linux-kernel - Re: [syzbot] KASAN: slab-out-of-bounds Write in usb_hcd_poll_rh

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Date:   Thu, 30 Dec 2021 21:31:29 -0500
From:   Alan Stern <stern@...land.harvard.edu>
To:     syzbot <syzbot+3ae6a2b06f131ab9849f@...kaller.appspotmail.com>
Cc:     andreyknvl@...gle.com, dvyukov@...gle.com,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: slab-out-of-bounds Write in
 usb_hcd_poll_rh_status (2)

[Trimmed CC: list]

On Thu, Dec 30, 2021 at 04:49:18PM -0800, syzbot wrote:
> Hello,
> 
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> KASAN: slab-out-of-bounds Write in usb_hcd_poll_rh_status
...
> Tested on:
> 
> commit:         eec4df26 Merge tag 's390-5.16-6' of git://git.kernel.o..
> git tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/

I'm glad to see that the git tree is reported properly, but the commit 
label is too short.  The reproducer bug report had exactly the opposite 
problems!  It said:

> syzbot has found a reproducer for the following issue on:
>
> HEAD commit:    eec4df26e24e Merge tag 's390-5.16-6' of git://git.kernel.o..
> git tree:       upstream

Andrey or Dmitry?  Can you guys unify these two outputs to make both 
lines correct always?

Moving on...  Important lines from the console log:

[   76.919138][ T4081] usb usb9: usbdev_do_ioctl: BULK
[   76.924966][ T4081] usb usb9: usbfs: process 4081 (syz-executor189) did not claim interface 0 before use
[   76.935186][ T4081] usb usb9: ep1 int-in, length 1, timeout 9
[   76.941355][ T4099] usb usb9: opened by process 4099: syz-executor189
[   76.942606][ T4087] usb usb9: usbdev_do_ioctl: BULK
[   76.949968][    C1] 
==================================================================
[   76.950070][    C1] BUG: KASAN: slab-out-of-bounds in usb_hcd_poll_rh_status+0x376/0x780
[   76.950102][    C1] Write of size 2 at addr ffff8880121ae230 by task syz-executor189/4087

It's hard to tell what's really happening.  The suspicious part is the 
"length 1" combined with the "Write of size 2" -- but they refer to 
different processes!

Maybe this diagnostic patch will help a little.

Alan Stern

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/ eec4df26e24e

Index: usb-devel/drivers/usb/core/devio.c
===================================================================
--- usb-devel.orig/drivers/usb/core/devio.c
+++ usb-devel/drivers/usb/core/devio.c
@@ -109,7 +109,7 @@ struct async {
 	u8 bulk_status;
 };
 
-static bool usbfs_snoop;
+static bool usbfs_snoop = true;
 module_param(usbfs_snoop, bool, S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(usbfs_snoop, "true to log all usbfs traffic");
 
Index: usb-devel/drivers/usb/core/hcd.c
===================================================================
--- usb-devel.orig/drivers/usb/core/hcd.c
+++ usb-devel/drivers/usb/core/hcd.c
@@ -809,8 +809,10 @@ static int rh_queue_status (struct usb_h
 	unsigned	len = 1 + (urb->dev->maxchild / 8);
 
 	spin_lock_irqsave (&hcd_root_hub_lock, flags);
+	dev_info(hcd->self.controller, "rh_queue_status: len %d tblen %d\n",
+			len, urb->transfer_buffer_length);
 	if (hcd->status_urb || urb->transfer_buffer_length < len) {
-		dev_dbg (hcd->self.controller, "not queuing rh status urb\n");
+		dev_info(hcd->self.controller, "not queuing rh status urb\n");
 		retval = -EINVAL;
 		goto done;
 	}