Commit fc37a3b8 authored Jun 30, 2021 by Vasily Averin Committed by Linus Torvalds Jul 01, 2021

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/ebc3ac79-3190-520d-81ce-22ad194986ec@virtuozzo.com
Link: https://lkml.kernel.org/r/a6354fd9-2d55-2e63-dd4d-fa7dc1d11134@virtuozzo.com


Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Roman Gushchin <guro@fb.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 3b523483

ipc/sem.c

+6 −5

Original line number	Diff line number	Diff line
		@@ -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);
		}