diff --git a/conts/posix/mm0/mm/capability.c b/conts/posix/mm0/mm/capability.c
index 1e71661..2471408 100644
--- a/conts/posix/mm0/mm/capability.c
+++ b/conts/posix/mm0/mm/capability.c
@@ -347,73 +347,86 @@ int cap_find_replicate_reduce_grant(struct capability *cap)
 	struct capability new_cap;
 	int err;
 
-	/*
-	 * Check for type
-	 */
+	/* Merely match type, kernel does actual check on suitability */
 	list_foreach_struct(possessed, &capability_list.caps, list) {
-		if (cap_type(possessed) == cap_type(cap))
-			goto found;
+		/* Different type, pass */
+		if (cap_type(possessed) != cap_type(cap))
+			continue;
+
+		/* Copy possessed one to new one's buffer */
+		memcpy(&new_cap, possessed, sizeof(*possessed));
+
+		/* Replicate capability, giving original as reference */
+		if ((err = l4_capability_control(CAP_CONTROL_REPLICATE,
+						 0, 0, 0, &new_cap)) < 0) {
+			printf("l4_capability_control() replication of "
+			       "capability failed.\n Could not complete "
+			       "CAP_CONTROL_REPLICATE request on cap (%d), "
+			       "err = %d.\n", new_cap.capid, err);
+			return err;
+		}
+
+		/*
+		 * The returned capability is a replica.
+		 *
+		 * We don't add the newly created one to our own internal
+		 * list because we will grant it shortly and lose its
+		 * possession
+		 *
+		 * Now deduce it such that it looks like the one requested.
+		 * Note, we assume the request had been validated before.
+		 * Also note, the owner shall be still us.
+		 */
+		new_cap.resid = cap->resid;
+		new_cap.type = cap->type;
+		new_cap.access = cap->access;
+		new_cap.start = cap->start;
+		new_cap.end = cap->end;
+		new_cap.size = cap->size;
+		new_cap.used = cap->used;
+
+		/*
+		 * Make sure it is transferable,
+		 * since we will need to grant it soon
+		 */
+		new_cap.access |= CAP_TRANSFERABLE;
+
+
+		if ((err = l4_capability_control(CAP_CONTROL_DEDUCE,
+						 0, 0, 0, &new_cap)) < 0) {
+			/* Couldn't deduce this one, destroy the replica */
+			if ((err =
+			     l4_capability_control(CAP_CONTROL_DESTROY,
+						   0, 0, 0, &new_cap)) < 0) {
+				printf("l4_capability_control() replication of "
+				       "capability failed.\n Could not "
+				       "complete CAP_CONTROL_DESTROY request "
+				       " on cap (%d), err = %d.\n",
+				       new_cap.capid, err);
+				BUG();
+			}
+		} else /* Success */
+			goto success;
 	}
+
 	return -ENOCAP;
 
-found:
-	/* Copy possessed one to new one's buffer */
-	memcpy(&new_cap, possessed, sizeof(*possessed));
-
-	/* Replicate the possessed capability, giving original as reference */
-	if ((err = l4_capability_control(CAP_CONTROL_REPLICATE,
-					 0, 0, 0, &new_cap)) < 0) {
-		printf("l4_capability_control() replication of "
-		       "capability failed.\n Could not "
-		       "complete CAP_CONTROL_REPLICATE request on cap (%d), "
-		       "err = %d.\n", new_cap.capid, err);
-		return err;
-	}
-
+success:
 	/*
-	 * The returned capability is a replica.
+	 * Found suitable one to replicate/deduce.
+	 * Grant it to requested owner.
 	 *
-	 * We don't add the newly created one to our own internal
-	 * list because we will grant it shortly and lose its
-	 * possession
-	 *
-	 * Now deduce it such that it looks like the one requested.
-	 * Note, we assume the request had been validated before.
-	 */
-	new_cap.owner = cap->owner;
-	new_cap.resid = cap->resid;
-	new_cap.type = cap->type;
-	new_cap.access = cap->access;
-	new_cap.start = cap->start;
-	new_cap.end = cap->end;
-	new_cap.size = cap->size;
-	new_cap.used = cap->used;
-
-	/*
-	 * Make sure it is transferable,
-	 * since we will need to grant it soon
-	 */
-	new_cap.access |= CAP_TRANSFERABLE;
-
-	if ((err = l4_capability_control(CAP_CONTROL_DEDUCE,
-					 0, 0, 0, &new_cap)) < 0) {
-		printf("l4_capability_control() deduction of "
-		       "ipc capability failed.\n Could not "
-		       "complete CAP_CONTROL_DEDUCE request on cap (%d), "
-		       "err = %d.\n", new_cap.capid, err);
-		return err;
-	}
-
-	/*
-	 * Grant it to given owner.
-	 *
-	 * This effectively enables the owner to have all operations defined
-	 * in the capability. However, we use a flag to make the capability
-	 * immutable as we grant it. (We wouldn't be able to grant it if it
-	 * had no grant permission originally. We remove it as we grant it)
+	 * This effectively enables the owner to have all
+	 * operations defined in the capability. However,
+	 * we use a flag to make the capability immutable
+	 * as we grant it. (We wouldn't be able to grant
+	 * it if it had no grant permission originally. We
+	 * remove it _as_ we grant it)
 	 */
+	new_cap.owner = cap->owner; /* Indicate new owner */
 	if ((err = l4_capability_control(CAP_CONTROL_GRANT,
-					 CAP_GRANT_SINGLE | CAP_GRANT_IMMUTABLE,
+					 CAP_GRANT_SINGLE |
+					 CAP_GRANT_IMMUTABLE,
 					 0, 0, &new_cap)) < 0) {
 		printf("l4_capability_control() granting of "
 		       "capability (%d) failed.\n Could not "
@@ -493,8 +506,7 @@ int sys_request_cap(struct tcb *task, struct capability *__cap_userptr)
 	}
 
