[PATCH] libata: reject passthrough WRITE SAME requests

[PATCH] libata: reject passthrough WRITE SAME requests

[Christoph Hellwig]

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
---
 drivers/ata/libata-scsi.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 1ac70744ae7b..50f56d066936 100644
--- a/drivers/ata/libata-scsi.c
+++ b/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;
-- 
2.11.0

Re: [PATCH] libata: reject passthrough WRITE SAME requests

[Martin K. Petersen]

Christoph,

> 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.

Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: [PATCH] libata: reject passthrough WRITE SAME requests

[Tejun Heo]

On Tue, Apr 25, 2017 at 01:39:54PM +0200, Christoph Hellwig wrote:
> 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

Applied to libata/for-4.12, assuming we aren't doing rc9.

Thanks.

-- 
tejun