[PATCH] usb: gadget: midi2: prevent in/out jack from oob

[Edward Adam Davis <eadavis@sina.com>]

The increment of config->jack_out in append_midi1_out_jack() lacked
bounds checking, triggering issue [1] when the value approached the
limit MAX_CABLES.

A similar out-of-bounds issue exists in append_midi1_in_jack(), so it
is being fixed as well.

Before incrementing jack_out/in, the code now checks if the value has
reached the upper limit MAX_CABLES; if so, it exits and returns -EINVAL.

Additionally, the jack_id assignment is moved to occur after the jack_out
bounds check to prevent wasting IDs on invalid increments.

[1]
BUG: KASAN: stack-out-of-bounds in append_midi1_out_jack.isra.0+0x38c/0x470 drivers/usb/gadget/function/f_midi2.c:1713
Write of size 1 at addr ffffc90003277880 by task syz-executor119/6000
Call Trace:
 append_midi1_out_jack.isra.0+0x38c/0x470 drivers/usb/gadget/function/f_midi2.c:1713
 f_midi2_create_usb_configs+0x748/0xdf0 drivers/usb/gadget/function/f_midi2.c:1815
 f_midi2_bind+0x1d12/0x2770 drivers/usb/gadget/function/f_midi2.c:2013
 usb_add_function+0x219/0x890 drivers/usb/gadget/composite.c:333
 configfs_composite_bind+0xd83/0x1960 drivers/usb/gadget/configfs.c:1802
 gadget_bind_driver+0x28c/0xbf0 drivers/usb/gadget/udc/core.c:1662
 call_driver_probe drivers/base/dd.c:628 [inline]
 really_probe+0x241/0xa60 drivers/base/dd.c:706
 
Fixes: 856fa444b098 ("usb: gadget: midi2: Dynamically create MIDI 1.0 altset descriptors")
Reported-by: syzbot+c35f34092a4bc9855be6@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c35f34092a4bc9855be6
Tested-by: syzbot+c35f34092a4bc9855be6@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@sina.com>
---
 drivers/usb/gadget/function/f_midi2.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/gadget/function/f_midi2.c b/drivers/usb/gadget/function/f_midi2.c
index 19fdac024343..06a3add05447 100644
--- a/drivers/usb/gadget/function/f_midi2.c
+++ b/drivers/usb/gadget/function/f_midi2.c
@@ -1675,11 +1675,15 @@ static int append_midi1_in_jack(struct f_midi2 *midi2,
 				struct midi1_cable_mapping *map,
 				unsigned int type)
 {
-	struct usb_midi_in_jack_descriptor *jack =
-		&config->jack_ins[config->jack_in++];
-	int id = ++config->jack_id;
+	struct usb_midi_in_jack_descriptor *jack;
+	int id;
 	int err;
 
+	if (config->jack_in >= MAX_CABLES)
+		return -EINVAL;
+
+	id = ++config->jack_id;
+	jack = &config->jack_ins[config->jack_in++];
 	jack->bLength = 0x06;
 	jack->bDescriptorType = USB_DT_CS_INTERFACE;
 	jack->bDescriptorSubtype = USB_MS_MIDI_IN_JACK;
@@ -1700,11 +1704,15 @@ static int append_midi1_out_jack(struct f_midi2 *midi2,
 				 struct midi1_cable_mapping *map,
 				 unsigned int type, unsigned int source)
 {
-	struct usb_midi_out_jack_descriptor_1 *jack =
-		&config->jack_outs[config->jack_out++];
-	int id = ++config->jack_id;
+	struct usb_midi_out_jack_descriptor_1 *jack;
+	int id;
 	int err;
 
+	if (config->jack_out >= MAX_CABLES)
+		return -EINVAL;
+
+	id = ++config->jack_id;
+	jack = &config->jack_outs[config->jack_out++];
 	jack->bLength = 0x09;
 	jack->bDescriptorType = USB_DT_CS_INTERFACE;
 	jack->bDescriptorSubtype = USB_MS_MIDI_OUT_JACK;
-- 
2.43.0