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Date:   Mon, 10 Aug 2020 18:37:17 +0200
From:   Pavel Machek <pavel@denx.de>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        syzbot+1a54a94bd32716796edd@syzkaller.appspotmail.com,
        syzbot+9d2abfef257f3e2d4713@syzkaller.appspotmail.com,
        Hillf Danton <hdanton@sina.com>, Takashi Iwai <tiwai@suse.de>
Subject: Re: [PATCH 4.19 06/48] ALSA: seq: oss: Serialize ioctls
Message-ID: <20200810163717.GA24408@amd>
References: <20200810151804.199494191@linuxfoundation.org>
 <20200810151804.528955642@linuxfoundation.org>
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Hi!

> commit 80982c7e834e5d4e325b6ce33757012ecafdf0bb upstream.
>=20
> Some ioctls via OSS sequencer API may race and lead to UAF when the
> port create and delete are performed concurrently, as spotted by a
> couple of syzkaller cases.  This patch is an attempt to address it by
> serializing the ioctls with the existing register_mutex.
>=20
> Basically OSS sequencer API is an obsoleted interface and was designed
> without much consideration of the concurrency.  There are very few
> applications with it, and the concurrent performance isn't asked,
> hence this "big hammer" approach should be good enough.

That really is a "big hammer". And I believe it is too big.

In particular, do we need to drop the lock while sleeping in
SNDCTL_SEQ_SYNC: =3D> snd_seq_oss_writeq_sync ?

Best regards,
								Pavel
--=20
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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