linux-kernel - [PATCH v2 1/2] ipc sem: use kvmalloc for sem

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Message-ID: <a6354fd9-2d55-2e63-dd4d-fa7dc1d11134@virtuozzo.com>
Date:   Wed, 28 Apr 2021 10:35:15 +0300
From:   Vasily Averin <vvs@...tuozzo.com>
To:     Michal Hocko <mhocko@...e.com>, cgroups@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Alexey Dobriyan <adobriyan@...il.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Safonov <0x7f454c46@...il.com>
Subject: [PATCH v2 1/2] ipc sem: use kvmalloc for sem_undo allocation

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.

Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Reviewed-by: Shakeel Butt <shakeelb@...gle.com>
Acked-by: Roman Gushchin <guro@...com>
---
 ipc/sem.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index 52a6599..93088d6 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1152,7 +1152,7 @@ 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. */
@@ -1935,7 +1935,7 @@ 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,
+	new = kvzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems,
 		      GFP_KERNEL_ACCOUNT);
 	if (!new) {
 		ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
@@ -1948,7 +1948,7 @@ 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;
 	}
@@ -1959,7 +1959,7 @@ 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 +2420,7 @@ 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);
 }
-- 
1.8.3.1