[PATCH 3.16 213/366] ALSA: seq: oss: Hardening for potential Spectre v1

Ben Hutchings
2018-10-14T15:25:41Z

From: Takashi Iwai <tiwai@suse.de>

commit 8d218dd8116695ecda7164f97631c069938aa22e upstream.

As Smatch recently suggested, a few places in OSS sequencer codes may
expand the array directly from the user-space value with speculation,
namely there are a significant amount of references to either
info->ch[] or dp->synths[] array:

sound/core/seq/oss/seq_oss_event.c:315 note_on_event() warn: potential spectre issue 'info->ch' (local cap)
sound/core/seq/oss/seq_oss_event.c:362 note_off_event() warn: potential spectre issue 'info->ch' (local cap)
sound/core/seq/oss/seq_oss_synth.c:470 snd_seq_oss_synth_load_patch() warn: potential spectre issue 'dp->synths' (local cap)
sound/core/seq/oss/seq_oss_event.c:293 note_on_event() warn: potential spectre issue 'dp->synths'
sound/core/seq/oss/seq_oss_event.c:353 note_off_event() warn: potential spectre issue 'dp->synths'
sound/core/seq/oss/seq_oss_synth.c:506 snd_seq_oss_synth_sysex() warn: potential spectre issue 'dp->synths'
sound/core/seq/oss/seq_oss_synth.c:580 snd_seq_oss_synth_ioctl() warn: potential spectre issue 'dp->synths'

Although all these seem doing only the first load without further
reference, we may want to stay in a safer side, so hardening with
array_index_nospec() would still make sense.

We may put array_index_nospec() at each place, but here we take a
different approach:

- For dp->synths[], change the helpers to retrieve seq_oss_synthinfo
pointer directly instead of the array expansion at each place

- For info->ch[], harden in a normal way, as there are only a couple
of places

As a result, the existing helper, snd_seq_oss_synth_is_valid() is
replaced with snd_seq_oss_synth_info(). Also, we cover MIDI device
where a similar array expansion is done, too, although it wasn't
reported by Smatch.

BugLink: https://marc.info/?l=linux-kernel&m=152411496503418&w=2
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
sound/core/seq/oss/seq_oss_event.c | 15 +++---
sound/core/seq/oss/seq_oss_midi.c | 2 +
sound/core/seq/oss/seq_oss_synth.c | 75 +++++++++++++++++-------------
sound/core/seq/oss/seq_oss_synth.h | 3 +-
4 files changed, 55 insertions(+), 40 deletions(-)

--- a/sound/core/seq/oss/seq_oss_event.c
+++ b/sound/core/seq/oss/seq_oss_event.c
@@ -26,6 +26,7 @@
#include <sound/seq_oss_legacy.h>
#include "seq_oss_readq.h"
#include "seq_oss_writeq.h"
+#include <linux/nospec.h>

/*
@@ -287,10 +288,10 @@ note_on_event(struct seq_oss_devinfo *dp
{
struct seq_oss_synthinfo *info;

- if (!snd_seq_oss_synth_is_valid(dp, dev))
+ info = snd_seq_oss_synth_info(dp, dev);
+ if (!info)
return -ENXIO;

- info = &dp->synths[dev];
switch (info->arg.event_passing) {
case SNDRV_SEQ_OSS_PROCESS_EVENTS:
if (! info->ch || ch < 0 || ch >= info->nr_voices) {
@@ -298,6 +299,7 @@ note_on_event(struct seq_oss_devinfo *dp
return set_note_event(dp, dev, SNDRV_SEQ_EVENT_NOTEON, ch, note, vel, ev);
}

+ ch = array_index_nospec(ch, info->nr_voices);
if (note == 255 && info->ch[ch].note >= 0) {
/* volume control */
int type;
@@ -347,10 +349,10 @@ note_off_event(struct seq_oss_devinfo *d
{
struct seq_oss_synthinfo *info;

- if (!snd_seq_oss_synth_is_valid(dp, dev))
+ info = snd_seq_oss_synth_info(dp, dev);
+ if (!info)
return -ENXIO;

- info = &dp->synths[dev];
switch (info->arg.event_passing) {
case SNDRV_SEQ_OSS_PROCESS_EVENTS:
if (! info->ch || ch < 0 || ch >= info->nr_voices) {
@@ -358,6 +360,7 @@ note_off_event(struct seq_oss_devinfo *d
return set_note_event(dp, dev, SNDRV_SEQ_EVENT_NOTEON, ch, note, vel, ev);
}

