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=1794532576; b=q8fZLZ+MWTFWcGFCfcI1Hyidh8J1MeDpgzlEYpebVVPcv4zDzalERnCwFatcrXN2LXmA ZTcQzzfAdRMRpSYU+TfjbUF72SHSrCXMH02V7xuvIK1VHPUqIGZ901RjzobDQaek2LyyK BxgXUUs7v04sjpo5VEwcp+97pMVykMBbGy2L2dCVZsu7BzyHIARG5Xa2Z7mLI/W9sQfHk CICZDgy4uXm3e41+yw92Q4rM8pouCO60I6xs+QW853X+SJb+lhrJw9VLWqkoaIouqPPtk sqGEocO7bweiP8BGA4/7C2CDvYzPrQ6Wt7Sy0XtvDsPsjgI1YOluwBZWErUqlqsEoDA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794532576; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=sgAwX9+IhmpneZ5BSBMTXN49tVh9L9lifbJ4zuEPejI=; b=qgSepLbWxXr+gCXsb10Tknv/nKjRC16EUkY4EUfRAXP33KVT7GkVULLmo0XVyLGUA6rT w/n49NOBtDIdngJof75e6aWNKzMaBGr8/Z0zGpfmh6K4VH0LnYlx03vOAga/2Eba5vSKP 3bzwP3F5kMHMDzRjPEaH3kYeE+nGw+rHRBbEhuLZXGM8oSu0IYxq8hWaaOpDFcYAexOKM x/3X3VhmwvRlHUMi18F83IK+qg+eVO6ZkX0Lsf+et+XEHIExcixXTTjZTDX92za0mhYMW wzZ7glldyMzhUQXr8o5niSYulYXxebKBFVsSgHNhLiQ6xQ+CqY+RcX6EoEF6kMgvbsA== 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=GEG8pXCg; 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 83F2B606A88D for ; Fri, 13 Nov 2026 01:16:16 +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=GEG8pXCg Received: by smtp.kernel.org (Postfix) with ESMTPSA id DA9AA1F000C6; Fri, 13 Nov 2026 01:16:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794532576; bh=sgAwX9+IhmpneZ5BSBMTXN49tVh9L9lifbJ4zuEPejI=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=GEG8pXCgGNUS3RpoHmkJhL7VimPr7RzQK8AqsdJqQb2cShy4GYKpChGcrl5ALyuu4 Ik1fMevei9nGwGYysdFBoTNCp3dXtVnOMCuMcYsXsNCfTgiU/0AGzuKEJ/eojH0joQ KDgfSrDduFx/E7gMGlTkDJvHd5VZhEl+++US8ttqmUqooa7yPdPl8oI1BuPN9TPbkZ +NTEPPHi4mp51Yg19WftggrJ3QwCuGnux+mtEMMIT2YDACIt/7ZYJRQfuuMs8Cgwuo WsKyOlpOy6TId1BwvN8shHeM3SyCHkDTTVTtnGU/c7gm6h1TgHfy0JQQyjU05y391l WT92rz4dFR/Dg== From: Sasha Levin To: stable@vger.kernel.org Cc: Takashi Iwai , Bo Cao , Sasha Levin Subject: [PATCH 6.6.y 2/2] ALSA: pcm: Prevent O_APPEND open on OSS streams Date: Thu, 12 Nov 2026 20:16:13 -0500 Message-ID: <20261113011600.592705-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261113011600.592705-1-sashal@kernel.org> References: <20261109201441-failed-6.6-9017bc3d13da@kernel.org> <20261113011600.592705-1-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 6d0c9c37796c2..af5bfb86656fd 100644 --- a/sound/core/pcm.c +++ b/sound/core/pcm.c @@ -933,6 +933,8 @@ 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 989e822c1059c..42570787e815d 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