IPC: fix error case when idr-cache is empty in ipcget()

With the use of idr to store the ipc, the case where the idr cache is
empty, when idr_get_new is called (this may happen even if we call
idr_pre_get() before), is not well handled: it lets
semget()/shmget()/msgget() return ENOSPC when this cache is empty, what 1.
does not reflect the facts and 2.  does not conform to the man(s).

This patch fixes this by retrying the whole process of allocation in this case.

Signed-off-by: Pierre Peiffer <pierre.peiffer@bull.net>
Cc: Nadia Derbey <Nadia.Derbey@bull.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ipc/msg.c

@@ -203,10 +203,10 @@ static int newque(struct ipc_namespace *ns, struct ipc_params *params)
 	 * ipc_addid() locks msq
 	 */
 	id = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni);
-	if (id == -1) {
+	if (id < 0) {
 		security_msg_queue_free(msq);
 		ipc_rcu_putref(msq);
-		return -ENOSPC;
+		return id;
 	}
 
 	msq->q_perm.id = msg_buildid(id, msq->q_perm.seq);

ipc/sem.c

@@ -283,10 +283,10 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
 	}
 
 	id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
-	if(id == -1) {
+	if (id < 0) {
 		security_sem_free(sma);
 		ipc_rcu_putref(sma);
-		return -ENOSPC;
+		return id;
 	}
 	ns->used_sems += nsems;
 

ipc/shm.c

@@ -433,10 +433,11 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
 	if (IS_ERR(file))
 		goto no_file;
 
-	error = -ENOSPC;
 	id = shm_addid(ns, shp);
-	if(id == -1) 
+	if (id < 0) {
+		error = id;
 		goto no_id;
+	}
 
 	shp->shm_cprid = task_tgid_vnr(current);
 	shp->shm_lprid = 0;

ipc/util.c

@@ -262,7 +262,7 @@ int ipc_get_maxid(struct ipc_ids *ids)
  *	Add an entry 'new' to the IPC ids idr. The permissions object is
  *	initialised and the first free entry is set up and the id assigned
  *	is returned. The 'new' entry is returned in a locked state on success.
- *	On failure the entry is not locked and -1 is returned.
+ *	On failure the entry is not locked and a negative err-code is returned.
  *
  *	Called with ipc_ids.rw_mutex held as a writer.
  */
@@ -275,11 +275,11 @@ int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
 		size = IPCMNI;
 
 	if (ids->in_use >= size)
-		return -1;
+		return -ENOSPC;
 
 	err = idr_get_new(&ids->ipcs_idr, new, &id);
 	if (err)
-		return -1;
+		return err;
 
 	ids->in_use++;
 
@@ -311,7 +311,7 @@ int ipcget_new(struct ipc_namespace *ns, struct ipc_ids *ids,
 		struct ipc_ops *ops, struct ipc_params *params)
 {
 	int err;
-
+retry:
 	err = idr_pre_get(&ids->ipcs_idr, GFP_KERNEL);
 
 	if (!err)
@@ -321,6 +321,9 @@ int ipcget_new(struct ipc_namespace *ns, struct ipc_ids *ids,
 	err = ops->getnew(ns, params);
 	up_write(&ids->rw_mutex);
 
+	if (err == -EAGAIN)
+		goto retry;
+
 	return err;
 }
 
@@ -374,7 +377,7 @@ int ipcget_public(struct ipc_namespace *ns, struct ipc_ids *ids,
 	struct kern_ipc_perm *ipcp;
 	int flg = params->flg;
 	int err;
-
+retry:
 	err = idr_pre_get(&ids->ipcs_idr, GFP_KERNEL);
 
 	/*
@@ -411,6 +414,9 @@ int ipcget_public(struct ipc_namespace *ns, struct ipc_ids *ids,
 	}
 	up_write(&ids->rw_mutex);
 
+	if (err == -EAGAIN)
+		goto retry;
+
 	return err;
 }