X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=blobdiff_plain;f=ipc%2Futil.c;h=0af05752969f1bc4641a591d717edd1b46a18b5a;hb=eba2d6b34a32bdc3585c5810633ec38f9472380c;hp=fdffff41f65b546f66a5ee9b69297b39c445b8a0;hpb=5e26830990a9e8816b6854f77c550f1c847d89d8;p=linux.git

diff --git a/ipc/util.c b/ipc/util.c
index fdffff41f65b..0af05752969f 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -88,16 +88,12 @@ struct ipc_proc_iface {
  */
 static int __init ipc_init(void)
 {
-	int err_sem, err_msg;
-
 	proc_mkdir("sysvipc", NULL);
-	err_sem = sem_init();
-	WARN(err_sem, "ipc: sysv sem_init failed: %d\n", err_sem);
-	err_msg = msg_init();
-	WARN(err_msg, "ipc: sysv msg_init failed: %d\n", err_msg);
+	sem_init();
+	msg_init();
 	shm_init();
 
-	return err_msg ? err_msg : err_sem;
+	return 0;
 }
 device_initcall(ipc_init);
 
@@ -116,22 +112,17 @@ static const struct rhashtable_params ipc_kht_params = {
  * Set up the sequence range to use for the ipc identifier range (limited
  * below IPCMNI) then initialise the keys hashtable and ids idr.
  */
-int ipc_init_ids(struct ipc_ids *ids)
+void ipc_init_ids(struct ipc_ids *ids)
 {
-	int err;
 	ids->in_use = 0;
 	ids->seq = 0;
 	init_rwsem(&ids->rwsem);
-	err = rhashtable_init(&ids->key_ht, &ipc_kht_params);
-	if (err)
-		return err;
+	rhashtable_init(&ids->key_ht, &ipc_kht_params);
 	idr_init(&ids->ipcs_idr);
-	ids->tables_initialized = true;
-	ids->max_id = -1;
+	ids->max_idx = -1;
 #ifdef CONFIG_CHECKPOINT_RESTORE
 	ids->next_id = -1;
 #endif
-	return 0;
 }
 
 #ifdef CONFIG_PROC_FS
@@ -179,61 +170,66 @@ void __init ipc_init_proc_interface(const char *path, const char *header,
  */
 static struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key)
 {
-	struct kern_ipc_perm *ipcp = NULL;
+	struct kern_ipc_perm *ipcp;
 
-	if (likely(ids->tables_initialized))
-		ipcp = rhashtable_lookup_fast(&ids->key_ht, &key,
+	ipcp = rhashtable_lookup_fast(&ids->key_ht, &key,
 					      ipc_kht_params);
+	if (!ipcp)
+		return NULL;
 
-	if (ipcp) {
-		rcu_read_lock();
-		ipc_lock_object(ipcp);
-		return ipcp;
-	}
-
-	return NULL;
+	rcu_read_lock();
+	ipc_lock_object(ipcp);
+	return ipcp;
 }
 
-#ifdef CONFIG_CHECKPOINT_RESTORE
 /*
- * Specify desired id for next allocated IPC object.
+ * Insert new IPC object into idr tree, and set sequence number and id
+ * in the correct order.
+ * Especially:
+ * - the sequence number must be set before inserting the object into the idr,
+ *   because the sequence number is accessed without a lock.
+ * - the id can/must be set after inserting the object into the idr.
+ *   All accesses must be done after getting kern_ipc_perm.lock.
+ *
+ * The caller must own kern_ipc_perm.lock.of the new object.
+ * On error, the function returns a (negative) error code.
  */
-#define ipc_idr_alloc(ids, new)						\
-	idr_alloc(&(ids)->ipcs_idr, (new),				\
-		  (ids)->next_id < 0 ? 0 : ipcid_to_idx((ids)->next_id),\
-		  0, GFP_NOWAIT)
-
-static inline int ipc_buildid(int id, struct ipc_ids *ids,
-			      struct kern_ipc_perm *new)
+static inline int ipc_idr_alloc(struct ipc_ids *ids, struct kern_ipc_perm *new)
 {
-	if (ids->next_id < 0) { /* default, behave as !CHECKPOINT_RESTORE */
+	int idx, next_id = -1;
+
+#ifdef CONFIG_CHECKPOINT_RESTORE
+	next_id = ids->next_id;
+	ids->next_id = -1;
+#endif
+
+	/*
+	 * As soon as a new object is inserted into the idr,
+	 * ipc_obtain_object_idr() or ipc_obtain_object_check() can find it,
+	 * and the lockless preparations for ipc operations can start.
+	 * This means especially: permission checks, audit calls, allocation
+	 * of undo structures, ...
+	 *
+	 * Thus the object must be fully initialized, and if something fails,
+	 * then the full tear-down sequence must be followed.
+	 * (i.e.: set new->deleted, reduce refcount, call_rcu())
+	 */
+
+	if (next_id < 0) { /* !CHECKPOINT_RESTORE or next_id is unset */
 		new->seq = ids->seq++;
 		if (ids->seq > IPCID_SEQ_MAX)
 			ids->seq = 0;
+		idx = idr_alloc(&ids->ipcs_idr, new, 0, 0, GFP_NOWAIT);
 	} else {
-		new->seq = ipcid_to_seqx(ids->next_id);
-		ids->next_id = -1;
+		new->seq = ipcid_to_seqx(next_id);
+		idx = idr_alloc(&ids->ipcs_idr, new, ipcid_to_idx(next_id),
+				0, GFP_NOWAIT);
 	}
-
-	return SEQ_MULTIPLIER * new->seq + id;
+	if (idx >= 0)
+		new->id = SEQ_MULTIPLIER * new->seq + idx;
+	return idx;
 }
 
