[3.11.y.z extended stable] Patch "usb: gadget: f_fs: fix NULL pointer dereference when there are no strings" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    usb: gadget: f_fs: fix NULL pointer dereference when there are no strings

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From ad4204b65ecf6ecd2f736fffb30a33f9d9065651 Mon Sep 17 00:00:00 2001
From: Michal Nazarewicz <mina86 at mina86.com>
Date: Tue, 17 Jun 2014 17:47:41 +0200
Subject: usb: gadget: f_fs: fix NULL pointer dereference when there are no
 strings
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

commit f0688c8b81d2ea239c3fb0b848f623b579238d99 upstream.

If the descriptors do not need any strings and user space sends empty
set of strings, the ffs->stringtabs field remains NULL.  Thus
*ffs->stringtabs in functionfs_bind leads to a NULL pointer
dereferenece.

The bug was introduced by commit [fd7c9a007f: “use usb_string_ids_n()”].

While at it, remove double initialisation of lang local variable in
that function.

ffs->strings_count does not need to be checked in any way since in
the above scenario it will remain zero and usb_string_ids_n() is
a no-operation when colled with 0 argument.

Signed-off-by: Michal Nazarewicz <mina86 at mina86.com>
Signed-off-by: Felipe Balbi <balbi at ti.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/usb/gadget/f_fs.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/gadget/f_fs.c b/drivers/usb/gadget/f_fs.c
index b6e9d917221e..84219f656051 100644
--- a/drivers/usb/gadget/f_fs.c
+++ b/drivers/usb/gadget/f_fs.c
@@ -1389,11 +1389,13 @@ static int functionfs_bind(struct ffs_data *ffs, struct usb_composite_dev *cdev)
 	ffs->ep0req->context = ffs;

 	lang = ffs->stringtabs;
-	for (lang = ffs->stringtabs; *lang; ++lang) {
-		struct usb_string *str = (*lang)->strings;
-		int id = first_id;
-		for (; str->s; ++id, ++str)
-			str->id = id;
+	if (lang) {
+		for (; *lang; ++lang) {
+			struct usb_string *str = (*lang)->strings;
+			int id = first_id;
+			for (; str->s; ++id, ++str)
+				str->id = id;
+		}
 	}

 	ffs->gadget = cdev->gadget;
--
1.9.1