cdrom: Fix spectre-v1 gadget

This patch fixes a spectre-v1 gadget in cdrom.
The gadget could be triggered by speculatively
bypassing the cdi->capacity check.

Signed-off-by: Jordy Zomer <jordyzomer@google.com>
Link: https://lore.kernel.org/all/20230612110040.849318-2-jordyzomer@google.com
Reviewed-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/all/ZI1+1OG9Ut1MqsUC@equinox
Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20230617113828.1230-2-phil@philpotter.co.uk
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
index bd8cd59..cc28398 100644 (file)
--- a/drivers/cdrom/cdrom.c
+++ b/drivers/cdrom/cdrom.c
@@ -264,6 +264,7 @@
 #include <linux/errno.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
+#include <linux/nospec.h>
 #include <linux/slab.h> 
 #include <linux/cdrom.h>
 #include <linux/sysctl.h>
@@ -2311,6 +2312,9 @@ static int cdrom_ioctl_media_changed(struct cdrom_device_info *cdi,
        if (arg >= cdi->capacity)
                return -EINVAL;
 
+       /* Prevent arg from speculatively bypassing the length check */
+       barrier_nospec();
+
        info = kmalloc(sizeof(*info), GFP_KERNEL);
        if (!info)
                return -ENOMEM;