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=1794532267; b=LHcweJ9dkcuijdRSxT1AudcvmFAcj9P/DwFVGwZ8j0TwuA+kz+eXbjvSQtiWy7m4Qt0P +MklnllGclY/aS88weZvMBipSshvrsBoG4BRpHAl7VZjhZ/X4WcTeknArGGUZ6R4vt42d 0+DsmpmL6sbGoj6AGPkMVWqPbivkrUztMZ1/uulIf4ORi40ogEzBGEUOknXuyXgvc6n2h BcGJAdZfeZHkh5GJLMTrJwHcjnp2bKr93B345DOuKiUUgkgx/pU0OrjipCXESv5fYIZD0 40xUZe7o8zNASiKNiY5nsBoFR5DWDsl2cRzb3e0qC4CKwv1QJ4dfDhDpKKFnZQn4+EA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794532267; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=8Gn0m0E/X22IuLoSl4exbuKUJmUWUuLBd4XdNpIBu+Y=; b=abBaf5VHPGfhQBg+L1NLiRgZGhPjpB/WvOmEiMTUyyIilQOLYio5KwaFNYWpXr0983AL dV9tu8Z2NKYsUw6dlCXrWtSFiS3glM03sxyO2HlPba/6JqyLfA1cTHb1b6mn6PE+owlU7 s3hvqbSgkhwsPVESZvssXNprXhgOxVnK0DK55fwmZMY6Gk8D4W2Qa8jlWEiwwzRA8xqGs SVeRPW1ekaBpVVwBDD2LXHRUYFBxbm7LH9gHn52gGOrl45iYvmgaVtDuzmX8nkLQ73F3A t3eIKDKq+FPCttGe8ikk1AGe24LWrxYMvAu06BghuejKkk6R7czb1n1Wvk15pozvILw== 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=Fy07+AOA; 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 B1850606A323 for ; Fri, 13 Nov 2026 01:11:07 +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=Fy07+AOA Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1C24B1F000C5; Fri, 13 Nov 2026 01:11:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794532267; bh=8Gn0m0E/X22IuLoSl4exbuKUJmUWUuLBd4XdNpIBu+Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Fy07+AOAm0+LDlpFxgIvTGcIa2584vW1EAMypDN+MgPR0E2Vf0QdMYXNPoT6w1fuw Jyns2cL5TdkFoukpwXAsHgWs5eIasEtZetj19vuWkwakxZgM116SgRXodroeilxkkM Icq17Lifh+5P9pNmpS99B5VIlKXtdTPzoNfTx1XdEfn5c/CHggqpJnGqNFA1LAzMsG C63tQ/zf/mQjY1GR4i+tPoxwCZfJkMS3HZuflrMNDJoFZ1cjqM1MvvEBOVEoT901DP rWBTwELaH2nOBTWdxezy4Rta+0pqmzYdib4H/ADEp/Kvou3zGX/XYU/oswb9jnyfxc cAAYXZ3iHvEHg== From: Sasha Levin To: stable@vger.kernel.org Cc: Takashi Iwai , Bo Cao , Sasha Levin Subject: [PATCH 6.12.y 2/2] ALSA: pcm: Prevent O_APPEND open on OSS streams Date: Thu, 12 Nov 2026 20:11:05 -0500 Message-ID: <20261113011054.553203-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261113011054.553203-1-sashal@kernel.org> References: <20261109201011-failed-6.12-9017bc3d13da@kernel.org> <20261113011054.553203-1-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 ff1e9f8c1ecae..18979f88f7159 100644 --- a/sound/core/pcm.c +++ b/sound/core/pcm.c @@ -923,6 +923,8 @@ 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 f3b17ec2f1778..24b923aabc9a2 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -745,12 +745,6 @@ 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