linux-kernel - [PATCH v3 1/4] scsi: sd: reject invalid pr_read_keys() num

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Message-ID: <20251201214329.933945-2-stefanha@redhat.com>
Date: Mon,  1 Dec 2025 16:43:26 -0500
From: Stefan Hajnoczi <stefanha@...hat.com>
To: linux-block@...r.kernel.org
Cc: Christoph Hellwig <hch@....de>,
	linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org,
	"James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Keith Busch <kbusch@...nel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Sagi Grimberg <sagi@...mberg.me>,
	Mike Christie <michael.christie@...cle.com>,
	Krzysztof Kozlowski <krzk@...nel.org>,
	linux-nvme@...ts.infradead.org,
	Stefan Hajnoczi <stefanha@...hat.com>
Subject: [PATCH v3 1/4] 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@...hat.com>
---
 drivers/scsi/sd.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 0252d3f6bed17..32ae4898cea7c 100644
--- a/drivers/scsi/sd.c
+++ b/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;
-- 
2.52.0