-#else
-#define ipc_idr_alloc(ids, new)					\
-	idr_alloc(&(ids)->ipcs_idr, (new), 0, 0, GFP_NOWAIT)
-
-static inline int ipc_buildid(int id, struct ipc_ids *ids,
-			      struct kern_ipc_perm *new)
-{
-	new->seq = ids->seq++;
-	if (ids->seq > IPCID_SEQ_MAX)
-		ids->seq = 0;
-
-	return SEQ_MULTIPLIER * new->seq + id;
-}
-
-#endif /* CONFIG_CHECKPOINT_RESTORE */
-
 /**
  * ipc_addid - add an ipc identifier
  * @ids: ipc identifier set
@@ -241,9 +237,11 @@ static inline int ipc_buildid(int id, struct ipc_ids *ids,
  * @limit: limit for the number of used 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
+ * initialised and the first free entry is set up and the index assigned
  * is returned. The 'new' entry is returned in a locked state on success.
+ *
  * On failure the entry is not locked and a negative err-code is returned.
+ * The caller must use ipc_rcu_putref() to free the identifier.
  *
  * Called with writer ipc_ids.rwsem held.
  */
@@ -251,19 +249,20 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit)
 {
 	kuid_t euid;
 	kgid_t egid;
-	int id, err;
+	int idx, err;
+
+	/* 1) Initialize the refcount so that ipc_rcu_putref works */
+	refcount_set(&new->refcount, 1);
 
 	if (limit > IPCMNI)
 		limit = IPCMNI;
 
-	if (!ids->tables_initialized || ids->in_use >= limit)
+	if (ids->in_use >= limit)
 		return -ENOSPC;
 
 	idr_preload(GFP_KERNEL);
 
-	refcount_set(&new->refcount, 1);
 	spin_lock_init(&new->lock);
-	new->deleted = false;
 	rcu_read_lock();
 	spin_lock(&new->lock);
 
@@ -271,30 +270,30 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit)
 	new->cuid = new->uid = euid;
 	new->gid = new->cgid = egid;
 
-	id = ipc_idr_alloc(ids, new);
+	new->deleted = false;
+
+	idx = ipc_idr_alloc(ids, new);
 	idr_preload_end();
 
-	if (id >= 0 && new->key != IPC_PRIVATE) {
+	if (idx >= 0 && new->key != IPC_PRIVATE) {
 		err = rhashtable_insert_fast(&ids->key_ht, &new->khtnode,
 					     ipc_kht_params);
 		if (err < 0) {
-			idr_remove(&ids->ipcs_idr, id);
-			id = err;
+			idr_remove(&ids->ipcs_idr, idx);
+			idx = err;
 		}
 	}
-	if (id < 0) {
+	if (idx < 0) {
+		new->deleted = true;
 		spin_unlock(&new->lock);
 		rcu_read_unlock();
-		return id;
+		return idx;
 	}
 
 	ids->in_use++;
-	if (id > ids->max_id)
-		ids->max_id = id;
-
-	new->id = ipc_buildid(id, ids, new);
-
-	return id;
+	if (idx > ids->max_idx)
+		ids->max_idx = idx;
+	return idx;
 }
 
 /**
@@ -432,20 +431,20 @@ static void ipc_kht_remove(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)
  */
 void ipc_rmid(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)
 {
-	int lid = ipcid_to_idx(ipcp->id);
+	int idx = ipcid_to_idx(ipcp->id);
 
