linux-kernel - [PATCH v2] pktcdvd: Fix possible Spectre-v1 for pkt

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Date:   Sat, 28 Jul 2018 11:30:58 +0900
From:   Jinbum Park <jinb.park7@...il.com>
To:     axboe@...nel.dk, bart.vanassche@....com,
        jiufei.xue@...ux.alibaba.com
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        gustavo@...eddedor.com
Subject: [PATCH v2] pktcdvd: Fix possible Spectre-v1 for pkt_devs

User controls @dev_minor which to be used as index of pkt_devs.
So, It can be exploited via Spectre-like attack. (speculative execution)

This kind of attack leaks address of pkt_devs, [1]
It leads an attacker to bypass security mechanism such as KASLR.

So sanitize @dev_minor before using it to prevent attack.

[1] https://github.com/jinb-park/linux-exploit/
tree/master/exploit-remaining-spectre-gadget/leak_pkt_devs.c

Signed-off-by: Jinbum Park <jinb.park7@...il.com>
---
v2: Fix coding style by Gustavo.

 drivers/block/pktcdvd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/block/pktcdvd.c b/drivers/block/pktcdvd.c
index c61d20c..8ec2eaa 100644
--- a/drivers/block/pktcdvd.c
+++ b/drivers/block/pktcdvd.c
@@ -67,8 +67,8 @@
 #include <scsi/scsi.h>
 #include <linux/debugfs.h>
 #include <linux/device.h>
-
 #include <linux/uaccess.h>
+#include <linux/nospec.h>
 
 #define DRIVER_NAME	"pktcdvd"
 
@@ -2231,6 +2231,7 @@ static struct pktcdvd_device *pkt_find_dev_from_minor(unsigned int dev_minor)
 {
 	if (dev_minor >= MAX_WRITERS)
 		return NULL;
+	dev_minor = array_index_nospec(dev_minor, MAX_WRITERS);
 	return pkt_devs[dev_minor];
 }
 
-- 
1.9.1