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

Ben Hutchings
2017-08-18T13:15:50Z

From: Christoph Hellwig <hch@lst.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@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Tejun Heo <tj@kernel.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@decadent.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);