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=1794532845; b=LnTydAKfp1m6mPH4QWGX0pXWpXloa+Pbpdi7hp9DxUkN+nLU+pOgcBHdPZ9L2XErLK9d xtCJ00b34tnBNKlaEZZKB1N/Dd/lhnNwkxc/onuhmNwcMjBp3LFKIPPseXWO2GhEMPjIB BoBSg+Q4JgPxuG7Ub1m+hId/Fggi1JWqZMk+JgRzo3wcQNQuQu8aeDGEoh/gC2HsYyC00 BQVTohl61hNcidVpRlJuz9M/TU72f/RY6XbXG1rJ7N1c980vr9QCY76toQRqZ44KnvhYS Dy/39+snUbsKpp4dqR2ZomEayFeR39pEx9sTAW1RcFcBVU3kGXWnGjJvihLAVLoXyAw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794532845; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=eNsRFqYJH5ye39ruMwzLDQ4ZIBWc7fDtPr4uqABETjE=; b=4VbWb70c9WIkoPFV736tHJPS4erTG8rFSzBcn+0J+Q4KYnMk/tQAnon1vR/2qWtCpRrW I7vyc+6LscOPYMB9QVt3FZ5Ut0p1jFZi8qbFux2fLGW6wcNh29cS4Kup4a2ZzWSj60Q+q Ta7k2WyYcSMEoyfw1WD7eLFDLBqh0dc7kUqMb2Byxyo5DgT5H5dBNhCaRWzPCuhtdc+yD Ftqyx5ILi0k+tc8dRiKFXRdVf7Qi8TIGf9pusob5XakXUDfKjZr4IYIWk7wUsnF6KNJxF 3Umu6cfYHgb/gnVX+IVfFkL65nkaGLbbCkq/+i1Yn0RjCe5f/YhbfDV1Ft2ecoDmdsw== 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="kc/Rihof"; 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 5C6DB606A32E for ; Fri, 13 Nov 2026 01:20:45 +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=kc/Rihof Received: by smtp.kernel.org (Postfix) with ESMTPSA id B79861F000C6; Fri, 13 Nov 2026 01:20:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794532845; bh=eNsRFqYJH5ye39ruMwzLDQ4ZIBWc7fDtPr4uqABETjE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=kc/RihofNdjTdO53MT/gvdKPU+LNDLal4hY4XqXBJNl/nCqftSw7QZUzH1AAhCP7W fawPNEPKiUBRxKSadk/wYDzE0c1U4zEKPooxgWu9czRjxbfOwdEVMbyuXechuWOyf0 QNuhhDdsCE5MYNKwN8qxBisO8py7fniB0eOqAcyKDh0x6Pl053i32gsYWFfO0nQSG5 AxURgHZJIPJRtZ6HU6ngpRGSKN/FMmDXZMv7kYsNIy/KA6naZ3COECWn9IiWRmSm/d U8OMQtNaYCzIVE+L5YAWwXBJV2L8059SM/+nRCHoaOWnbQPvVBymPr+hkbsfAsh1Jj QhH42vcI2DugA== From: Sasha Levin To: stable@vger.kernel.org Cc: Takashi Iwai , Bo Cao , Sasha Levin Subject: [PATCH 6.1.y 2/2] ALSA: pcm: Prevent O_APPEND open on OSS streams Date: Thu, 12 Nov 2026 20:20:42 -0500 Message-ID: <20261113012028.613052-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261113012028.613052-1-sashal@kernel.org> References: <20261109201939-failed-6.1-9017bc3d13da@kernel.org> <20261113012028.613052-1-sashal@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 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 2415a3c3ac6c9..a8d10a844e51e 100644 --- a/sound/core/pcm.c +++ b/sound/core/pcm.c @@ -932,6 +932,8 @@ 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 ecb21697ae3a4..4b134d435c24f 100644 --- a/sound/core/pcm_local.h +++ b/sound/core/pcm_local.h @@ -80,4 +80,10 @@ static inline void snd_pcm_dma_buffer_sync(struct snd_pcm_substream *substream, snd_dma_buffer_sync(snd_pcm_get_dma_buf(substream), mode); } +#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 e015f34ce463c..9e87aa2518411 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -720,12 +720,6 @@ 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 void pcm_qos_req_clear(struct snd_pcm_substream *substream) { if (cpu_latency_qos_request_active(&substream->latency_pm_qos_req)) -- 2.53.0