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