+ ch = array_index_nospec(ch, info->nr_voices);
if (info->ch[ch].note >= 0) {
note = info->ch[ch].note;
info->ch[ch].vel = 0;
@@ -381,7 +384,7 @@ note_off_event(struct seq_oss_devinfo *d
static int
set_note_event(struct seq_oss_devinfo *dp, int dev, int type, int ch, int note, int vel, struct snd_seq_event *ev)
{
- if (! snd_seq_oss_synth_is_valid(dp, dev))
+ if (!snd_seq_oss_synth_info(dp, dev))
return -ENXIO;

ev->type = type;
@@ -399,7 +402,7 @@ set_note_event(struct seq_oss_devinfo *d
static int
set_control_event(struct seq_oss_devinfo *dp, int dev, int type, int ch, int param, int val, struct snd_seq_event *ev)
{
- if (! snd_seq_oss_synth_is_valid(dp, dev))
+ if (!snd_seq_oss_synth_info(dp, dev))
return -ENXIO;

ev->type = type;
--- a/sound/core/seq/oss/seq_oss_midi.c
+++ b/sound/core/seq/oss/seq_oss_midi.c
@@ -29,6 +29,7 @@
#include "../seq_lock.h"
#include <linux/init.h>
#include <linux/slab.h>
+#include <linux/nospec.h>

/*
@@ -318,6 +319,7 @@ get_mididev(struct seq_oss_devinfo *dp,
{
if (dev < 0 || dev >= dp->max_mididev)
return NULL;
+ dev = array_index_nospec(dev, dp->max_mididev);
return get_mdev(dev);
}

--- a/sound/core/seq/oss/seq_oss_synth.c
+++ b/sound/core/seq/oss/seq_oss_synth.c
@@ -26,6 +26,7 @@
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
+#include <linux/nospec.h>

/*
* constants
@@ -339,17 +340,13 @@ snd_seq_oss_synth_cleanup(struct seq_oss
dp->max_synthdev = 0;
}

-/*
- * check if the specified device is MIDI mapped device
- */
-static int
-is_midi_dev(struct seq_oss_devinfo *dp, int dev)
+static struct seq_oss_synthinfo *
+get_synthinfo_nospec(struct seq_oss_devinfo *dp, int dev)
{
if (dev < 0 || dev >= dp->max_synthdev)
- return 0;
- if (dp->synths[dev].is_midi)
- return 1;
- return 0;
+ return NULL;
+ dev = array_index_nospec(dev, SNDRV_SEQ_OSS_MAX_SYNTH_DEVS);
+ return &dp->synths[dev];
}

/*
@@ -359,11 +356,13 @@ static struct seq_oss_synth *
get_synthdev(struct seq_oss_devinfo *dp, int dev)
{
struct seq_oss_synth *rec;
- if (dev < 0 || dev >= dp->max_synthdev)
+ struct seq_oss_synthinfo *info = get_synthinfo_nospec(dp, dev);
+
+ if (!info)
return NULL;
- if (! dp->synths[dev].opened)
+ if (!info->opened)
return NULL;
- if (dp->synths[dev].is_midi) {
+ if (info->is_midi) {
rec = &midi_synth_dev;
snd_use_lock_use(&rec->use_lock);
} else {
@@ -406,10 +405,8 @@ snd_seq_oss_synth_reset(struct seq_oss_d
struct seq_oss_synth *rec;
struct seq_oss_synthinfo *info;

- if (snd_BUG_ON(dev < 0 || dev >= dp->max_synthdev))
- return;
- info = &dp->synths[dev];
- if (! info->opened)
+ info = get_synthinfo_nospec(dp, dev);
+ if (!info || !info->opened)
return;
if (info->sysex)
info->sysex->len = 0; /* reset sysex */
@@ -458,12 +455,14 @@ snd_seq_oss_synth_load_patch(struct seq_
const char __user *buf, int p, int c)
{
struct seq_oss_synth *rec;
+ struct seq_oss_synthinfo *info;
int rc;

- if (dev < 0 || dev >= dp->max_synthdev)
+ info = get_synthinfo_nospec(dp, dev);
+ if (!info)
return -ENXIO;

- if (is_midi_dev(dp, dev))
+ if (info->is_midi)
return 0;
if ((rec = get_synthdev(dp, dev)) == NULL)
return -ENXIO;
@@ -471,24 +470,25 @@ snd_seq_oss_synth_load_patch(struct seq_
if (rec->oper.load_patch == NULL)
rc = -ENXIO;
else
- rc = rec->oper.load_patch(&dp->synths[dev].arg, fmt, buf, p, c);
+ rc = rec->oper.load_patch(&info->arg, fmt, buf, p, c);
snd_use_lock_free(&rec->use_lock);
return rc;
}

