[PATCH] usb: gadget: storage: Fix Spectre v1 vulnerability

[PATCH] usb: gadget: storage: Fix Spectre v1 vulnerability

[Gustavo A. R. Silva]

num can be indirectly controlled by user-space, hence leading to
a potential exploitation of the Spectre variant 1 vulnerability.

This issue was detected with the help of Smatch:

drivers/usb/gadget/function/f_mass_storage.c:3177 fsg_lun_make() warn:
potential spectre issue 'fsg_opts->common->luns' [r] (local cap)

Fix this by sanitizing num before using it to index
fsg_opts->common->luns

Notice that given that speculation windows are large, the policy is
to kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

Cc: stable@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 drivers/usb/gadget/function/f_mass_storage.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/usb/gadget/function/f_mass_storage.c b/drivers/usb/gadget/function/f_mass_storage.c
index cb402e7a..043f97a 100644
--- a/drivers/usb/gadget/function/f_mass_storage.c
+++ b/drivers/usb/gadget/function/f_mass_storage.c
@@ -221,6 +221,8 @@
 #include <linux/usb/gadget.h>
 #include <linux/usb/composite.h>
 
+#include <linux/nospec.h>
+
 #include "configfs.h"
 
 
@@ -3152,6 +3154,7 @@ static struct config_group *fsg_lun_make(struct config_group *group,
 	fsg_opts = to_fsg_opts(&group->cg_item);
 	if (num >= FSG_MAX_LUNS)
 		return ERR_PTR(-ERANGE);
+	num = array_index_nospec(num, FSG_MAX_LUNS);
 
 	mutex_lock(&fsg_opts->lock);
 	if (fsg_opts->refcnt || fsg_opts->common->luns[num]) {
-- 
2.7.4

Re: [PATCH] usb: gadget: storage: Fix Spectre v1 vulnerability

[Felipe Balbi]

Hi Greg,

"Gustavo A. R. Silva" <gustavo@embeddedor.com> writes:

> num can be indirectly controlled by user-space, hence leading to
> a potential exploitation of the Spectre variant 1 vulnerability.
>
> This issue was detected with the help of Smatch:
>
> drivers/usb/gadget/function/f_mass_storage.c:3177 fsg_lun_make() warn:
> potential spectre issue 'fsg_opts->common->luns' [r] (local cap)
>
> Fix this by sanitizing num before using it to index
> fsg_opts->common->luns
>
> Notice that given that speculation windows are large, the policy is
> to kill the speculation on the first load and not worry if it can be
> completed with a dependent load/store [1].
>
> [1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

Can you still take this as an urgent fix?

Acked-by: Felipe Balbi <felipe.balbi@intel.com>

-- 
balbi

Re: [PATCH] usb: gadget: storage: Fix Spectre v1 vulnerability

[Greg Kroah-Hartman]

On Tue, Oct 16, 2018 at 02:28:19PM +0300, Felipe Balbi wrote:
> 
> Hi Greg,
> 
> "Gustavo A. R. Silva" <gustavo@embeddedor.com> writes:
> 
> > num can be indirectly controlled by user-space, hence leading to
> > a potential exploitation of the Spectre variant 1 vulnerability.
> >
> > This issue was detected with the help of Smatch:
> >
> > drivers/usb/gadget/function/f_mass_storage.c:3177 fsg_lun_make() warn:
> > potential spectre issue 'fsg_opts->common->luns' [r] (local cap)
> >
> > Fix this by sanitizing num before using it to index
> > fsg_opts->common->luns
> >
> > Notice that given that speculation windows are large, the policy is
> > to kill the speculation on the first load and not worry if it can be
> > completed with a dependent load/store [1].
> >
> > [1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2
> >
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> 
> Can you still take this as an urgent fix?
> 
> Acked-by: Felipe Balbi <felipe.balbi@intel.com>

Yes, will do so, thanks.

greg k-h

> 
> -- 
> balbi