[PATCH] scsi: sd: bound the IO hints descriptor walk to the buffer

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

sd_read_io_hints() computes the end of the IO group descriptor list from
the mode-sense reply as buffer + (data.header_length + data.length),
where data.length is the device-reported mode data length. A device (or a
compromised virtio/hypervisor block backend) that reports a length larger
than the SD_BUF_SIZE buffer scsi_mode_sense() actually filled makes the
subsequent "for (desc = start; desc < end; desc++)" loop read past the
buffer.

Impact: a malicious or malfunctioning SCSI/SATA device, or a compromised
hypervisor block backend, drives an out-of-bounds read of the mode-sense
buffer (KASAN) while parsing permanent-stream IO hints at attach time.

Clamp the descriptor region to SD_BUF_SIZE before deriving the end
pointer.

Fixes: 4f53138fffc2 ("scsi: sd: Translate data lifetime information")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
---
 drivers/scsi/sd.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 599e75f333343..eec383cbc39f1 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -3304,6 +3304,7 @@ static void sd_read_io_hints(struct scsi_disk *sdkp, unsigned char *buffer)
 	struct scsi_sense_hdr sshdr;
 	struct scsi_mode_data data;
 	int res;
+	u32 len;
 
 	if (sdp->sdev_bflags & BLIST_SKIP_IO_HINTS)
 		return;
@@ -3313,9 +3314,17 @@ static void sd_read_io_hints(struct scsi_disk *sdkp, unsigned char *buffer)
 			      sdkp->max_retries, &data, &sshdr);
 	if (res < 0)
 		return;
+	/*
+	 * The device-reported mode data length can exceed the buffer that
+	 * was actually transferred; clamp it so the descriptor walk stays
+	 * within buffer[SD_BUF_SIZE].
+	 */
+	if (data.length > SD_BUF_SIZE - data.header_length)
+		len = SD_BUF_SIZE;
+	else
+		len = data.header_length + data.length;
 	start = (void *)buffer + data.header_length + 16;
-	end = (void *)buffer + ALIGN_DOWN(data.header_length + data.length,
-					  sizeof(*end));
+	end = (void *)buffer + ALIGN_DOWN(len, sizeof(*end));
 	/*
 	 * From "SBC-5 Constrained Streams with Data Lifetimes": Device severs
 	 * should assign the lowest numbered stream identifiers to permanent
-- 
2.53.0