FAILED: patch "[PATCH] ALSA: pcm: Prevent O_APPEND open on OSS streams" failed to apply to 6.6-stable tree

PATCH New Sasha Levin 1 participant 3 messages Nov 10 – Nov 13

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Sasha Levin

author maintainer

2026-11-10 01:14 UTC #0 lore raw

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 9017bc3d13da0ea4e63be618c87143a7b69185e6
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '[email protected]' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 9017bc3d13da0ea4e63be618c87143a7b69185e6 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <[email protected]>
Date: Tue, 3 Nov 2026 16:58:40 +0100
Subject: [PATCH] ALSA: pcm: Prevent O_APPEND open on OSS streams

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 [email protected]

Reported-by Bo Cao <[email protected]>

Link https://lore.kernel.org/[email protected] open here

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Takashi Iwai <[email protected]>

---
 sound/core/pcm.c        | 2 ++
 sound/core/pcm_local.h  | 6 ++++++
 sound/core/pcm_native.c | 6 ------
 3 files changed, 8 insertions(+), 6 deletions(-)

sound/core/pcm.c +2 -0

index 064df4cd3b50e..6c8274414c226 100644
@@ -929,6 +929,8 @@ 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;

sound/core/pcm_local.h +6 -0

index ecb21697ae3a4..4b134d435c24f 100644
@@ -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 */

sound/core/pcm_native.c +0 -6

index 35152fae74ca2..bec797398acf7 100644
@@ -749,12 +749,6 @@ 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))

Signature · 1 line

2.53.0

Sasha Levin

author maintainer

2026-11-13 01:16 UTC #1 lore raw

PATCH 1/2 ALSA: pcm: Optimize cpu_latency_qos_*() calls

From: Takashi Iwai <[email protected]>

[ Upstream commit 9f6f4e97fd53908aecb0979507d9ff10a22288eb ]

We have a few cpu_latency_qos_*() calls in PCM callbacks, but they seem suboptimal in a few aspects:
- We call them at each time when the hw_params changed, but explicitly do remove and (re-)add; this could be cpu_latency_qos_update_request(), instead
- The setup of cpu_latency_qos_*() doesn't have to be in hw_params at all; it's not the place where the actual parameters are set up, but rather better at the prepare callback.
- The hw_free calls cpu_latency_qos_remove_request() unconditionally, which may be poking a WARNING when it wasn't queued.

For addressing the issues above, this patch cleans up and reorganize the cpu_latency_qos_*() calls in the PCM core by a couple helper functions. Now, they are set up at prepare callback, and cleared at hw_free and release callbacks via the new helpers.

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Takashi Iwai <[email protected]>

Stable-dep-of: 9017bc3d13da ("ALSA: pcm: Prevent O_APPEND open on OSS streams")

Signed-off-by Sasha Levin <[email protected]>

---
 sound/core/pcm_native.c | 35 +++++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)

sound/core/pcm_native.c +25 ~~-10~~

index 4b570d8aa80eb..989e822c1059c 100644
@@ -726,11 +726,32 @@ EXPORT_SYMBOL_GPL(snd_pcm_runtime_buffer_set_silence);
 #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))
+		cpu_latency_qos_remove_request(&substream->latency_pm_qos_req);
+}
+
+static void pcm_qos_req_update(struct snd_pcm_substream *substream, int usecs)
+{
+	if (usecs < 0) {
+		pcm_qos_req_clear(substream);
+		return;
+	}
+
+	if (cpu_latency_qos_request_active(&substream->latency_pm_qos_req))
+		cpu_latency_qos_update_request(&substream->latency_pm_qos_req,
+					       usecs);
+	else
+		cpu_latency_qos_add_request(&substream->latency_pm_qos_req,
+					    usecs);
+}
+
 static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
 			     struct snd_pcm_hw_params *params)
 {
 	struct snd_pcm_runtime *runtime;
-	int err, usecs;
+	int err;
 	unsigned int bits;
 	snd_pcm_uframes_t frames;

@@ -837,12 +858,6 @@ static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
 	snd_pcm_timer_resolution_change(substream);
 	snd_pcm_set_state(substream, SNDRV_PCM_STATE_SETUP);
 
-	if (cpu_latency_qos_request_active(&substream->latency_pm_qos_req))
-		cpu_latency_qos_remove_request(&substream->latency_pm_qos_req);
-	usecs = period_to_usecs(runtime);
-	if (usecs >= 0)
-		cpu_latency_qos_add_request(&substream->latency_pm_qos_req,
-					    usecs);
 	err = 0;
  _error:
 	if (err) {

@@ -921,7 +936,7 @@ static int snd_pcm_hw_free(struct snd_pcm_substream *substream)
 		goto unlock;
 	result = do_hw_free(substream);
 	snd_pcm_set_state(substream, SNDRV_PCM_STATE_OPEN);
-	cpu_latency_qos_remove_request(&substream->latency_pm_qos_req);
+	pcm_qos_req_clear(substream);
  unlock:
 	snd_pcm_buffer_access_unlock(runtime);
 	return result;

@@ -1976,6 +1991,7 @@ static int snd_pcm_do_prepare(struct snd_pcm_substream *substream,
 	err = substream->ops->prepare(substream);
 	if (err < 0)
 		return err;
+	pcm_qos_req_update(substream, period_to_usecs(substream->runtime));
 	return snd_pcm_do_reset(substream, state);
 }

@@ -2750,8 +2766,7 @@ void snd_pcm_release_substream(struct snd_pcm_substream *substream)
 		substream->ops->close(substream);
 		substream->hw_opened = 0;
 	}
-	if (cpu_latency_qos_request_active(&substream->latency_pm_qos_req))
-		cpu_latency_qos_remove_request(&substream->latency_pm_qos_req);
+	pcm_qos_req_clear(substream);
 	if (substream->pcm_release) {
 		substream->pcm_release(substream);
 		substream->pcm_release = NULL;

Signature · 1 line

2.53.0

Sasha Levin

author maintainer

2026-11-13 01:16 UTC #2 lore raw

PATCH 2/2 ALSA: pcm: Prevent O_APPEND open on OSS streams

From: Takashi Iwai <[email protected]>

[ Upstream commit 9017bc3d13da0ea4e63be618c87143a7b69185e6 ]

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 [email protected]

Reported-by Bo Cao <[email protected]>

Link https://lore.kernel.org/[email protected] open here

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Takashi Iwai <[email protected]>

Signed-off-by Sasha Levin <[email protected]>

---
 sound/core/pcm.c        | 2 ++
 sound/core/pcm_local.h  | 6 ++++++
 sound/core/pcm_native.c | 6 ------
 3 files changed, 8 insertions(+), 6 deletions(-)

sound/core/pcm.c +2 -0

index 6d0c9c37796c2..af5bfb86656fd 100644
@@ -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;

sound/core/pcm_local.h +6 -0

index ecb21697ae3a4..4b134d435c24f 100644
@@ -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 */

sound/core/pcm_native.c +0 -6

index 989e822c1059c..42570787e815d 100644
@@ -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))

Signature · 1 line

2.53.0