[PATCH v2 1/4] scsi: sd: reject invalid pr_read_keys() num_keys values

[Stefan Hajnoczi <stefanha@redhat.com>]

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>
---
 drivers/scsi/sd.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 0252d3f6bed17..e436ed977cdb4 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1974,9 +1974,18 @@ 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 (num_keys > (USHRT_MAX / 8) - 1)
+		return -EINVAL;
+
+	data_len = num_keys * 8 + 8;
 	data = kzalloc(data_len, GFP_KERNEL);
 	if (!data)
 		return -ENOMEM;
-- 
2.52.0