Patch "USB: uas: fix bug in handling of alternate settings" has been added to the 3.18-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    USB: uas: fix bug in handling of alternate settings

to the 3.18-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     usb-uas-fix-bug-in-handling-of-alternate-settings.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 786de92b3cb26012d3d0f00ee37adf14527f35c4 Mon Sep 17 00:00:00 2001
From: Alan Stern <stern@rowland.harvard.edu>
Date: Fri, 22 Sep 2017 11:56:49 -0400
Subject: USB: uas: fix bug in handling of alternate settings

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

commit 786de92b3cb26012d3d0f00ee37adf14527f35c4 upstream.

The uas driver has a subtle bug in the way it handles alternate
settings.  The uas_find_uas_alt_setting() routine returns an
altsetting value (the bAlternateSetting number in the descriptor), but
uas_use_uas_driver() then treats that value as an index to the
intf->altsetting array, which it isn't.

Normally this doesn't cause any problems because the various
alternate settings have bAlternateSetting values 0, 1, 2, ..., so the
value is equal to the index in the array.  But this is not guaranteed,
and Andrey Konovalov used the syzkaller fuzzer with KASAN to get a
slab-out-of-bounds error by violating this assumption.

This patch fixes the bug by making uas_find_uas_alt_setting() return a
pointer to the altsetting entry rather than either the value or the
index.  Pointers are less subject to misinterpretation.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
CC: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/usb/storage/uas-detect.h |   15 ++++++++-------
 drivers/usb/storage/uas.c        |   10 +++++-----
 2 files changed, 13 insertions(+), 12 deletions(-)

--- a/drivers/usb/storage/uas-detect.h
+++ b/drivers/usb/storage/uas-detect.h
@@ -9,7 +9,8 @@ static int uas_is_interface(struct usb_h
 		intf->desc.bInterfaceProtocol == USB_PR_UAS);
 }
 
-static int uas_find_uas_alt_setting(struct usb_interface *intf)
+static struct usb_host_interface *uas_find_uas_alt_setting(
+		struct usb_interface *intf)
 {
 	int i;
 
@@ -17,10 +18,10 @@ static int uas_find_uas_alt_setting(stru
 		struct usb_host_interface *alt = &intf->altsetting[i];
 
 		if (uas_is_interface(alt))
-			return alt->desc.bAlternateSetting;
+			return alt;
 	}
 
-	return -ENODEV;
+	return NULL;
 }
 
 static int uas_find_endpoints(struct usb_host_interface *alt,
@@ -58,14 +59,14 @@ static int uas_use_uas_driver(struct usb
 	struct usb_device *udev = interface_to_usbdev(intf);
 	struct usb_hcd *hcd = bus_to_hcd(udev->bus);
 	unsigned long flags = id->driver_info;
-	int r, alt;
-
+	struct usb_host_interface *alt;
+	int r;
 
 	alt = uas_find_uas_alt_setting(intf);
-	if (alt < 0)
+	if (!alt)
 		return 0;
 
-	r = uas_find_endpoints(&intf->altsetting[alt], eps);
+	r = uas_find_endpoints(alt, eps);
 	if (r < 0)
 		return 0;
 
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -866,14 +866,14 @@ MODULE_DEVICE_TABLE(usb, uas_usb_ids);
 static int uas_switch_interface(struct usb_device *udev,
 				struct usb_interface *intf)
 {
-	int alt;
+	struct usb_host_interface *alt;
 
 	alt = uas_find_uas_alt_setting(intf);
-	if (alt < 0)
-		return alt;
+	if (!alt)
+		return -ENODEV;
 
-	return usb_set_interface(udev,
-			intf->altsetting[0].desc.bInterfaceNumber, alt);
+	return usb_set_interface(udev, alt->desc.bInterfaceNumber,
+			alt->desc.bAlternateSetting);
 }
 
 static int uas_configure_endpoints(struct uas_dev_info *devinfo)


Patches currently in stable-queue which might be from stern@rowland.harvard.edu are

queue-3.18/usb-uas-fix-bug-in-handling-of-alternate-settings.patch
queue-3.18/usb-dummy-hcd-fix-infinite-loop-resubmission-bug.patch
queue-3.18/usb-storage-unusual_devs-entry-to-fix-write-access-regression-for-seagate-external-drives.patch
queue-3.18/usb-gadgetfs-fix-copy_to_user-while-holding-spinlock.patch
queue-3.18/usb-devio-don-t-corrupt-user-memory.patch
queue-3.18/usb-gadgetfs-fix-crash-caused-by-inadequate-synchronization.patch
queue-3.18/usb-dummy-hcd-fix-connection-failures-wrong-speed.patch