[SRU][Bionic][PATCH 1/1] sr: pass down correctly sized SCSI sense buffer

[Kleber Sacilotto de Souza]

From: Jens Axboe <axboe at kernel.dk>

We're casting the CDROM layer request_sense to the SCSI sense
buffer, but the former is 64 bytes and the latter is 96 bytes.
As we generally allocate these on the stack, we end up blowing
up the stack.

Fix this by wrapping the scsi_execute() call with a properly
sized sense buffer, and copying back the bits for the CDROM
layer.

Cc: stable at vger.kernel.org
Reported-by: Piotr Gabriel Kosinski <pg.kosinski at gmail.com>
Reported-by: Daniel Shapira <daniel at twistlock.com>
Tested-by: Kees Cook <keescook at chromium.org>
Fixes: 82ed4db499b8 ("block: split scsi_request out of struct request")
Signed-off-by: Jens Axboe <axboe at kernel.dk>

CVE-2018-11506
(cherry picked from commit f7068114d45ec55996b9040e98111afa56e010fe)
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
---
 drivers/scsi/sr_ioctl.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/sr_ioctl.c b/drivers/scsi/sr_ioctl.c
index 2a21f2d48592..35fab1e18adc 100644
--- a/drivers/scsi/sr_ioctl.c
+++ b/drivers/scsi/sr_ioctl.c
@@ -188,9 +188,13 @@ int sr_do_ioctl(Scsi_CD *cd, struct packet_command *cgc)
 	struct scsi_device *SDev;
 	struct scsi_sense_hdr sshdr;
 	int result, err = 0, retries = 0;
+	unsigned char sense_buffer[SCSI_SENSE_BUFFERSIZE], *senseptr = NULL;
 
 	SDev = cd->device;
 
+	if (cgc->sense)
+		senseptr = sense_buffer;
+
       retry:
 	if (!scsi_block_when_processing_errors(SDev)) {
 		err = -ENODEV;
@@ -198,10 +202,12 @@ int sr_do_ioctl(Scsi_CD *cd, struct packet_command *cgc)
 	}
 
 	result = scsi_execute(SDev, cgc->cmd, cgc->data_direction,
-			      cgc->buffer, cgc->buflen,
-			      (unsigned char *)cgc->sense, &sshdr,
+			      cgc->buffer, cgc->buflen, senseptr, &sshdr,
 			      cgc->timeout, IOCTL_RETRIES, 0, 0, NULL);
 
+	if (cgc->sense)
+		memcpy(cgc->sense, sense_buffer, sizeof(*cgc->sense));
+
 	/* Minimal error checking.  Ignore cases we know about, and report the rest. */
 	if (driver_byte(result) != 0) {
 		switch (sshdr.sense_key) {
-- 
2.17.1