media: videobuf2: improve max_num_buffers sanity checks

Ensure that drivers set max_num_buffers to a value >= 32.
For now there is no reason for drivers to request a lower
limit and doing so might potentially cause userspace issues.
Note that the old check of > MAX_BUFFER_INDEX was pointless
since q->max_num_buffers was already limited to MAX_BUFFER_INDEX
or less.

Also add a sanity check in __vb2_init_fileio(), returning
-ENOSPC if a driver returns more than 32 buffers from
VIDIOC_REQBUFS with count = q->min_reqbufs_allocation.

The vb2_fileio_data struct only supports up to 32 buffers,
so we need a check there.

Signed-off-by: Hans Verkuil <[e-mail]>

drivers/media/common/videobuf2/videobuf2-core.c

···
 	    WARN_ON(!q->ops->buf_queue))
 		return -EINVAL;
 
-	if (WARN_ON(q->max_num_buffers > MAX_BUFFER_INDEX) ||
+	if (WARN_ON(q->max_num_buffers < VB2_MAX_FRAME) ||
 	    WARN_ON(q->min_queued_buffers > q->max_num_buffers))
 		return -EINVAL;
 
···
 	ret = vb2_core_reqbufs(q, fileio->memory, 0, &fileio->count);
 	if (ret)
 		goto err_kfree;
+	/* vb2_fileio_data supports max VB2_MAX_FRAME buffers */
+	if (fileio->count > VB2_MAX_FRAME) {
+		dprintk(q, 1, "fileio: more than VB2_MAX_FRAME buffers requested\n");
+		ret = -ENOSPC;
+		goto err_reqbufs;
+	}
 
 	/*
 	 * Userspace can never add or delete buffers later, so there