From: Gustavo A. R. Silva <gustavo@embeddedor.com>
Date: Tue, 16 Oct 2018 10:16:45 +0000 (+0200)
Subject: usb: gadget: storage: Fix Spectre v1 vulnerability
X-Git-Tag: v4.9.136~8
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=4121be5950ead355c4c3e08543f585e9e7100a20;p=platform%2Fkernel%2Flinux-amlogic.git

usb: gadget: storage: Fix Spectre v1 vulnerability

commit 9ae24af3669111d418242caec8dd4ebd9ba26860 upstream.

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>
Acked-by: Felipe Balbi <felipe.balbi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/usb/gadget/function/f_mass_storage.c b/drivers/usb/gadget/function/f_mass_storage.c
index d2fc237cd87a..fac9424940d4 100644
--- a/drivers/usb/gadget/function/f_mass_storage.c
+++ b/drivers/usb/gadget/function/f_mass_storage.c
@@ -220,6 +220,8 @@
 #include <linux/usb/gadget.h>
 #include <linux/usb/composite.h>
 
+#include <linux/nospec.h>
+
 #include "configfs.h"
 
 
@@ -3260,6 +3262,7 @@ 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]) {