[PATCH] scsi: core: bound the VPD page 0x83 designator walk

[Michael Bommarito <michael.bommarito@gmail.com>]

scsi_vpd_lun_id(), scsi_vpd_tpg_id() and sd_get_unique_id() walk the VPD
page 0x83 designator list with a stride of d[3] + 4 taken from the
device-supplied designator length d[3], without checking it against the
bytes remaining in the page. A device, or a compromised virtio/hypervisor
block backend, that returns a page 0x83 whose final designator length runs
past vpd_pg83->len makes the walk read out of bounds of the cached VPD
buffer.

Impact: a malicious or malfunctioning SCSI device, or a compromised
hypervisor block backend, drives an out-of-bounds read of the cached VPD
page 0x83 buffer (KASAN) during LUN-id, target-port-group, or unique-id
computation.

Bound each iteration: stop the walk when fewer than four header bytes
remain and when the designator length exceeds the bytes left in the page,
in all three walkers.

Fixes: 9983bed3907c ("scsi: Add scsi_vpd_lun_id()")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
---
 drivers/scsi/scsi_lib.c | 27 ++++++++++++++++++++-------
 drivers/scsi/sd.c       | 10 +++++++++-
 2 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 22e2e3223440d..407440bbf46c1 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -3375,6 +3375,7 @@ int scsi_vpd_lun_id(struct scsi_device *sdev, char *id, size_t id_len)
 	u8 cur_id_size = 0;
 	const unsigned char *d, *cur_id_str;
 	const struct scsi_vpd *vpd_pg83;
+	size_t off;
 	int id_size = -EINVAL;
 
 	rcu_read_lock();
@@ -3391,11 +3392,17 @@ int scsi_vpd_lun_id(struct scsi_device *sdev, char *id, size_t id_len)
 	}
 
 	memset(id, 0, id_len);
-	for (d = vpd_pg83->data + 4;
-	     d < vpd_pg83->data + vpd_pg83->len;
-	     d += d[3] + 4) {
-		u8 prio = designator_prio(d);
+	for (off = 4; off < vpd_pg83->len; off += d[3] + 4) {
+		u8 prio;
 
+		if (vpd_pg83->len - off < 4)
+			break;
+
+		d = vpd_pg83->data + off;
+		if (d[3] > vpd_pg83->len - off - 4)
+			break;
+
+		prio = designator_prio(d);
 		if (prio == 0 || cur_id_prio > prio)
 			continue;
 
@@ -3545,6 +3552,7 @@ int scsi_vpd_tpg_id(struct scsi_device *sdev, int *rel_id)
 {
 	const unsigned char *d;
 	const struct scsi_vpd *vpd_pg83;
+	size_t off;
 	int group_id = -EAGAIN, rel_port = -1;
 
 	rcu_read_lock();
@@ -3554,8 +3562,14 @@ int scsi_vpd_tpg_id(struct scsi_device *sdev, int *rel_id)
 		return -ENXIO;
 	}
 
-	d = vpd_pg83->data + 4;
-	while (d < vpd_pg83->data + vpd_pg83->len) {
+	for (off = 4; off < vpd_pg83->len; off += d[3] + 4) {
+		if (vpd_pg83->len - off < 4)
+			break;
+
+		d = vpd_pg83->data + off;
+		if (d[3] > vpd_pg83->len - off - 4)
+			break;
+
 		switch (d[1] & 0xf) {
 		case 0x4:
 			/* Relative target port */
@@ -3568,7 +3582,6 @@ int scsi_vpd_tpg_id(struct scsi_device *sdev, int *rel_id)
 		default:
 			break;
 		}
-		d += d[3] + 4;
 	}
 	rcu_read_unlock();
 
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 599e75f333343..5b8fa74052f2e 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1949,6 +1949,7 @@ static int sd_get_unique_id(struct gendisk *disk, u8 id[16],
 	struct scsi_device *sdev = scsi_disk(disk)->device;
 	const struct scsi_vpd *vpd;
 	const unsigned char *d;
+	size_t off;
 	int ret = -ENXIO, len;
 
 	rcu_read_lock();
@@ -1957,7 +1958,14 @@ static int sd_get_unique_id(struct gendisk *disk, u8 id[16],
 		goto out_unlock;
 
 	ret = -EINVAL;
-	for (d = vpd->data + 4; d < vpd->data + vpd->len; d += d[3] + 4) {
+	for (off = 4; off < vpd->len; off += d[3] + 4) {
+		if (vpd->len - off < 4)
+			break;
+
+		d = vpd->data + off;
+		if (d[3] > vpd->len - off - 4)
+			break;
+
 		/* we only care about designators with LU association */
 		if (((d[1] >> 4) & 0x3) != 0x00)
 			continue;
-- 
2.53.0