nvme: reject invalid pr_read_keys() num_keys values

The pr_read_keys() interface has a u32 num_keys parameter. The NVMe
Reservation Report command has a u32 maximum length. Reject num_keys
values that are too large to fit.

This will become important when pr_read_keys() is exposed to untrusted
userspace via an <linux/pr.h> ioctl.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: stefanhaRH

drivers/nvme/host/pr.c

@@ -228,7 +228,8 @@ static int nvme_pr_resv_report(struct block_device *bdev, void *data,
 static int nvme_pr_read_keys(struct block_device *bdev,
 		struct pr_keys *keys_info)
 {
-	u32 rse_len, num_keys = keys_info->num_keys;
+	size_t rse_len;
+	u32 num_keys = keys_info->num_keys;
 	struct nvme_reservation_status_ext *rse;
 	int ret, i;
 	bool eds;
@@ -238,6 +239,9 @@ static int nvme_pr_read_keys(struct block_device *bdev,
 	 * enough to get enough keys to fill the return keys buffer.
 	 */
 	rse_len = struct_size(rse, regctl_eds, num_keys);
+	if (rse_len > U32_MAX)
+		return -EINVAL;
+
 	rse = kzalloc(rse_len, GFP_KERNEL);
 	if (!rse)
 		return -ENOMEM;