[PATCH 09/13] ksm: limiting the num of mem regions user can register per fd.

[Izik Eidus]

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@xxxxxxxxxx>
---
 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