[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, 6 insertions, 4 deletions

diff --git a/drivers/media/v4l2-core/videobuf-dma-sg.c b/drivers/media/v4l2-core/videobuf-dma-sg.c
index 828e7c10bd70..9db674ccdc68 100644
--- a/drivers/media/v4l2-core/videobuf-dma-sg.c
+++ b/drivers/media/v4l2-core/videobuf-dma-sg.c
@@ -338,11 +338,14 @@ EXPORT_SYMBOL_GPL(videobuf_dma_free);
 static void videobuf_vm_open(struct vm_area_struct *vma)
 {
 	struct videobuf_mapping *map = vma->vm_private_data;
+	struct videobuf_queue *q = map->q;
 
 	dprintk(2, "vm_open %p [count=%d,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)
@@ -355,10 +358,9 @@ static void videobuf_vm_close(struct vm_area_struct *vma)
 	dprintk(2, "vm_close %p [count=%d,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) {
 		dprintk(1, "munmap %p q=%p\n", map, q);
-		videobuf_queue_lock(q);
 		for (i = 0; i < VIDEO_MAX_FRAME; i++) {
 			if (NULL == q->bufs[i])
 				continue;
@@ -374,9 +376,9 @@ static void videobuf_vm_close(struct vm_area_struct *vma)
 			q->bufs[i]->baddr = 0;
 			q->ops->buf_release(q, q->bufs[i]);
 		}
-		videobuf_queue_unlock(q);
 		kfree(map);
 	}
+	videobuf_queue_unlock(q);
 	return;
 }