ipc sem: use kvmalloc for sem_undo allocation

Patch series "ipc: allocations cleanup", v2.

Some ipc objects use the wrong allocation functions: small objects can use
kmalloc(), and vice versa, potentially large objects can use kmalloc().

This patch (of 2):

Size of sem_undo can exceed one page and with the maximum possible nsems =
32000 it can grow up to 64Kb.  Let's switch its allocation to kvmalloc to
avoid user-triggered disruptive actions like OOM killer in case of
high-order memory shortage.

User triggerable high order allocations are quite a problem on heavily
fragmented systems.  They can be a DoS vector.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Vasily Averin <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Reviewed-by: Shakeel Butt <[email protected]>
Acked-by: Roman Gushchin <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Dmitry Safonov <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Manfred Spraul <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

ipc/sem.c

@@ -1154,7 +1154,7 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
 		un->semid = -1;
 		list_del_rcu(&un->list_proc);
 		spin_unlock(&un->ulp->lock);
-		kfree_rcu(un, rcu);
+		kvfree_rcu(un, rcu);
 	}
 
 	/* Wake up all pending processes and let them fail with EIDRM. */
@@ -1937,7 +1937,8 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
 	rcu_read_unlock();
 
 	/* step 2: allocate new undo structure */
-	new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL);
+	new = kvzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems,
+		       GFP_KERNEL);
 	if (!new) {
 		ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
 		return ERR_PTR(-ENOMEM);
@@ -1949,7 +1950,7 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
 	if (!ipc_valid_object(&sma->sem_perm)) {
 		sem_unlock(sma, -1);
 		rcu_read_unlock();
-		kfree(new);
+		kvfree(new);
 		un = ERR_PTR(-EIDRM);
 		goto out;
 	}
@@ -1960,7 +1961,7 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
 	 */
 	un = lookup_undo(ulp, semid);
 	if (un) {
-		kfree(new);
+		kvfree(new);
 		goto success;
 	}
 	/* step 5: initialize & link new undo structure */
@@ -2420,7 +2421,7 @@ void exit_sem(struct task_struct *tsk)
 		rcu_read_unlock();
 		wake_up_q(&wake_q);
 
-		kfree_rcu(un, rcu);
+		kvfree_rcu(un, rcu);
 	}
 	kfree(ulp);
 }