libata: reject passthrough WRITE SAME requests

The WRITE SAME to TRIM translation rewrites the DATA OUT buffer.  While
the SCSI code accomodates for this by passing a read-writable buffer
userspace applications don't cater for this behavior.  In fact it can
be used to rewrite e.g. a readonly file through mmap and should be
considered as a security fix.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

drivers/ata/libata-scsi.c

@@ -3462,6 +3462,14 @@ static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
 	if (unlikely(!dev->dma_mode))
 		goto invalid_opcode;
 
+	/*
+	 * We only allow sending this command through the block layer,
+	 * as it modifies the DATA OUT buffer, which would corrupt user
+	 * memory for SG_IO commands.
+	 */
+	if (unlikely(blk_rq_is_passthrough(scmd->request)))
+		goto invalid_opcode;
+
 	if (unlikely(scmd->cmd_len < 16)) {
 		fp = 15;
 		goto invalid_fld;