Prepare fget_unlocked for reading fd table only once.
    
    Some capsicum functions accept fdp + fd and lookup fde based on that.
    Add variants which accept fde.

diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index 96bc585..7abdca0 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -2301,6 +2301,9 @@ int
 fget_unlocked(struct filedesc *fdp, int fd, cap_rights_t *needrightsp,
     int needfcntl, struct file **fpp, cap_rights_t *haverightsp)
 {
+#ifdef CAPABILITIES
+	struct filedescent fde;
+#endif
 	struct file *fp;
 	u_int count;
 #ifdef CAPABILITIES
@@ -2323,17 +2326,22 @@ fget_unlocked(struct filedesc *fdp, int fd, cap_rights_t *needrightsp,
 	 * due to preemption.
 	 */
 	for (;;) {
+#ifdef CAPABILITIES
+		fde = fdp->fd_ofiles[fd];
+		fp = fde.fde_file;
+#else
 		fp = fdp->fd_ofiles[fd].fde_file;
+#endif
 		if (fp == NULL)
 			return (EBADF);
 #ifdef CAPABILITIES
-		haverights = *cap_rights(fdp, fd);
+		haverights = *cap_rights_fde(&fde);
 		if (needrightsp != NULL) {
 			error = cap_check(&haverights, needrightsp);
 			if (error != 0)
 				return (error);
 			if (cap_rights_is_set(needrightsp, CAP_FCNTL)) {
-				error = cap_fcntl_check(fdp, fd, needfcntl);
+				error = cap_fcntl_check_fde(&fde, needfcntl);
 				if (error != 0)
 					return (error);
 			}
diff --git a/sys/kern/sys_capability.c b/sys/kern/sys_capability.c
index e4a42f7..8dd4fbc 100644
--- a/sys/kern/sys_capability.c
+++ b/sys/kern/sys_capability.c
@@ -199,11 +199,19 @@ cap_rights_to_vmprot(cap_rights_t *havep)
  * any other way, as we want to keep all capability permission evaluation in
  * this one file.
  */
+
+cap_rights_t *
+cap_rights_fde(struct filedescent *fde)
+{
+
+	return (&fde->fde_rights);
+}
+
 cap_rights_t *
 cap_rights(struct filedesc *fdp, int fd)
 {
 
-	return (&fdp->fd_ofiles[fd].fde_rights);
+	return (cap_rights_fde(&fdp->fd_ofiles[fd]));
 }
 
 /*
@@ -486,24 +494,28 @@ out:
  * Test whether a capability grants the given fcntl command.
  */
 int
-cap_fcntl_check(struct filedesc *fdp, int fd, int cmd)
+cap_fcntl_check_fde(struct filedescent *fde, int cmd)
 {
 	uint32_t fcntlcap;
 
-	KASSERT(fd >= 0 && fd < fdp->fd_nfiles,
-	    ("%s: invalid fd=%d", __func__, fd));
-
 	fcntlcap = (1 << cmd);
 	KASSERT((CAP_FCNTL_ALL & fcntlcap) != 0,
 	    ("Unsupported fcntl=%d.", cmd));
 
-	if ((fdp->fd_ofiles[fd].fde_fcntls & fcntlcap) != 0)
+	if ((fde->fde_fcntls & fcntlcap) != 0)
 		return (0);
 
 	return (ENOTCAPABLE);
 }
 
 int
+cap_fcntl_check(struct filedesc *fdp, int fd, int cmd)
+{
+
+	return (cap_fcntl_check_fde(&fdp->fd_ofiles[fd], cmd));
+}
+
+int
 sys_cap_fcntls_limit(struct thread *td, struct cap_fcntls_limit_args *uap)
 {
 	struct filedesc *fdp;
diff --git a/sys/sys/capsicum.h b/sys/sys/capsicum.h
index 4942f8d..6188811 100644
--- a/sys/sys/capsicum.h
+++ b/sys/sys/capsicum.h
@@ -341,6 +341,7 @@ __END_DECLS
 #define IN_CAPABILITY_MODE(td) (((td)->td_ucred->cr_flags & CRED_FLAG_CAPMODE) != 0)
 
 struct filedesc;
+struct filedescent;
 
 /*
  * Test whether a capability grants the requested rights.
@@ -355,9 +356,11 @@ u_char	cap_rights_to_vmprot(cap_rights_t *havep);
  * For the purposes of procstat(1) and similar tools, allow kern_descrip.c to
  * extract the rights from a capability.
  */
+cap_rights_t	*cap_rights_fde(struct filedescent *fde);
 cap_rights_t	*cap_rights(struct filedesc *fdp, int fd);
 
 int	cap_ioctl_check(struct filedesc *fdp, int fd, u_long cmd);
+int	cap_fcntl_check_fde(struct filedescent *fde, int cmd);
 int	cap_fcntl_check(struct filedesc *fdp, int fd, int cmd);
 
 #else /* !_KERNEL */