linux-kernel - [PATCH 3.16 092/134] libata: reject passthrough WRITE SAME requests

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Message-ID: <lsq.1503062000.121644328@decadent.org.uk>
Date:   Fri, 18 Aug 2017 14:13:20 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Tejun Heo" <tj@...nel.org>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "Christoph Hellwig" <hch@....de>
Subject: [PATCH 3.16 092/134] libata: reject passthrough WRITE SAME requests

3.16.47-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Christoph Hellwig <hch@....de>

commit c6ade20f5e50e188d20b711a618b20dd1d50457e upstream.

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@....de>
Reviewed-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Tejun Heo <tj@...nel.org>
[bwh: Backported to 3.16:
 - Open-code blk_rq_is_passthrough()
 - We don't distinguish which field is invaid so goto invalid_fld
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/ata/libata-scsi.c | 8 ++++++++
 1 file changed, 8 insertions(+)

--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -3097,6 +3097,14 @@ static unsigned int ata_scsi_write_same_
 	if (unlikely(!dev->dma_mode))
 		goto invalid_fld;
 
+	/*
+	 * 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(scmd->request->cmd_type != REQ_TYPE_FS))
+		goto invalid_fld;
+
 	if (unlikely(scmd->cmd_len < 16))
 		goto invalid_fld;
 	scsi_16_lba_len(cdb, &block, &n_block);