From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794540248; b=XGXaEqBfkeHTrsljvhsOltgmbxqgSgIBgWi+K3Lci+2jTaUavQyLvPxs89z4RstOUbSf zJuRRQuS0fHoe6SaTC0kllcO1/FuEuRzV1kwUsSUhyfbzRfWxQco6cP9xlcrlMKkfJYCD AMFWMUixCXxsS4bq3f6Ai8Hlx1/YwQAiKpRd02O9AqiHdWZzhVStYgBXhJoaynRlZRKoL poXOeCza75qLkETajDHAW9RCl+lcTtzOEpPl3l8otHZa0xAjqfCQbyVYr5TXA7El6x8Kq ++Iz83GbpoYWOkjvXCvSoCZnuI2wzpTu2+nRmFXuNpPtyXy0Ia2JnSA1qA6DsZfvREQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794540248; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=khiKOGsNMTHDyzx2AtXgc6i62TVk9BvHYX6YqKL10pU=; b=bVRPfuImYB7tG1XJPsnRk1gXZtkWnGAN9fPhF+gI+KyZfbcDP08EtpGjMgbHH/0hT5tr uNKf+mbeD43H+8MZJIDYJwVmFrnbQSnRXggbUVX2bl8eUhCluyA7vVSTDprIl+9pUEjVy 7UBDWskS8OITQwftnwXweMiaOTgiOErTxg4HbH5KlQm2GelDkecxqYIK4qqq4CWYDqR06 MnffZHc/yy71PkCw0hyqbww7+qI1Dc5xbApaHwrTIMWpVVxigJFj17reh4u/GtOjvz5Ee 5WSg1rm+0kwf2kCI4ebmzHSoj0hjD3U5FQpMV8ty7I0HlUEduARvg7ghUBQuH5zjqCQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=m6u3TMxb; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7A3F0606A31C for ; Fri, 13 Nov 2026 03:24:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=m6u3TMxb Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9476F1F000C5; Fri, 13 Nov 2026 03:24:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794540248; bh=khiKOGsNMTHDyzx2AtXgc6i62TVk9BvHYX6YqKL10pU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=m6u3TMxb8t0xKt+ibA/VhjzrR6P0gfH6yjR5J7EK6nfrNeZRc7A79HCVlgLDFDJ2J BkDajVJGhOlJ0LGkAq6d7nlxIrPnalIKrqpQGib2JoGCnmhSyfFmV6AuwhJWce7iA6 tmgo/Ke8H405d+nBNcfDr//mXFpcfULSSJmNlsq96i040Ugd/GEUH9BQa6sRNkY0dr kGwPMgAcgeLl0i6K0mkrWH1h2P2aKYFhfN6gHVY3aF2y8z/nONWQrQx6FB+6cqLsF6 Kf2hVKjcioQ0hLVu03dUp4+DEqe0vW3dRY9QT61yJ3x4HdPSiAllyT5rCWfzykwfKx lXxxsih9DIK3A== From: Sasha Levin To: stable@vger.kernel.org Cc: Takashi Iwai , Bo Cao , Sasha Levin Subject: [PATCH 5.10.y] ALSA: pcm: Prevent O_APPEND open on OSS streams Date: Thu, 12 Nov 2026 22:24:06 -0500 Message-ID: <20261113032342.850566-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261109202903-failed-5.10-9017bc3d13da@kernel.org> References: <20261109202903-failed-5.10-9017bc3d13da@kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Takashi Iwai [ Upstream commit 9017bc3d13da0ea4e63be618c87143a7b69185e6 ] ALSA PCM core accepts to re-use the existing stream when O_APPEND is passed, and it's been used for dmix, etc. However, this mode isn't supposed to be used for OSS: the OSS stream allows re-configuration via its hw_params/hw_refine procedure even while it's being mmapped, so it implies the usage of only a single stream. Because of this assumption, the sanity check is skipped for OSS streams, and if user may attach to an existing OSS stream with O_APPEND, it may result in a UAF of the mapped pages which could be used as a privilege escalation exploit. For addressing it, this patch simply prohibits the O_APPEND behavior on the OSS stream. O_APPEND is never used for OSS layer itself, so this can't break for the right applications. Fixes: 0df63e44c3e3 ("[ALSA] Add O_APPEND flag support to PCM") Cc: stable@vger.kernel.org Reported-by: Bo Cao Link: https://lore.kernel.org/tencent_E90BB4F086165FAA3313723567A5C675EA06@qq.com Link: https://patch.msgid.link/20261103155844.120838-1-tiwai@suse.de Signed-off-by: Takashi Iwai [ sashal: Adjusted context for relocating the is_oss_stream macro because surrounding helpers are absent. ] Signed-off-by: Sasha Levin --- sound/core/pcm.c | 2 ++ sound/core/pcm_local.h | 6 ++++++ sound/core/pcm_native.c | 6 ------ 3 files changed, 8 insertions(+), 6 deletions(-) diff --git a/sound/core/pcm.c b/sound/core/pcm.c index bec81f6ba6ba5..d4eb842784143 100644 --- a/sound/core/pcm.c +++ b/sound/core/pcm.c @@ -930,6 +930,8 @@ int snd_pcm_attach_substream(struct snd_pcm *pcm, int stream, return -ENODEV; if (! SUBSTREAM_BUSY(substream)) return -EBADFD; + if (is_oss_stream(substream)) + return -EINVAL; substream->ref_count++; *rsubstream = substream; return 0; diff --git a/sound/core/pcm_local.h b/sound/core/pcm_local.h index b3e8be5aeafb3..353f675724337 100644 --- a/sound/core/pcm_local.h +++ b/sound/core/pcm_local.h @@ -72,4 +72,10 @@ struct page *snd_pcm_sgbuf_ops_page(struct snd_pcm_substream *substream, #define PCM_RUNTIME_CHECK(sub) snd_BUG_ON(!(sub) || !(sub)->runtime) +#if IS_ENABLED(CONFIG_SND_PCM_OSS) +#define is_oss_stream(substream) ((substream)->oss.oss) +#else +#define is_oss_stream(substream) false +#endif + #endif /* __SOUND_CORE_PCM_LOCAL_H */ diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c index 40020c5dceda0..7b6902bf0fd12 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -702,12 +702,6 @@ int snd_pcm_runtime_buffer_set_silence(struct snd_pcm_runtime *runtime) } EXPORT_SYMBOL_GPL(snd_pcm_runtime_buffer_set_silence); -#if IS_ENABLED(CONFIG_SND_PCM_OSS) -#define is_oss_stream(substream) ((substream)->oss.oss) -#else -#define is_oss_stream(substream) false -#endif - static int snd_pcm_hw_params(struct snd_pcm_substream *substream, struct snd_pcm_hw_params *params) { -- 2.53.0