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Subject[PATCH 1/6] ksm: limiting the num of mem regions user can register per fd.
Date
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");
--
1.5.6.5


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