/*
- * check if the device is valid synth device
+ * check if the device is valid synth device and return the synth info
*/
-int
-snd_seq_oss_synth_is_valid(struct seq_oss_devinfo *dp, int dev)
+struct seq_oss_synthinfo *
+snd_seq_oss_synth_info(struct seq_oss_devinfo *dp, int dev)
{
struct seq_oss_synth *rec;
+
rec = get_synthdev(dp, dev);
if (rec) {
snd_use_lock_free(&rec->use_lock);
- return 1;
+ return get_synthinfo_nospec(dp, dev);
}
- return 0;
+ return NULL;
}

@@ -503,16 +503,18 @@ snd_seq_oss_synth_sysex(struct seq_oss_d
int i, send;
unsigned char *dest;
struct seq_oss_synth_sysex *sysex;
+ struct seq_oss_synthinfo *info;

- if (! snd_seq_oss_synth_is_valid(dp, dev))
+ info = snd_seq_oss_synth_info(dp, dev);
+ if (!info)
return -ENXIO;

- sysex = dp->synths[dev].sysex;
+ sysex = info->sysex;
if (sysex == NULL) {
sysex = kzalloc(sizeof(*sysex), GFP_KERNEL);
if (sysex == NULL)
return -ENOMEM;
- dp->synths[dev].sysex = sysex;
+ info->sysex = sysex;
}

send = 0;
@@ -557,10 +559,12 @@ snd_seq_oss_synth_sysex(struct seq_oss_d
int
snd_seq_oss_synth_addr(struct seq_oss_devinfo *dp, int dev, struct snd_seq_event *ev)
{
- if (! snd_seq_oss_synth_is_valid(dp, dev))
+ struct seq_oss_synthinfo *info = snd_seq_oss_synth_info(dp, dev);
+
+ if (!info)
return -EINVAL;
- snd_seq_oss_fill_addr(dp, ev, dp->synths[dev].arg.addr.client,
- dp->synths[dev].arg.addr.port);
+ snd_seq_oss_fill_addr(dp, ev, info->arg.addr.client,
+ info->arg.addr.port);
return 0;
}

@@ -572,16 +576,18 @@ int
snd_seq_oss_synth_ioctl(struct seq_oss_devinfo *dp, int dev, unsigned int cmd, unsigned long addr)
{
struct seq_oss_synth *rec;
+ struct seq_oss_synthinfo *info;
int rc;

- if (is_midi_dev(dp, dev))
+ info = get_synthinfo_nospec(dp, dev);
+ if (!info || info->is_midi)
return -ENXIO;
if ((rec = get_synthdev(dp, dev)) == NULL)
return -ENXIO;
if (rec->oper.ioctl == NULL)
rc = -ENXIO;
else
- rc = rec->oper.ioctl(&dp->synths[dev].arg, cmd, addr);
+ rc = rec->oper.ioctl(&info->arg, cmd, addr);
snd_use_lock_free(&rec->use_lock);
return rc;
}
@@ -593,7 +599,10 @@ snd_seq_oss_synth_ioctl(struct seq_oss_d
int
snd_seq_oss_synth_raw_event(struct seq_oss_devinfo *dp, int dev, unsigned char *data, struct snd_seq_event *ev)
{
- if (! snd_seq_oss_synth_is_valid(dp, dev) || is_midi_dev(dp, dev))
+ struct seq_oss_synthinfo *info;
+
+ info = snd_seq_oss_synth_info(dp, dev);
+ if (!info || info->is_midi)
return -ENXIO;
ev->type = SNDRV_SEQ_EVENT_OSS;
memcpy(ev->data.raw8.d, data, 8);
--- a/sound/core/seq/oss/seq_oss_synth.h
+++ b/sound/core/seq/oss/seq_oss_synth.h
@@ -37,7 +37,8 @@ void snd_seq_oss_synth_cleanup(struct se
void snd_seq_oss_synth_reset(struct seq_oss_devinfo *dp, int dev);
int snd_seq_oss_synth_load_patch(struct seq_oss_devinfo *dp, int dev, int fmt,
const char __user *buf, int p, int c);
-int snd_seq_oss_synth_is_valid(struct seq_oss_devinfo *dp, int dev);
+struct seq_oss_synthinfo *snd_seq_oss_synth_info(struct seq_oss_devinfo *dp,
+ int dev);
int snd_seq_oss_synth_sysex(struct seq_oss_devinfo *dp, int dev, unsigned char *buf,
struct snd_seq_event *ev);
int snd_seq_oss_synth_addr(struct seq_oss_devinfo *dp, int dev, struct snd_seq_event *ev);