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Date:   Fri, 29 Oct 2021 09:53:28 -0400
From:   Zekun Shen <bruceshenzk@gmail.com>
To:     Kalle Valo <kvalo@codeaurora.org>
Cc:     Pontus Fuchs <pontus.fuchs@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] ar5523: Fix null-ptr-deref with unexpected
 WDCMSG_TARGET_START  =?ISO-8859-1?Q?=20reply=1B?=
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On Fri, Oct 29, 2021 at 06:53:30AM +0300, Kalle Valo wrote:
> Zekun Shen <bruceshenzk@gmail.com> writes:
> 
> > Unexpected WDCMSG_TARGET_START replay can lead to null-ptr-deref
> > when ar->tx_cmd->odata is NULL. The patch adds a null check to
> > prevent such case.
> >
> > KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> >  ar5523_cmd+0x46a/0x581 [ar5523]
> >  ar5523_probe.cold+0x1b7/0x18da [ar5523]
> >  ? ar5523_cmd_rx_cb+0x7a0/0x7a0 [ar5523]
> >  ? __pm_runtime_set_status+0x54a/0x8f0
> >  ? _raw_spin_trylock_bh+0x120/0x120
> >  ? pm_runtime_barrier+0x220/0x220
> >  ? __pm_runtime_resume+0xb1/0xf0
> >  usb_probe_interface+0x25b/0x710
> >  really_probe+0x209/0x5d0
> >  driver_probe_device+0xc6/0x1b0
> >  device_driver_attach+0xe2/0x120
> >
> > Signed-off-by: Zekun Shen <bruceshenzk@gmail.com>
> 
> How did you test this?
I found the bug using a custome USBFuzz port. It's a research work
to fuzz USB stack/drivers. I modified it to fuzz ath9k driver only,
providing hand-crafted usb descriptors to QEMU.

After fixing the code (fourth byte in usb packet) to WDCMSG_TARGET_START, 
I got the null-ptr-deref bug. I believe the bug is triggerable whenever
cmd->odata is NULL. After patching, I tested with the same input and no
longer see the KASAN report.
> 
> -- 
> https://patchwork.kernel.org/project/linux-wireless/list/
> 
> https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches