linux-kernel - Re: KASAN: invalid-free in snd_card

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Date:   Mon, 19 Sep 2022 14:34:36 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Rondreis <linhaoguo86@...il.com>
Cc:     perex@...ex.cz, tiwai@...e.com, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Subject: Re: KASAN: invalid-free in snd_card_new

On Mon, 19 Sep 2022 13:46:43 +0200,
Rondreis wrote:
> 
> Hello,
> 
> I tested this patch with the reproducer and the crash did not trigger again.

Thanks for quick testing.
I'm going to submit and merge the fix, then.


Takashi

> 
> On Mon, Sep 19, 2022 at 5:24 PM Takashi Iwai <tiwai@...e.de> wrote:
> >
> > On Mon, 19 Sep 2022 10:30:54 +0200,
> > Takashi Iwai wrote:
> > >
> > > On Sun, 18 Sep 2022 15:01:11 +0200,
> > > Rondreis wrote:
> > > >
> > > > Hello,
> > > >
> > > > When fuzzing the Linux kernel driver v6.0-rc4, the following crash was
> > > > triggered.
> > > >
> > > > HEAD commit: 7e18e42e4b280c85b76967a9106a13ca61c16179
> > > > git tree: upstream
> > > >
> > > > kernel config: https://pastebin.com/raw/xtrgsXP3
> > > > C reproducer: https://pastebin.com/raw/w2sdQWYj
> > > > console output: https://pastebin.com/raw/Yyf7zw2d
> > > >
> > > > Basically, in the c reproducer, we use the gadget module to emulate
> > > > attaching a USB device(vendor id: 0x1bc7, product id: 0x1206, with the
> > > > midi function) and executing some simple sequence of system calls.
> > > > To reproduce this crash, we utilize a third-party library to emulate
> > > > the attaching process: https://github.com/linux-usb-gadgets/libusbgx.
> > > > Just clone this repository, install it, and compile the c
> > > > reproducer with ``` gcc crash.c -lusbgx -lconfig -o crash ``` will do
> > > > the trick.
> > > >
> > > > I would appreciate it if you have any idea how to solve this bug.
> > >
> > > Could you try the patch below?  It looks like a simple double-free in
> > > the code.
> >
> > A more proper patch is below.  Please give it a try.
> >
> >
> > thanks,
> >
> > Takashi
> >
> > -- 8< --
> > From: Takashi Iwai <tiwai@...e.de>
> > Subject: [PATCH] ALSA: core: Fix double-free at snd_card_new()
> >
> > During the code change to add the support for devres-managed card
> > instance, we put an explicit kfree(card) call at the error path in
> > snd_card_new().  This is needed for the early error path before the
> > card is initialized with the device, but is rather superfluous and
> > causes a double-free at the error path after the card instance is
> > initialized, as the destructor of the card object already contains a
> > kfree() call.
> >
> > This patch fixes the double-free situation by removing the superfluous
> > kfree().  Meanwhile we need to call kfree() explicitly for the early
> > error path, so it's added there instead.
> >
> > Fixes: e8ad415b7a55 ("ALSA: core: Add managed card creation")
> > Reported-by: Rondreis <linhaoguo86@...il.com>
> > Cc: <stable@...r.kernel.org>
> > Link: https://lore.kernel.org/r/CAB7eexL1zBnB636hwS27d-LdPYZ_R1-5fJS_h=ZbCWYU=UPWJg@mail.gmail.com
> > Signed-off-by: Takashi Iwai <tiwai@...e.de>
> > ---
> >  sound/core/init.c | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/sound/core/init.c b/sound/core/init.c
> > index 193dae361fac..5377f94eb211 100644
> > --- a/sound/core/init.c
> > +++ b/sound/core/init.c
> > @@ -178,10 +178,8 @@ int snd_card_new(struct device *parent, int idx, const char *xid,
> >                 return -ENOMEM;
> >
> >         err = snd_card_init(card, parent, idx, xid, module, extra_size);
> > -       if (err < 0) {
> > -               kfree(card);
> > -               return err;
> > -       }
> > +       if (err < 0)
> > +               return err; /* card is freed by error handler */
> >
> >         *card_ret = card;
> >         return 0;
> > @@ -233,7 +231,7 @@ int snd_devm_card_new(struct device *parent, int idx, const char *xid,
> >         card->managed = true;
> >         err = snd_card_init(card, parent, idx, xid, module, extra_size);
> >         if (err < 0) {
> > -               devres_free(card);
> > +               devres_free(card); /* in managed mode, we need to free manually */
> >                 return err;
> >         }
> >
> > @@ -297,6 +295,8 @@ static int snd_card_init(struct snd_card *card, struct device *parent,
> >                 mutex_unlock(&snd_card_mutex);
> >                 dev_err(parent, "cannot find the slot for index %d (range 0-%i), error: %d\n",
> >                          idx, snd_ecards_limit - 1, err);
> > +               if (!card->managed)
> > +                       kfree(card); /* manually free here, as no destructor called */
> >                 return err;
> >         }
> >         set_bit(idx, snd_cards_lock);           /* lock it */
> > --
> > 2.35.3
> >
>