Mailing List Archive

When a multi-page mapping of gntalloc is created, the reference counts
of all pages in the vma are incremented. However, the vma open/close
operations only adjusted the reference count of the first page in the
mapping, leaking the other pages. Store a struct in the vm_private_data
to track the original page count to properly free the pages when the
last reference to the vma is closed.

Reported-by: Anil Madhavapeddy <anil@recoil.org>
Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
---
drivers/xen/gntalloc.c | 56 ++++++++++++++++++++++++++++++++++++-----------
1 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/drivers/xen/gntalloc.c b/drivers/xen/gntalloc.c
index 7b936cc..e2400c8 100644
--- a/drivers/xen/gntalloc.c
+++ b/drivers/xen/gntalloc.c
@@ -99,6 +99,12 @@ struct gntalloc_file_private_data {
uint64_t index;
};

+struct gntalloc_vma_private_data {
+ struct gntalloc_gref *gref;
+ int users;
+ int count;
+};
+
static void __del_gref(struct gntalloc_gref *gref);

static void do_cleanup(void)
@@ -451,25 +457,39 @@ static long gntalloc_ioctl(struct file *filp, unsigned int cmd,

static void gntalloc_vma_open(struct vm_area_struct *vma)
{
- struct gntalloc_gref *gref = vma->vm_private_data;
- if (!gref)
+ struct gntalloc_vma_private_data *priv = vma->vm_private_data;
+
+ if (!priv)
return;

mutex_lock(&gref_mutex);
- gref->users++;
+ priv->users++;
mutex_unlock(&gref_mutex);
}

static void gntalloc_vma_close(struct vm_area_struct *vma)
{
- struct gntalloc_gref *gref = vma->vm_private_data;
- if (!gref)
+ struct gntalloc_vma_private_data *priv = vma->vm_private_data;
+ struct gntalloc_gref *gref, *next;
+ int i;
+
+ if (!priv)
return;

mutex_lock(&gref_mutex);
- gref->users--;
- if (gref->users == 0)
- __del_gref(gref);
+ priv->users--;
+ if (priv->users == 0) {
+ gref = priv->gref;
+ for (i = 0; i < priv->count; i++) {
+ gref->users--;
+ next = list_entry(gref->next_gref.next,
+ struct gntalloc_gref, next_gref);
+ if (gref->users == 0)
+ __del_gref(gref);
+ gref = next;
+ }
+ kfree(priv);
+ }
mutex_unlock(&gref_mutex);
}

@@ -481,19 +501,25 @@ static struct vm_operations_struct gntalloc_vmops = {
static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma)
{
struct gntalloc_file_private_data *priv = filp->private_data;
+ struct gntalloc_vma_private_data *vm_priv;
struct gntalloc_gref *gref;
int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
int rv, i;

- pr_debug("%s: priv %p, page %lu+%d\n", __func__,
- priv, vma->vm_pgoff, count);
-
if (!(vma->vm_flags & VM_SHARED)) {
printk(KERN_ERR "%s: Mapping must be shared.\n", __func__);
return -EINVAL;
}

+ vm_priv = kmalloc(sizeof(*vm_priv), GFP_KERNEL);
+ if (!vm_priv)
+ return -ENOMEM;
+
mutex_lock(&gref_mutex);
+
+ pr_debug("%s: priv %p,%p, page %lu+%d\n", __func__,
+ priv, vm_priv, vma->vm_pgoff, count);
+
gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count);
if (gref == NULL) {
rv = -ENOENT;
@@ -502,9 +528,13 @@ static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma)
goto out_unlock;
}

- vma->vm_private_data = gref;
+ vm_priv->gref = gref;
+ vm_priv->users = 1;
+ vm_priv->count = count;
+
+ vma->vm_private_data = vm_priv;

- vma->vm_flags |= VM_RESERVED;
+ vma->vm_flags |= VM_RESERVED | VM_DONTEXPAND;

vma->vm_ops = &gntalloc_vmops;

--
1.7.7.3


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