Re: [PATCH V2] Do not allow pagesize >= MAX_ORDER pool adjustment

[CAI Qian]

----- Original Message -----
> Huge pages with order >= MAX_ORDER must be allocated at boot via
> the kernel command line, they cannot be allocated or freed once
> the kernel is up and running. Currently we allow values to be
> written to the sysfs and sysctl files controling pool size for these
> huge page sizes. This patch makes the store functions for nr_hugepages
> and nr_overcommit_hugepages return -EINVAL when the pool for a
> page size >= MAX_ORDER is changed.
> 
> Reported-by: CAI Qian <caiqian@xxxxxxxxxx>
> 
> Signed-off-by: Eric B Munson <emunson@xxxxxxxxx>
> ---
> Changes from V1:
> Add check to sysctl handler
> 
> mm/hugetlb.c | 12 ++++++++++++
> 1 files changed, 12 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 5cb71a9..15bd633 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1443,6 +1443,12 @@ static ssize_t nr_hugepages_store_common(bool
> obey_mempolicy,
> return -EINVAL;
> 
> h = kobj_to_hstate(kobj, &nid);
> +
> + if (h->order >= MAX_ORDER) {
> + NODEMASK_FREE(nodes_allowed);
> + return -EINVAL;
> + }
> +
> if (nid == NUMA_NO_NODE) {
> /*
> * global hstate attribute
> @@ -1517,6 +1523,9 @@ static ssize_t
> nr_overcommit_hugepages_store(struct kobject *kobj,
> unsigned long input;
> struct hstate *h = kobj_to_hstate(kobj, NULL);
> 
> + if (h->order >= MAX_ORDER)
> + return -EINVAL;
> +
> err = strict_strtoul(buf, 10, &input);
> if (err)
> return -EINVAL;
> @@ -1926,6 +1935,9 @@ static int hugetlb_sysctl_handler_common(bool
> obey_mempolicy,
> if (!write)
> tmp = h->max_huge_pages;
> 
> + if (write && h->order >= MAX_ORDER)
> + return -EINVAL;
> +
> table->data = &tmp;
> table->maxlen = sizeof(unsigned long);
> proc_doulongvec_minmax(table, write, buffer, length, ppos);
> --
> 1.7.1
I believe this is still not enough. hugetlb_overcommit_handler() does not use
hugetlb_sysctl_handler_common() which also need this. Otherwise, people can
still abuse /proc/sys/vm/nr_overcommit_pages.

CAI Qian
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