file: Add a helper function to check whether filecaps are full

In a couple of places we want to know whether someone has limited rights
on an fd.  There, we want a predicate which determines whether the set
of rights is smaller than CAP_ALL, and whether there are explicit ioctl
or fcntl lists.  Factor this out into a helper function, in preparation
for use elsewhere.

No functional change intended.

Approved by:	so
Security:	FreeBSD-SA-26:66.jail
Reviewed by:	kib
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D59884

sys/kern/kern_descrip.c

@@ -1844,6 +1844,16 @@ filecaps_free(struct filecaps *fcaps)
 	bzero(fcaps, sizeof(*fcaps));
 }
 
+bool
+filecaps_full(const struct filecaps *fcaps)
+{
+	cap_rights_t allrights;
+
+	CAP_ALL(&allrights);
+	return (cap_rights_contains(&fcaps->fc_rights, &allrights) &&
+	    fcaps->fc_fcntls == CAP_FCNTL_ALL && fcaps->fc_nioctls == -1);
+}
+
 static u_long *
 filecaps_free_prep(struct filecaps *fcaps)
 {
@@ -3113,10 +3123,7 @@ fgetvp_lookup_smr(struct nameidata *ndp, struct vnode **vpp, int *flagsp)
 	 *
 	 * Not yet supported by fast path.
 	 */
-	CAP_ALL(&rights);
-	if (!cap_rights_contains(&ndp->ni_filecaps.fc_rights, &rights) ||
-	    ndp->ni_filecaps.fc_fcntls != CAP_FCNTL_ALL ||
-	    ndp->ni_filecaps.fc_nioctls != -1) {
+	if (!filecaps_full(&ndp->ni_filecaps)) {
 #ifdef notyet
 		ndp->ni_lcf |= NI_LCF_STRICTREL;
 #else
@@ -3218,10 +3225,7 @@ fgetvp_lookup(struct nameidata *ndp, struct vnode **vpp)
 	 * all lookups relative to it must also be
 	 * strictly relative.
 	 */
-	CAP_ALL(&rights);
-	if (!cap_rights_contains(&ndp->ni_filecaps.fc_rights, &rights) ||
-	    ndp->ni_filecaps.fc_fcntls != CAP_FCNTL_ALL ||
-	    ndp->ni_filecaps.fc_nioctls != -1) {
+	if (!filecaps_full(&ndp->ni_filecaps)) {
 		ndp->ni_lcf |= NI_LCF_STRICTREL;
 		ndp->ni_resflags |= NIRES_STRICTREL;
 	}

sys/sys/filedesc.h

@@ -244,6 +244,7 @@ bool	filecaps_copy(const struct filecaps *src, struct filecaps *dst,
 	    bool locked);
 void	filecaps_move(struct filecaps *src, struct filecaps *dst);
 void	filecaps_free(struct filecaps *fcaps);
+bool	filecaps_full(const struct filecaps *fcaps);
 
 int	closef(struct file *fp, struct thread *td);
 void	closef_nothread(struct file *fp);