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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org,
        "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
        "Alan Stern" <stern@rowland.harvard.edu>,
        syzbot+19c3aaef85a89d451eac@syzkaller.appspotmail.com
Date:   Sun, 09 Dec 2018 21:50:33 +0000
Message-ID: <lsq.1544392233.502563245@decadent.org.uk>
Subject: [PATCH 3.16 256/328] USB: handle NULL config in usb_find_alt_setting()
In-Reply-To: <lsq.1544392232.713909046@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
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3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Alan Stern <stern@rowland.harvard.edu>

commit c9a4cb204e9eb7fa7dfbe3f7d3a674fa530aa193 upstream.

usb_find_alt_setting() takes a pointer to a struct usb_host_config as
an argument; it searches for an interface with specified interface and
alternate setting numbers in that config.  However, it crashes if the
usb_host_config pointer argument is NULL.

Since this is a general-purpose routine, available for use in many
places, we want to to be more robust.  This patch makes it return NULL
whenever the config argument is NULL.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: syzbot+19c3aaef85a89d451eac@syzkaller.appspotmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 drivers/usb/core/usb.c | 2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/usb/core/usb.c
+++ b/drivers/usb/core/usb.c
@@ -79,6 +79,8 @@ struct usb_host_interface *usb_find_alt_
 	struct usb_interface_cache *intf_cache = NULL;
 	int i;
 
+	if (!config)
+		return NULL;
 	for (i = 0; i < config->desc.bNumInterfaces; i++) {
 		if (config->intf_cache[i]->altsetting[0].desc.bInterfaceNumber
 				== iface_num) {