Commit 50901595 authored Oct 16, 2018 by Gustavo A. R. Silva Committed by Greg Kroah-Hartman Nov 10, 2018

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>

parent 89cd15c9

drivers/usb/gadget/function/f_mass_storage.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -221,6 +221,8 @@
		#include <linux/usb/gadget.h>
		#include <linux/usb/composite.h>

		#include <linux/nospec.h>

		#include "configfs.h"


		@@ -3170,6 +3172,7 @@ 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]) {