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authorZhang Cen <rollkingzzc@gmail.com>2026-05-27 14:29:48 +0800
committerTakashi Iwai <tiwai@suse.de>2026-05-27 12:34:29 +0200
commitef7607ab1c8adc6258fb1b27d08e26aecdc18a58 (patch)
tree54a394ad3c373ecabfe24078ac06567c10c5aa76 /sound
parent06363f96e3d6b54ff7b5d2ce85cab95bd5e874b0 (diff)
downloadlinux-next-history-ef7607ab1c8adc6258fb1b27d08e26aecdc18a58.tar.gz
ALSA: seq: midi: Serialize output teardown with event_input
event_process_midi() borrows msynth->output_rfile.output and then passes the substream to dump_midi() and snd_rawmidi_kernel_write() without synchronizing with the output open/close transition. midisynth_use() also publishes output_rfile before snd_rawmidi_output_params() has finished. The last midisynth_unuse() can therefore release the same rawmidi file and free substream->runtime before snd_rawmidi_kernel_write1() takes its runtime buffer reference. That leaves the event_input path using a stale substream or runtime and can end in a NULL-deref or use-after-free. Fix this with two pieces of synchronization. Keep a short IRQ-safe spinlock only for publishing or clearing output_rfile and for pairing the output snapshot with an snd_use_lock_t reference. Once event_process_midi() has taken that in-flight reference, it drops the spinlock before calling snd_seq_dump_var_event(), dump_midi(), or snd_rawmidi_kernel_write(). midisynth_unuse() now detaches the visible rawmidi file under the same spinlock, waits for the in-flight writers to drain, and only then drains and releases the saved file. midisynth_use() likewise opens into a local snd_rawmidi_file and publishes it only after snd_rawmidi_output_params() succeeds. The buggy scenario involves two paths, with each column showing the order within that path: event_input path: last unuse path: 1. event_process_midi() snapshots 1. midisynth_unuse() starts output_rfile.output. tearing down output_rfile. 2. dump_midi() reaches 2. snd_rawmidi_kernel_release() snd_rawmidi_kernel_write() closes the output file. before runtime is pinned. 3. close_substream() frees 3. The callback keeps using substream->runtime. the borrowed substream. Validation reproduced this kernel report: KASAN null-ptr-deref in snd_rawmidi_kernel_write1+0x56/0x360 RIP: 0033:0x7fde7dd0837f RIP: 0010:snd_rawmidi_kernel_write1+0x56/0x360 Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Assisted-by: Codex:gpt-5.5 Signed-off-by: Zhang Cen <rollkingzzc@gmail.com> Link: https://patch.msgid.link/20260527062948.3614025-1-rollkingzzc@gmail.com Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound')
-rw-r--r--sound/core/seq/seq_midi.c55
1 files changed, 41 insertions, 14 deletions
diff --git a/sound/core/seq/seq_midi.c b/sound/core/seq/seq_midi.c
index ca3f5fc309927..2eb12199c92f9 100644
--- a/sound/core/seq/seq_midi.c
+++ b/sound/core/seq/seq_midi.c
@@ -24,6 +24,7 @@ Possible options for midisynth module:
#include <sound/seq_device.h>
#include <sound/seq_midi_event.h>
#include <sound/initval.h>
+#include "seq_lock.h"
MODULE_AUTHOR("Frank van de Pol <fvdpol@coil.demon.nl>, Jaroslav Kysela <perex@perex.cz>");
MODULE_DESCRIPTION("Advanced Linux Sound Architecture sequencer MIDI synth.");
@@ -42,6 +43,8 @@ struct seq_midisynth {
int device;
int subdevice;
struct snd_rawmidi_file input_rfile;
+ spinlock_t output_lock; /* protects output_rfile publication */
+ snd_use_lock_t output_use_lock; /* in-flight event_input users */
struct snd_rawmidi_file output_rfile;
int seq_client;
int seq_port;
