scsi: sd: reject invalid pr_read_keys() num_keys values

The pr_read_keys() interface has a u32 num_keys parameter. The SCSI
PERSISTENT RESERVE IN command has a maximum READ KEYS service action
size of 65536 bytes. Reject num_keys values that are too large to fit
into the SCSI command.

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/scsi/sd.c

@@ -1974,9 +1974,19 @@ static int sd_pr_read_keys(struct block_device *bdev, struct pr_keys *keys_info)
 {
 	int result, i, data_offset, num_copy_keys;
 	u32 num_keys = keys_info->num_keys;
-	int data_len = num_keys * 8 + 8;
+	int data_len;
 	u8 *data;
 
+	/*
+	 * Each reservation key takes 8 bytes and there is an 8-byte header
+	 * before the reservation key list. The total size must fit into the
+	 * 16-bit ALLOCATION LENGTH field.
+	 */
+	if (check_mul_overflow(num_keys, 8, &data_len) ||
+	    check_add_overflow(data_len, 8, &data_len) ||
+	    data_len > USHRT_MAX)
+		return -EINVAL;
+
 	data = kzalloc(data_len, GFP_KERNEL);
 	if (!data)
 		return -ENOMEM;