compat/cloudabi/cloudabi_proc.c
index 1f4418f..b071aa3 100644
--- a/sys/compat/cloudabi/cloudabi_proc.c
+++ b/sys/compat/cloudabi/cloudabi_proc.c
@@ -27,6 +27,8 @@
 __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
+#include <sys/capsicum.h>
+#include <sys/filedesc.h>
 #include <sys/imgact.h>
 #include <sys/lock.h>
 #include <sys/mutex.h>
@@ -67,10 +69,12 @@ int
 cloudabi_sys_proc_fork(struct thread *td,
     struct cloudabi_sys_proc_fork_args *uap)
 {
+	struct filecaps fcaps = {};
 	struct proc *p2;
 	int error, fd;
 
-	error = fork1(td, RFFDG | RFPROC | RFPROCDESC, 0, &p2, &fd, 0);
+	cap_rights_init(&fcaps.fc_rights, CAP_FSTAT, CAP_PDWAIT);
+	error = fork1(td, RFFDG | RFPROC | RFPROCDESC, 0, &p2, &fd, 0, &fcaps);
 	if (error != 0)
 		return (error);
 	/* Return the file descriptor to the parent process. */
diff --git a/sys/compat/linux/linux_fork.c b/sys/compat/linux/linux_fork.c
index 6b37490..a8bf720 100644
--- a/sys/compat/linux/linux_fork.c
+++ b/sys/compat/linux/linux_fork.c
@@ -73,8 +73,8 @@ linux_fork(struct thread *td, struct linux_fork_args *args)
 		printf(ARGS(fork, ""));
 #endif
 
-	if ((error = fork1(td, RFFDG | RFPROC | RFSTOPPED, 0, &p2, NULL, 0))
-	    != 0)
+	if ((error = fork1(td, RFFDG | RFPROC | RFSTOPPED, 0, &p2, NULL, 0,
+	    NULL)) != 0)
 		return (error);
 
 	td2 = FIRST_THREAD_IN_PROC(p2);
@@ -108,7 +108,7 @@ linux_vfork(struct thread *td, struct linux_vfork_args *args)
 
 	/* Exclude RFPPWAIT */
 	if ((error = fork1(td, RFFDG | RFPROC | RFMEM | RFSTOPPED, 0, &p2,
-	    NULL, 0)) != 0)
+	    NULL, 0, NULL)) != 0)
 		return (error);
 
 
@@ -179,7 +179,7 @@ linux_clone_proc(struct thread *td, struct linux_clone_args *args)
 		if (args->parent_tidptr == NULL)
 			return (EINVAL);
 
-	error = fork1(td, ff, 0, &p2, NULL, 0);
+	error = fork1(td, ff, 0, &p2, NULL, 0, NULL);
 	if (error)
 		return (error);
 
diff --git a/sys/kern/init_main.c b/sys/kern/init_main.c
index a362d00..efb7317 100644
--- a/sys/kern/init_main.c
+++ b/sys/kern/init_main.c
@@ -831,7 +831,7 @@ create_init(const void *udata __unused)
 	int error;
 
 	error = fork1(&thread0, RFFDG | RFPROC | RFSTOPPED, 0, &initproc,
-	    NULL, 0);
+	    NULL, 0, NULL);
 	if (error)
 		panic("cannot fork init: %d\n", error);
 	KASSERT(initproc->p_pid == 1, ("create_init: initproc->p_pid != 1"));
diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index a031435..ccd8792 100644
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -104,7 +104,7 @@ sys_fork(struct thread *td, struct fork_args *uap)
 	int error;
 	struct proc *p2;
 
-	error = fork1(td, RFFDG | RFPROC, 0, &p2, NULL, 0);
+	error = fork1(td, RFFDG | RFPROC, 0, &p2, NULL, 0, NULL);
 	if (error == 0) {
 		td->td_retval[0] = p2->p_pid;
 		td->td_retval[1] = 0;
@@ -127,7 +127,7 @@ sys_pdfork(td, uap)
 	 * itself from the parent using the return value.
 	 */
 	error = fork1(td, RFFDG | RFPROC | RFPROCDESC, 0, &p2,
-	    &fd, uap->flags);
+	    &fd, uap->flags, NULL);
 	if (error == 0) {
 		td->td_retval[0] = p2->p_pid;
 		td->td_retval[1] = 0;
@@ -144,7 +144,7 @@ sys_vfork(struct thread *td, struct vfork_args *uap)
 	struct proc *p2;
 
 	flags = RFFDG | RFPROC | RFPPWAIT | RFMEM;
-	error = fork1(td, flags, 0, &p2, NULL, 0);
+	error = fork1(td, flags, 0, &p2, NULL, 0, NULL);
 	if (error == 0) {
 		td->td_retval[0] = p2->p_pid;
 		td->td_retval[1] = 0;
@@ -163,7 +163,7 @@ sys_rfork(struct thread *td, struct rfork_args *uap)
 		return (EINVAL);
 
 	AUDIT_ARG_FFLAGS(uap->flags);
-	error = fork1(td, uap->flags, 0, &p2, NULL, 0);
+	error = fork1(td, uap->flags, 0, &p2, NULL, 0, NULL);
 	if (error == 0) {
 		td->td_retval[0] = p2 ? p2->p_pid : 0;
 		td->td_retval[1] = 0;
@@ -768,7 +768,7 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
 
 int
 fork1(struct thread *td, int flags, int pages, struct proc **procp,
-    int *procdescp, int pdflags)
+    int *procdescp, int pdflags, struct filecaps *fcaps)
 {
 	struct proc *p1;
 	struct proc *newproc;
@@ -824,7 +824,8 @@ fork1(struct thread *td, int flags, int pages, struct proc **procp,
 	 * later.
 	 */
 	if (flags & RFPROCDESC) {
-		error = falloc(td, &fp_procdesc, procdescp, 0);
+		error = falloc_caps(td, &fp_procdesc, procdescp, 0,
+		fcaps);
 		if (error != 0)
 			return (error);
 	}
diff --git a/sys/kern/kern_kthread.c b/sys/kern/kern_kthread.c
index 68903ba..2072dc7 100644
--- a/sys/kern/kern_kthread.c
+++ b/sys/kern/kern_kthread.c
@@ -89,7 +89,7 @@ kproc_create(void (*func)(void *), void *arg,
 		panic("kproc_create called too soon");
 
 	error = fork1(&thread0, RFMEM | RFFDG | RFPROC | RFSTOPPED | flags,
-	    pages, &p2, NULL, 0);
+	    pages, &p2, NULL, 0, NULL);
 	if (error)
 		return error;
 
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index 40893ed..9689b17 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -161,6 +161,7 @@ struct pargs {
  * for write access.
  */
 struct cpuset;
+struct filecaps;
 struct kaioinfo;
 struct kaudit_record;
 struct kdtrace_proc;
@@ -916,7 +917,8 @@ int	enterpgrp(struct proc *p, pid_t pgid, struct pgrp *pgrp,
 int	enterthispgrp(struct proc *p, struct pgrp *pgrp);
 void	faultin(struct proc *p);
 void	fixjobc(struct proc *p, struct pgrp *pgrp, int entering);
-int	fork1(struct thread *, int, int, struct proc **, int *, int);
+int	fork1(struct thread *, int, int, struct proc **, int *, int,
+	    struct filecaps *);
 void	fork_exit(void (*)(void *, struct trapframe *), void *,
 	    struct trapframe *);
 void	fork_return(struct thread *, struct trapframe *);