Re: [PATCH 1/6] ksm: limiting the num of mem regions user can register per fd.

Rik van Riel
2009-05-03T02:14:38Z

On Sun, 3 May 2009 01:16:07 +0300
Izik Eidus <ieidus@redhat.com> wrote:

> Right now user can open /dev/ksm fd and register unlimited number of
> regions, such behavior may allocate unlimited amount of kernel memory
> and get the whole host into out of memory situation.
>
> Signed-off-by: Izik Eidus <ieidus@redhat.com>
> ---
> mm/ksm.c | 15 +++++++++++++++
> 1 files changed, 15 insertions(+), 0 deletions(-)
>
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 6165276..d58db6b 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -48,6 +48,9 @@ static int rmap_hash_size;
> module_param(rmap_hash_size, int, 0);
> MODULE_PARM_DESC(rmap_hash_size, "Hash table size for the reverse
> mapping");
> +static int regions_per_fd;
> +module_param(regions_per_fd, int, 0);
> +
> /*
> * ksm_mem_slot - hold information for an userspace scanning range
> * (the scanning for this region will be from addr untill addr +
> @@ -67,6 +70,7 @@ struct ksm_mem_slot {
> */
> struct ksm_sma {
> struct list_head sma_slots;
> + int nregions;
> };
>
> /**
> @@ -453,6 +457,11 @@ static int
> ksm_sma_ioctl_register_memory_region(struct ksm_sma *ksm_sma, struct
> ksm_mem_slot *slot; int ret = -EPERM;
>
> + if ((ksm_sma->nregions + 1) > regions_per_fd) {
> + ret = -EBUSY;
> + goto out;
> + }
> +
> slot = kzalloc(sizeof(struct ksm_mem_slot), GFP_KERNEL);
> if (!slot) {
> ret = -ENOMEM;
> @@ -473,6 +482,7 @@ static int
> ksm_sma_ioctl_register_memory_region(struct ksm_sma *ksm_sma,
> list_add_tail(&slot->link, &slots);
> list_add_tail(&slot->sma_link, &ksm_sma->sma_slots);
> + ksm_sma->nregions++;
>
> up_write(&slots_lock);
> return 0;
> @@ -511,6 +521,7 @@ static int
> ksm_sma_ioctl_remove_memory_region(struct ksm_sma *ksm_sma)
> mmput(slot->mm); list_del(&slot->sma_link);
> kfree(slot);
> + ksm_sma->nregions--;
> }
> up_write(&slots_lock);
> return 0;
> @@ -1389,6 +1400,7 @@ static int
> ksm_dev_ioctl_create_shared_memory_area(void) }
>
> INIT_LIST_HEAD(&ksm_sma->sma_slots);
> + ksm_sma->nregions = 0;
>
> fd = anon_inode_getfd("ksm-sma", &ksm_sma_fops, ksm_sma, 0);
> if (fd < 0)
> @@ -1631,6 +1643,9 @@ static int __init ksm_init(void)
> if (r)
> goto out_free1;
>
> + if (!regions_per_fd)
> + regions_per_fd = 1024;
> +
> ksm_thread = kthread_run(ksm_scan_thread, NULL, "kksmd");
> if (IS_ERR(ksm_thread)) {
> printk(KERN_ERR "ksm: creating kthread failed\n");

--
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