zoran: racy refcount handling in vm_ops ->open()/->close()

worse, we lock ->resource_lock too late when we are destroying the
final clonal VMA; the check for lack of other mappings of the same
opened file can race with mmap().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 9 insertions, 8 deletions

diff --git a/drivers/media/pci/zoran/zoran.h b/drivers/media/pci/zoran/zoran.h
index ca2754a3cd63..5e040085c2ff 100644
--- a/drivers/media/pci/zoran/zoran.h
+++ b/drivers/media/pci/zoran/zoran.h
@@ -176,7 +176,7 @@ struct zoran_fh;
 
 struct zoran_mapping {
         struct zoran_fh *fh;
-        int count;
+        atomic_t count;
 };
 
 struct zoran_buffer {
diff --git a/drivers/media/pci/zoran/zoran_driver.c b/drivers/media/pci/zoran/zoran_driver.c
index 1168a84a737d..d133c30c3fdc 100644
--- a/drivers/media/pci/zoran/zoran_driver.c
+++ b/drivers/media/pci/zoran/zoran_driver.c
@@ -2803,8 +2803,7 @@ static void
 zoran_vm_open (struct vm_area_struct *vma)
 {
         struct zoran_mapping *map = vma->vm_private_data;
-
-        map->count++;
+        atomic_inc(&map->count);
 }
 
 static void
@@ -2815,7 +2814,7 @@ zoran_vm_close (struct vm_area_struct *vma)
         struct zoran *zr = fh->zr;
         int i;
 
-        if (--map->count > 0)
+        if (!atomic_dec_and_mutex_lock(&map->count, &zr->resource_lock))
                 return;
 
         dprintk(3, KERN_INFO "%s: %s - munmap(%s)\n", ZR_DEVNAME(zr),
@@ -2828,14 +2827,16 @@ zoran_vm_close (struct vm_area_struct *vma)
         kfree(map);
 
         /* Any buffers still mapped? */
-        for (i = 0; i < fh->buffers.num_buffers; i++)
-                if (fh->buffers.buffer[i].map)
+        for (i = 0; i < fh->buffers.num_buffers; i++) {
+                if (fh->buffers.buffer[i].map) {
+                        mutex_unlock(&zr->resource_lock);
                         return;
+                }
+        }
 
         dprintk(3, KERN_INFO "%s: %s - free %s buffers\n", ZR_DEVNAME(zr),
                 __func__, mode_name(fh->map_mode));
 
-        mutex_lock(&zr->resource_lock);
 
         if (fh->map_mode == ZORAN_MAP_MODE_RAW) {
                 if (fh->buffers.active != ZORAN_FREE) {
@@ -2939,7 +2940,7 @@ zoran_mmap (struct file           *file,
                 goto mmap_unlock_and_return;
         }
         map->fh = fh;
-        map->count = 1;
+        atomic_set(&map->count, 1);
 
         vma->vm_ops = &zoran_vm_ops;
         vma->vm_flags |= VM_DONTEXPAND;