[PATCH 3.12 073/170] usb: gadget: f_fs: fix NULL pointer dereference when there are no strings

Jiri Slaby
2014-07-18T13:10:22Z

From: Michal Nazarewicz <mina86@mina86.com>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

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@mina86.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
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 44cf775a8627..c3067f4f213a 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;
--
2.0.0