--- sys/kern/kern_cpuset.c	(revision 322327)
+++ sys/kern/kern_cpuset.c	(working copy)
@@ -1097,7 +1097,7 @@ 
 	int error;
 	size_t size;
 
-	if (cpusetsize < sizeof(cpuset_t) || cpusetsize > CPU_MAXSIZE / NBBY)
+	if (cpusetsize < (mp_maxid + NBBY - 1) / NBBY || cpusetsize > CPU_MAXSIZE / NBBY)
 		return (ERANGE);
 	/* In Capability mode, you can only get your own CPU set. */
 	if (IN_CAPABILITY_MODE(td)) {
@@ -1109,7 +1109,7 @@ 
 		return (ECAPMODE);
 	}
 	size = cpusetsize;
-	mask = malloc(size, M_TEMP, M_WAITOK | M_ZERO);
+	mask = malloc(size >= sizeof(cpuset_t) ? size : sizeof(cpuset_t), M_TEMP, M_WAITOK | M_ZERO);
 	error = cpuset_which(which, id, &p, &ttd, &set);
 	if (error)
 		goto out;
@@ -1210,7 +1210,7 @@ 
 	cpuset_t *mask;
 	int error;
 
-	if (cpusetsize < sizeof(cpuset_t) || cpusetsize > CPU_MAXSIZE / NBBY)
+	if (cpusetsize < (mp_maxid + NBBY - 1) / NBBY || cpusetsize > CPU_MAXSIZE / NBBY)
 		return (ERANGE);
 	/* In Capability mode, you can only set your own CPU set. */
 	if (IN_CAPABILITY_MODE(td)) {
@@ -1221,7 +1221,7 @@ 
 	    if (id != -1)
 		return (ECAPMODE);
 	}
-	mask = malloc(cpusetsize, M_TEMP, M_WAITOK | M_ZERO);
+	mask = malloc(cpusetsize >= sizeof(cpuset_t) ? cpusetsize : sizeof(cpuset_t), M_TEMP, M_WAITOK | M_ZERO);
 	error = copyin(maskp, mask, cpusetsize);
 	if (error)
 		goto out;