 out:
-	pager_unmap_user_range(__cap_userptr,
-			       sizeof(*__cap_userptr));
+	pager_unmap_user_range(cap, sizeof(*cap));
 	return ret;
 }
 
diff --git a/conts/posix/test0/src/ipctest.c b/conts/posix/test0/src/ipctest.c
index cb09614..bdd070a 100644
--- a/conts/posix/test0/src/ipctest.c
+++ b/conts/posix/test0/src/ipctest.c
@@ -105,11 +105,11 @@ void ipc_extended_test(void)
 		cap.owner = parent;
 		cap.resid = child;
 	} else {
-		cap.owner = child;
+		cap.owner = getpid();
 		cap.resid = parent;
 	}
 	cap.type = CAP_TYPE_IPC | CAP_RTYPE_THREAD;
-	cap.access = CAP_IPC_EXTENDED;
+	cap.access = CAP_IPC_EXTENDED | CAP_IPC_SEND | CAP_IPC_RECV;
 	if ((err = cap_request_pager(&cap)) < 0) {
 		printf("Ipc capability request failed. "
 		       "err = %d\n", err);
diff --git a/include/l4/api/capability.h b/include/l4/api/capability.h
index 82b1ddb..0e56e41 100644
--- a/include/l4/api/capability.h
+++ b/include/l4/api/capability.h
@@ -14,6 +14,7 @@
 #define CAP_CONTROL_REPLICATE		0x00000005
 #define CAP_CONTROL_SPLIT		0x00000006
 #define CAP_CONTROL_DEDUCE		0x00000007
+#define CAP_CONTROL_DESTROY		0x00000008
 
 #define CAP_SHARE_MASK			0x00000003
 #define CAP_SHARE_SINGLE		0x00000001
diff --git a/include/l4/generic/cap-types.h b/include/l4/generic/cap-types.h
index 3fe411e..0afad80 100644
--- a/include/l4/generic/cap-types.h
+++ b/include/l4/generic/cap-types.h
@@ -108,6 +108,7 @@
 #define CAP_CAP_REPLICATE	(1 << 3)
 #define CAP_CAP_SPLIT		(1 << 4)
 #define CAP_CAP_DEDUCE		(1 << 5)
-#define CAP_CAP_MODIFY		(CAP_CAP_SPLIT | CAP_CAP_DEDUCE)
-
+#define CAP_CAP_DESTROY		(1 << 6)
+#define CAP_CAP_MODIFY		(CAP_CAP_DEDUCE | CAP_CAP_SPLIT \
+				 | CAP_CAP_DESTROY)
 #endif /* __CAP_TYPES_H__ */
diff --git a/include/l4/generic/capability.h b/include/l4/generic/capability.h
index cee582e..9bc5623 100644
--- a/include/l4/generic/capability.h
+++ b/include/l4/generic/capability.h
@@ -99,6 +99,13 @@ static inline void cap_list_insert(struct capability *cap,
 	clist->ncaps++;
 }
 
+static inline void cap_list_remove(struct capability *cap,
+				   struct cap_list *clist)
+{
+	list_remove(&cap->list);
+	clist->ncaps--;
+}
+
 /* Detach a whole list of capabilities from list head */
 static inline struct capability *
 cap_list_detach(struct cap_list *clist)
@@ -141,6 +148,8 @@ struct capability *cap_list_find_by_rtype(struct cap_list *clist,
 					  unsigned int rtype);
 struct capability *cap_find_byid(l4id_t capid);
 
