Patch "ALSA: rawmidi: Avoid racy info ioctl via ctl device" has been added to the 4.4-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ALSA: rawmidi: Avoid racy info ioctl via ctl device

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     alsa-rawmidi-avoid-racy-info-ioctl-via-ctl-device.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From c1cfd9025cc394fd137a01159d74335c5ac978ce Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@xxxxxxx>
Date: Thu, 14 Dec 2017 16:44:12 +0100
Subject: ALSA: rawmidi: Avoid racy info ioctl via ctl device

From: Takashi Iwai <tiwai@xxxxxxx>

commit c1cfd9025cc394fd137a01159d74335c5ac978ce upstream.

The rawmidi also allows to obtaining the information via ioctl of ctl
API.  It means that user can issue an ioctl to the rawmidi device even
when it's being removed as long as the control device is present.
Although the code has some protection via the global register_mutex,
its range is limited to the search of the corresponding rawmidi
object, and the mutex is already unlocked at accessing the rawmidi
object.  This may lead to a use-after-free.

For avoiding it, this patch widens the application of register_mutex
to the whole snd_rawmidi_info_select() function.  We have another
mutex per rawmidi object, but this operation isn't very hot path, so
it shouldn't matter from the performance POV.

Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 sound/core/rawmidi.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

--- a/sound/core/rawmidi.c
+++ b/sound/core/rawmidi.c
@@ -579,15 +579,14 @@ static int snd_rawmidi_info_user(struct
 	return 0;
 }
 
-int snd_rawmidi_info_select(struct snd_card *card, struct snd_rawmidi_info *info)
+static int __snd_rawmidi_info_select(struct snd_card *card,
+				     struct snd_rawmidi_info *info)
 {
 	struct snd_rawmidi *rmidi;
 	struct snd_rawmidi_str *pstr;
 	struct snd_rawmidi_substream *substream;
 
-	mutex_lock(&register_mutex);
 	rmidi = snd_rawmidi_search(card, info->device);
-	mutex_unlock(&register_mutex);
 	if (!rmidi)
 		return -ENXIO;
 	if (info->stream < 0 || info->stream > 1)
@@ -603,6 +602,16 @@ int snd_rawmidi_info_select(struct snd_c
 	}
 	return -ENXIO;
 }
+
+int snd_rawmidi_info_select(struct snd_card *card, struct snd_rawmidi_info *info)
+{
+	int ret;
+
+	mutex_lock(&register_mutex);
+	ret = __snd_rawmidi_info_select(card, info);
+	mutex_unlock(&register_mutex);
+	return ret;
+}
 EXPORT_SYMBOL(snd_rawmidi_info_select);
 
 static int snd_rawmidi_info_select_user(struct snd_card *card,


Patches currently in stable-queue which might be from tiwai@xxxxxxx are

queue-4.4/alsa-usb-audio-fix-the-missing-ctl-name-suffix-at-parsing-su.patch
queue-4.4/alsa-rawmidi-avoid-racy-info-ioctl-via-ctl-device.patch
queue-4.4/acpi-apei-erst-fix-missing-error-handling-in-erst_reader.patch