-	idr_remove(&ids->ipcs_idr, lid);
+	idr_remove(&ids->ipcs_idr, idx);
 	ipc_kht_remove(ids, ipcp);
 	ids->in_use--;
 	ipcp->deleted = true;
 
-	if (unlikely(lid == ids->max_id)) {
+	if (unlikely(idx == ids->max_idx)) {
 		do {
-			lid--;
-			if (lid == -1)
+			idx--;
+			if (idx == -1)
 				break;
-		} while (!idr_find(&ids->ipcs_idr, lid));
-		ids->max_id = lid;
+		} while (!idr_find(&ids->ipcs_idr, idx));
+		ids->max_idx = idx;
 	}
 }
 
@@ -463,7 +462,7 @@ void ipc_set_key_private(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)
 	ipcp->key = IPC_PRIVATE;
 }
 
-int ipc_rcu_getref(struct kern_ipc_perm *ptr)
+bool ipc_rcu_getref(struct kern_ipc_perm *ptr)
 {
 	return refcount_inc_not_zero(&ptr->refcount);
 }
@@ -565,61 +564,22 @@ void ipc64_perm_to_ipc_perm(struct ipc64_perm *in, struct ipc_perm *out)
 struct kern_ipc_perm *ipc_obtain_object_idr(struct ipc_ids *ids, int id)
 {
 	struct kern_ipc_perm *out;
-	int lid = ipcid_to_idx(id);
-
-	if (unlikely(!ids->tables_initialized))
-		return ERR_PTR(-EINVAL);
+	int idx = ipcid_to_idx(id);
 
-	out = idr_find(&ids->ipcs_idr, lid);
+	out = idr_find(&ids->ipcs_idr, idx);
 	if (!out)
 		return ERR_PTR(-EINVAL);
 
 	return out;
 }
 
-/**
- * ipc_lock - lock an ipc structure without rwsem held
- * @ids: ipc identifier set
- * @id: ipc id to look for
- *
- * Look for an id in the ipc ids idr and lock the associated ipc object.
- *
- * The ipc object is locked on successful exit.
- */
-struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
-{
-	struct kern_ipc_perm *out;
-
-	rcu_read_lock();
-	out = ipc_obtain_object_idr(ids, id);
-	if (IS_ERR(out))
-		goto err;
-
-	spin_lock(&out->lock);
-
-	/*
-	 * ipc_rmid() may have already freed the ID while ipc_lock()
-	 * was spinning: here verify that the structure is still valid.
-	 * Upon races with RMID, return -EIDRM, thus indicating that
-	 * the ID points to a removed identifier.
-	 */
-	if (ipc_valid_object(out))
-		return out;
-
-	spin_unlock(&out->lock);
-	out = ERR_PTR(-EIDRM);
-err:
-	rcu_read_unlock();
-	return out;
-}
-
 /**
  * ipc_obtain_object_check
  * @ids: ipc identifier set
  * @id: ipc id to look for
  *
- * Similar to ipc_obtain_object_idr() but also checks
- * the ipc object reference counter.
+ * Similar to ipc_obtain_object_idr() but also checks the ipc object
+ * sequence number.
  *
  * Call inside the RCU critical section.
  * The ipc object is *not* locked on exit.
@@ -677,7 +637,7 @@ int ipc_update_perm(struct ipc64_perm *in, struct kern_ipc_perm *out)
 }
 
 /**
- * ipcctl_pre_down_nolock - retrieve an ipc and check permissions for some IPC_XXX cmd
+ * ipcctl_obtain_check - retrieve an ipc object and check permissions
  * @ns:  ipc namespace
  * @ids:  the table of ids where to look for the ipc
  * @id:   the id of the ipc to retrieve
@@ -687,16 +647,16 @@ int ipc_update_perm(struct ipc64_perm *in, struct kern_ipc_perm *out)
  *
  * This function does some common audit and permissions check for some IPC_XXX
  * cmd and is called from semctl_down, shmctl_down and msgctl_down.
- * It must be called without any lock held and:
  *
- *   - retrieves the ipc with the given id in the given table.
+ * It:
+ *   - retrieves the ipc object with the given id in the given table.
  *   - performs some audit and permission check, depending on the given cmd
  *   - returns a pointer to the ipc object or otherwise, the corresponding
  *     error.
  *
  * Call holding the both the rwsem and the rcu read lock.
  */
-struct kern_ipc_perm *ipcctl_pre_down_nolock(struct ipc_namespace *ns,
+struct kern_ipc_perm *ipcctl_obtain_check(struct ipc_namespace *ns,
 					struct ipc_ids *ids, int id, int cmd,
 					struct ipc64_perm *perm, int extra_perm)
 {