ata: libata-sff: Ensure that we cannot write outside the allocated buffer

reveliofuzzing reported that a SCSI_IOCTL_SEND_COMMAND ioctl with out_len
set to 0xd42, SCSI command set to ATA_16 PASS-THROUGH, ATA command set to
ATA_NOP, and protocol set to ATA_PROT_PIO, can cause ata_pio_sector() to
write outside the allocated buffer, overwriting random memory.

While a ATA device is supposed to abort a ATA_NOP command, there does seem
to be a bug either in libata-sff or QEMU, where either this status is not
set, or the status is cleared before read by ata_sff_hsm_move().
Anyway, that is most likely a separate bug.

Looking at __atapi_pio_bytes(), it already has a safety check to ensure
that __atapi_pio_bytes() cannot write outside the allocated buffer.

Add a similar check to ata_pio_sector(), such that also ata_pio_sector()
cannot write outside the allocated buffer.

Cc: stable@vger.kernel.org
Reported-by: reveliofuzzing <reveliofuzzing@gmail.com>
Closes: https://lore.kernel.org/linux-ide/CA+-ZZ_jTgxh3bS7m+KX07_EWckSnW3N2adX3KV63y4g7M4CZ2A@mail.gmail.com/
Link: https://lore.kernel.org/r/20250127154303.15567-2-cassel@kernel.org
Signed-off-by: Niklas Cassel <cassel@kernel.org>

Author: floatious

drivers/ata/libata-sff.c

@@ -601,7 +601,7 @@ static void ata_pio_sector(struct ata_queued_cmd *qc)
 {
 	struct ata_port *ap = qc->ap;
 	struct page *page;
-	unsigned int offset;
+	unsigned int offset, count;
 
 	if (!qc->cursg) {
 		qc->curbytes = qc->nbytes;
@@ -617,25 +617,27 @@ static void ata_pio_sector(struct ata_queued_cmd *qc)
 	page = nth_page(page, (offset >> PAGE_SHIFT));
 	offset %= PAGE_SIZE;
 
-	trace_ata_sff_pio_transfer_data(qc, offset, qc->sect_size);
+	/* don't overrun current sg */
+	count = min(qc->cursg->length - qc->cursg_ofs, qc->sect_size);
+
+	trace_ata_sff_pio_transfer_data(qc, offset, count);
 
 	/*
 	 * Split the transfer when it splits a page boundary.  Note that the
 	 * split still has to be dword aligned like all ATA data transfers.
 	 */
 	WARN_ON_ONCE(offset % 4);
-	if (offset + qc->sect_size > PAGE_SIZE) {
+	if (offset + count > PAGE_SIZE) {
 		unsigned int split_len = PAGE_SIZE - offset;
 
 		ata_pio_xfer(qc, page, offset, split_len);
-		ata_pio_xfer(qc, nth_page(page, 1), 0,
-			     qc->sect_size - split_len);
+		ata_pio_xfer(qc, nth_page(page, 1), 0, count - split_len);
 	} else {
-		ata_pio_xfer(qc, page, offset, qc->sect_size);
+		ata_pio_xfer(qc, page, offset, count);
 	}
 
-	qc->curbytes += qc->sect_size;
-	qc->cursg_ofs += qc->sect_size;
+	qc->curbytes += count;
+	qc->cursg_ofs += count;
 
 	if (qc->cursg_ofs == qc->cursg->length) {
 		qc->cursg = sg_next(qc->cursg);