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From: Oliver Neukum <>
To: Kyungtae Kim <>,
Subject: Re: Fwd: BUG: KASAN: use-after-free in usb_hcd_unlink_urb+0x5f/0x170 drivers/usb/core/hcd.c
Date: Tue, 24 Mar 2020 11:45:53 +0100
Message-ID: <> (raw)
In-Reply-To: <>

Am Montag, den 23.03.2020, 02:18 -0400 schrieb Kyungtae Kim:
> We report a bug (in linux-5.5.11) found by FuzzUSB (a modified version
> of syzkaller)


thank you for the report. Is this a reproducible bug?

> In function usb_hcd_unlink_urb (driver/usb/core/hcd.c:1607), it tries to
> read "urb->use_count". But it seems the instance "urb" was
> already freed (right after urb->dev at line 1597) by the function "urb_destroy"
> in a different thread, which caused memory access violation.


> To solve, it may need to check if urb is valid before urb->use_count,
> to avoid such freed memory access.

Difficult to do as the URB itself would be invalid.

I am afraid there is a race in here:

        if (test_bit(US_FLIDX_ABORTING, &us->dflags)) {
                /* cancel the request, if it hasn't been cancelled already */
                if (test_and_clear_bit(US_FLIDX_SG_ACTIVE, &us->dflags)) {
                        usb_stor_dbg(us, "-- cancelling sg request\n");

        /* wait for the completion of the transfer */
        clear_bit(US_FLIDX_SG_ACTIVE, &us->dflags);

What keeps the request alive while usb_sg_wait() is running?


  reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
2020-03-23  6:18 ` Kyungtae Kim
2020-03-24 10:45   ` Oliver Neukum [this message]
2020-03-24 13:29     ` Alan Stern
2020-03-24 14:14   ` Alan Stern
2020-03-24 14:37     ` Kyungtae Kim
2020-03-26 14:49   ` Alan Stern
2020-03-28 14:11     ` Kyungtae Kim
2020-03-28 15:31       ` Alan Stern
2020-03-28 15:39         ` Kyungtae Kim
2020-03-28 20:18       ` [PATCH] USB: core: Fix free-while-in-use bug in the USB S-Glibrary Alan Stern

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