xen/gntalloc: fix reference counts on multi-page mappings

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>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 43 insertions, 13 deletions

diff --git a/drivers/xen/gntalloc.c b/drivers/xen/gntalloc.c
index f330a4b8b685..e8ea56583b4c 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;