@@ -125,31 +128,42 @@ static int event_process_midi(struct snd_seq_event *ev, int direct,
struct seq_midisynth *msynth = private_data;
unsigned char msg[10]; /* buffer for constructing midi messages */
struct snd_rawmidi_substream *substream;
+ int err = 0;
int len;
if (snd_BUG_ON(!msynth))
return -EINVAL;
- substream = msynth->output_rfile.output;
- if (substream == NULL)
- return -ENODEV;
+
+ scoped_guard(spinlock_irqsave, &msynth->output_lock) {
+ substream = msynth->output_rfile.output;
+ if (!substream)
+ return -ENODEV;
+ snd_use_lock_use(&msynth->output_use_lock);
+ }
+
if (ev->type == SNDRV_SEQ_EVENT_SYSEX) { /* special case, to save space */
if ((ev->flags & SNDRV_SEQ_EVENT_LENGTH_MASK) != SNDRV_SEQ_EVENT_LENGTH_VARIABLE) {
/* invalid event */
pr_debug("ALSA: seq_midi: invalid sysex event flags = 0x%x\n", ev->flags);
- return 0;
+ goto out;
}
snd_seq_dump_var_event(ev, __dump_midi, substream);
snd_midi_event_reset_decode(msynth->parser);
} else {
- if (msynth->parser == NULL)
- return -EIO;
+ if (!msynth->parser) {
+ err = -EIO;
+ goto out;
+ }
len = snd_midi_event_decode(msynth->parser, msg, sizeof(msg), ev);
if (len < 0)
- return 0;
+ goto out;
if (dump_midi(substream, msg, len) < 0)
snd_midi_event_reset_decode(msynth->parser);
}
- return 0;
+
+out:
+ snd_use_lock_free(&msynth->output_use_lock);
+ return err;
}
@@ -163,6 +177,8 @@ static int snd_seq_midisynth_new(struct seq_midisynth *msynth,
msynth->card = card;
msynth->device = device;
msynth->subdevice = subdevice;
+ spin_lock_init(&msynth->output_lock);
+ snd_use_lock_init(&msynth->output_use_lock);
return 0;
}
@@ -215,12 +231,13 @@ static int midisynth_use(void *private_data, struct snd_seq_port_subscribe *info
{
int err;
struct seq_midisynth *msynth = private_data;
+ struct snd_rawmidi_file rfile = {};
struct snd_rawmidi_params params;
/* open midi port */
err = snd_rawmidi_kernel_open(msynth->rmidi, msynth->subdevice,
SNDRV_RAWMIDI_LFLG_OUTPUT,
- &msynth->output_rfile);
+ &rfile);
if (err < 0) {
pr_debug("ALSA: seq_midi: midi output open failed!!!\n");
return err;
@@ -229,12 +246,14 @@ static int midisynth_use(void *private_data, struct snd_seq_port_subscribe *info
params.avail_min = 1;
params.buffer_size = output_buffer_size;
params.no_active_sensing = 1;
- err = snd_rawmidi_output_params(msynth->output_rfile.output, &params);
+ err = snd_rawmidi_output_params(rfile.output, &params);
if (err < 0) {
- snd_rawmidi_kernel_release(&msynth->output_rfile);
+ snd_rawmidi_kernel_release(&rfile);
return err;
}
snd_midi_event_reset_decode(msynth->parser);
+ scoped_guard(spinlock_irqsave, &msynth->output_lock)
+ msynth->output_rfile = rfile;
return 0;
}
@@ -242,11 +261,19 @@ static int midisynth_use(void *private_data, struct snd_seq_port_subscribe *info
static int midisynth_unuse(void *private_data, struct snd_seq_port_subscribe *info)
{
struct seq_midisynth *msynth = private_data;
+ struct snd_rawmidi_file rfile = {};
- if (snd_BUG_ON(!msynth->output_rfile.output))
+ scoped_guard(spinlock_irqsave, &msynth->output_lock) {
+ rfile = msynth->output_rfile;
+ msynth->output_rfile = (struct snd_rawmidi_file){};
+ }
+
+ if (snd_BUG_ON(!rfile.output))
return -EINVAL;
- snd_rawmidi_drain_output(msynth->output_rfile.output);
- return snd_rawmidi_kernel_release(&msynth->output_rfile);
+
+ snd_use_lock_sync(&msynth->output_use_lock);
+ snd_rawmidi_drain_output(rfile.output);
+ return snd_rawmidi_kernel_release(&rfile);
}
/* delete given midi synth port */
generated by cgit 1.3-korg (git 2.53.0) at 2026-06-01 04:05:51 +0000