+int cap_find_destroy(l4id_t capid);
+
 /* Capability checking on system calls */
 int cap_map_check(struct ktcb *task, unsigned long phys, unsigned long virt,
 		  unsigned long npages, unsigned int flags);
diff --git a/src/api/cap.c b/src/api/cap.c
index dce2c3a..f2c5ff0 100644
--- a/src/api/cap.c
+++ b/src/api/cap.c
@@ -97,13 +97,14 @@ int cap_share(l4id_t capid, unsigned int flags)
 }
 
 /* Grants all caps */
-int cap_grant_all(l4id_t tid, unsigned int flags)
+int cap_grant_all(struct capability *req, unsigned int flags)
 {
 	struct ktcb *target;
 	struct capability *cap_head, *cap;
 	int err;
 
-	if (!(target = tcb_find(tid)))
+	/* Owners are always threads, for simplicity */
+	if (!(target = tcb_find(req->owner)))
 		return -ESRCH;
 
 	/* Detach all caps */
@@ -112,6 +113,7 @@ int cap_grant_all(l4id_t tid, unsigned int flags)
 	list_foreach_struct(cap, &cap_head->list, list) {
 		/* Change ownership */
 		cap->owner = target->tid;
+		BUG_ON(target->tid != req->owner);
 
 		/* Make immutable if GRANT_IMMUTABLE given */
 		if (flags & CAP_GRANT_IMMUTABLE) {
@@ -140,15 +142,15 @@ out_err:
 	return err;
 }
 
-int cap_grant_single(l4id_t capid, l4id_t tid, unsigned int flags)
+int cap_grant_single(struct capability *req, unsigned int flags)
 {
 	struct capability *cap;
 	struct ktcb *target;
 
-	if (!(cap = cap_find_byid(capid)))
+	if (!(cap = cap_find_byid(req->capid)))
 		return -EEXIST;
 
-	if (!(target = tcb_find(tid)))
+	if (!(target = tcb_find(req->owner)))
 		return -ESRCH;
 
 	if (cap->owner != current->tid)
@@ -163,6 +165,7 @@ int cap_grant_single(l4id_t capid, l4id_t tid, unsigned int flags)
 
 	/* Change ownership */
 	cap->owner = target->tid;
+	BUG_ON(cap->owner != req->owner);
 
 	/* Make immutable if GRANT_IMMUTABLE given */
 	if (flags & CAP_GRANT_IMMUTABLE) {
@@ -176,12 +179,12 @@ int cap_grant_single(l4id_t capid, l4id_t tid, unsigned int flags)
 	return 0;
 }
 
-int cap_grant(l4id_t capid, l4id_t tid, unsigned int flags)
+int cap_grant(struct capability *cap, unsigned int flags)
 {
 	if (flags & CAP_GRANT_SINGLE)
-		cap_grant_single(capid, tid, flags);
+		cap_grant_single(cap, flags);
 	else if (flags & CAP_GRANT_ALL)
-		cap_grant_all(tid, flags);
+		cap_grant_all(cap, flags);
 	else
 		return -EINVAL;
 	return 0;
@@ -288,6 +291,10 @@ int cap_deduce(struct capability *new)
 		if ((ret = cap_deduce_rtype(orig, new)) < 0)
 			return ret;
 
+	/* Check owners are same for request validity */
+	if (orig->owner != new->owner)
+		return -EINVAL;
+
 	/* Check permissions for deduction */
 	if (orig->access) {
 		/* New cannot have more bits than original */
@@ -340,6 +347,29 @@ int cap_deduce(struct capability *new)
 	return 0;
 }
 
+/*
+ * Destroys a capability
+ */
+int cap_destroy(struct capability *cap)
+{
+	struct capability *orig;
+
+	/* Find original capability */
+	if (!(orig = cap_find_byid(cap->capid)))
+		return -EEXIST;
+
+	/* Check that caller is owner */
+	if (orig->owner != current->tid)
+		return -ENOCAP;
+
+	/* Check that it is destroyable */
+	if (!(cap_generic_perms(orig) & CAP_CHANGEABLE))
+		return -ENOCAP;
+
+	cap_find_destroy(cap->capid);
+	return 0;
+}
+
 /*
  * Splits a capability
  *
@@ -374,6 +404,10 @@ int cap_split(struct capability *diff)
 	if (orig->owner != current->tid)
 		return -ENOCAP;
 
