Re: [PATCH 1/2] ipc sem: use kvmalloc for sem_undo allocation

[Michal Hocko]

On Mon 26-04-21 13:18:09, Vasily Averin wrote:
> 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@xxxxxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  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

-- 
Michal Hocko
SUSE Labs