Hi Jinbum, Thanks for working on this. Please, see some comments below. On 07/27/2018 08:31 PM, Jinbum Park wrote: > 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@xxxxxxxxx> > --- > drivers/block/pktcdvd.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/drivers/block/pktcdvd.c b/drivers/block/pktcdvd.c > index c61d20c..665760d 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" > > @@ -2229,9 +2229,13 @@ static void pkt_release_dev(struct pktcdvd_device *pd, int flush) > > static struct pktcdvd_device *pkt_find_dev_from_minor(unsigned int dev_minor) > { > + unsigned int idx = 0; > + There is no need for a new variable in this case. > if (dev_minor >= MAX_WRITERS) > return NULL; > - return pkt_devs[dev_minor]; > + > + idx = array_index_nospec(dev_minor, MAX_WRITERS); > + return pkt_devs[idx]; Also, the following style is preferred: if (dev_minor >= MAX_WRITERS) return NULL; dev_minor = array_index_nospec(dev_minor, MAX_WRITERS); Thanks -- Gustavo