+	/* Check owners are same for request validity */
+	if (orig->owner != diff->owner)
+		return -EINVAL;
+
 	/* Check that it is splitable */
 	if (!(orig->access & CAP_CHANGEABLE))
 		return -ENOCAP;
@@ -427,6 +461,9 @@ int cap_split(struct capability *diff)
 	} else if (new->size)
 		return -EINVAL;
 
+	/* No used diff allowed for request validity */
+	if (diff->used)
+		return -EINVAL;
 
 	/* Check range usage but don't split if requested */
 	if (orig->start || orig->end) {
@@ -439,8 +476,6 @@ int cap_split(struct capability *diff)
 	} else if (new->start || new->end)
 		return -EINVAL;
 
-
-
 	/* Copy other fields */
 	new->type = orig->type;
 	new->resid = orig->resid;
@@ -557,14 +592,24 @@ int sys_capability_control(unsigned int req, unsigned int flags,
 		err = cap_share(capid, flags);
 		break;
 	case CAP_CONTROL_GRANT:
-		err = cap_grant(flags, capid, target);
+		if ((err = check_access((unsigned long)userbuf,
+					sizeof(struct capability),
+					MAP_USR_RW_FLAGS, 1)) < 0)
+			return err;
+
+		err = cap_grant((struct capability *)userbuf, flags);
 		break;
 	case CAP_CONTROL_SPLIT:
+		if ((err = check_access((unsigned long)userbuf,
+					sizeof(struct capability),
+					MAP_USR_RW_FLAGS, 1)) < 0)
+			return err;
+
 		err = cap_split((struct capability *)userbuf);
 		break;
 	case CAP_CONTROL_REPLICATE:
 		if ((err = check_access((unsigned long)userbuf,
-					sizeof(int),
+					sizeof(struct capability),
 					MAP_USR_RW_FLAGS, 1)) < 0)
 			return err;
 
@@ -572,12 +617,21 @@ int sys_capability_control(unsigned int req, unsigned int flags,
 		break;
 	case CAP_CONTROL_DEDUCE:
 		if ((err = check_access((unsigned long)userbuf,
-					sizeof(int),
+					sizeof(struct capability),
 					MAP_USR_RW_FLAGS, 1)) < 0)
 			return err;
 
 		err = cap_deduce((struct capability *)userbuf);
 		break;
+	case CAP_CONTROL_DESTROY:
+		if ((err = check_access((unsigned long)userbuf,
+					sizeof(struct capability),
+					MAP_USR_RW_FLAGS, 1)) < 0)
+			return err;
+
+		err = cap_destroy((struct capability *)userbuf);
+		break;
+
 	default:
 		/* Invalid request id */
 		return -EINVAL;
diff --git a/src/generic/capability.c b/src/generic/capability.c
index 194d2f9..9800340 100644
--- a/src/generic/capability.c
+++ b/src/generic/capability.c
@@ -154,6 +154,43 @@ struct capability *cap_find_byid(l4id_t capid)
 	return 0;
 }
 
+/*
+ * TODO: Instead of destroying, use cap_find_byid match function's
+ * match_args to pass a pointer to the capability list, so the
+ * caller may destroy it
+ */
+int cap_find_destroy(l4id_t capid)
+{
+	struct capability *cap;
+	struct ktcb *task = current;
+
+	/* Search task's own list */
+	list_foreach_struct(cap, &task->cap_list.caps, list)
+		if (cap->capid == capid) {
+			cap_list_remove(cap, &task->cap_list);
+			free_capability(cap);
+			return 0;
+		}
+
+	/* Search space list */
+	list_foreach_struct(cap, &task->space->cap_list.caps, list)
+		if (cap->capid == capid) {
+			cap_list_remove(cap, &task->space->cap_list);
+			free_capability(cap);
+			return 0;
+		}
+
+	/* Search container list */
+	list_foreach_struct(cap, &task->container->cap_list.caps, list)
+		if (cap->capid == capid) {
+			cap_list_remove(cap, &task->container->cap_list);
+			free_capability(cap);
+			return 0;
+		}
+
+	return -EEXIST;
+}
+
 typedef struct capability *(*cap_match_func_t) \
 		(struct capability *cap, void *match_args);
 
@@ -273,6 +310,9 @@ cap_match_capctrl(struct capability *cap, void *args_ptr)
 	if (req == CAP_CONTROL_DEDUCE)
 		if (!(cap->access & CAP_CAP_DEDUCE))
 			return 0;
+	if (req == CAP_CONTROL_DESTROY)
+		if (!(cap->access & CAP_CAP_DESTROY))
+			return 0;
 
 	/* Now check the usual restype/resid pair */
 	switch (cap_rtype(cap)) {