linux-kernel - Re: [syzbot] KASAN: out-of-bounds Read in ath9k_hif_usb_rx

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Message-ID: <CACT4Y+atgbwmYmiYqhFQT9_oHw5cD5oyp5bNyCJNz34wSaMgmg@mail.gmail.com>
Date:   Wed, 16 Mar 2022 08:45:28 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     syzbot <syzbot+3f1ca6a6fec34d601788@...kaller.appspotmail.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        ath9k-devel@....qualcomm.com, chouhan.shreyansh630@...il.com,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Kalle Valo <kvalo@...eaurora.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:USB GADGET/PERIPHERAL SUBSYSTEM" 
        <linux-usb@...r.kernel.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Zekun Shen <bruceshenzk@...il.com>
Subject: Re: [syzbot] KASAN: out-of-bounds Read in ath9k_hif_usb_rx_cb (3)

On Tue, 15 Mar 2022 at 18:08, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Tue, Mar 15, 2022 at 2:36 AM syzbot
> <syzbot+3f1ca6a6fec34d601788@...kaller.appspotmail.com> wrote:
> >
> > syzbot suspects this issue was fixed by commit
> > 09688c0166e7 ("Linux 5.17-rc8")
>
> No, I'm afraid that means that the bisection is broken:
>
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=140283ad700000
>
> and yeah, looking at that log it looks like every single run has
>
>   testing commit [...]
>   run #0: crashed: KASAN: use-after-free Read in ath9k_hif_usb_rx_cb
>   ...
>   # git bisect good [...]
>
> and you never saw a "bad" commit that didn't have the issue, so the
> top-of-tree gets marked "good" (and I suspect you intentionally mark
> the broken case "good" in order to find where it got fixed, so you're
> using "git bisect" in a reverse way).
>
> I didn't look closer, but it does seem to not reproduce very reliably,
> maybe that is what confused the bot originally.

Hi Linus,

Thanks for taking a look. Yes, it's a "reverse" bisection that tries
to find the fix.
And your conclusion re flakiness looks right, there were few runs with
only 1/20 crashes.
But the bug looks to be fixed by something anyway. git log on the file
pretty clearly points to:

#syz fix: ath9k: Fix out-of-bound memcpy in ath9k_hif_usb_rx_stream