[media] videobuf_vm_{open,close} race fixes

just use videobuf_queue_lock(map->q) to protect map->count; vm_area_operations
->open() and ->close() are called just under vma->vm_mm->mmap_sem, which
doesn't help the drivers at all, since clonal VMAs are normally in different
address spaces...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/drivers/media/v4l2-core/videobuf-dma-contig.c b/drivers/media/v4l2-core/videobuf-dma-contig.c
index 67f572c3fba2..8204c8810372 100644
--- a/drivers/media/v4l2-core/videobuf-dma-contig.c
+++ b/drivers/media/v4l2-core/videobuf-dma-contig.c
@@ -66,11 +66,14 @@ static void __videobuf_dc_free(struct device *dev,
 static void videobuf_vm_open(struct vm_area_struct *vma)
 {
 	struct videobuf_mapping *map = vma->vm_private_data;
+	struct videobuf_queue *q = map->q;
 
-	dev_dbg(map->q->dev, "vm_open %p [count=%u,vma=%08lx-%08lx]\n",
+	dev_dbg(q->dev, "vm_open %p [count=%u,vma=%08lx-%08lx]\n",
 		map, map->count, vma->vm_start, vma->vm_end);
 
+	videobuf_queue_lock(q);
 	map->count++;
+	videobuf_queue_unlock(q);
 }
 
 static void videobuf_vm_close(struct vm_area_struct *vma)
@@ -82,12 +85,11 @@ static void videobuf_vm_close(struct vm_area_struct *vma)
 	dev_dbg(q->dev, "vm_close %p [count=%u,vma=%08lx-%08lx]\n",
 		map, map->count, vma->vm_start, vma->vm_end);
 
-	map->count--;
-	if (0 == map->count) {
+	videobuf_queue_lock(q);
+	if (!--map->count) {
 		struct videobuf_dma_contig_memory *mem;
 
 		dev_dbg(q->dev, "munmap %p q=%p\n", map, q);
-		videobuf_queue_lock(q);
 
 		/* We need first to cancel streams, before unmapping */
 		if (q->streaming)
@@ -126,8 +128,8 @@ static void videobuf_vm_close(struct vm_area_struct *vma)
 
 		kfree(map);
 
-		videobuf_queue_unlock(q);
 	}
+	videobuf_queue_unlock(q);
 }
 
 static const struct vm_operations_struct videobuf_vm_ops = {