| Message ID | 20220823072717.1706-1-tiwai@suse.de (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 22dec134dbfa825b963f8a1807ad19b943e46a56 |
| Headers | show |
| Series | [1/2] ALSA: seq: oss: Fix data-race for max_midi_devs access | expand |
We have tested this patch and confirm it eliminates the race we observed on max_mididev. Best, Gabe On Tue, Aug 23, 2022 at 3:27 AM Takashi Iwai <tiwai@suse.de> wrote: > ALSA OSS sequencer refers to a global variable max_midi_devs at > creating a new port, storing it to its own field. Meanwhile this > variable may be changed by other sequencer events at > snd_seq_oss_midi_check_exit_port() in parallel, which may cause a data > race. > > OTOH, this data race itself is almost harmless, as the access to the > MIDI device is done via get_mdev() and it's protected with a refcount, > hence its presence is guaranteed. > > Though, it's sill better to address the data-race from the code sanity > POV, and this patch adds the proper spinlock for the protection. > > Reported-by: Abhishek Shah <abhishek.shah@columbia.edu> > Cc: <stable@vger.kernel.org> > Link: > https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_r_CAEHB2493pZRXs863w58QWnUTtv3HHfg85aYhLn5HJHCwxqtHQg-40mail.gmail.com&d=DwIDAg&c=009klHSCxuh5AI1vNQzSO0KGjl4nbi2Q0M1QLJX9BeE&r=EyAJYRJu01oaAhhVVY3o8zKgZvacDAXd_PNRtaqACCo&m=CxIkVQqIvngOHaCRT98C_jGfJo6SNC38iwxKsCn-3yU1vAYynFqC_nB4PAgPegMm&s=B8XPQtfIHmyV0Z-NAEtd5FG1Indh15kFF_yJWOMLnz4&e= > > Signed-off-by: Takashi Iwai <tiwai@suse.de> > --- > sound/core/seq/oss/seq_oss_midi.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/sound/core/seq/oss/seq_oss_midi.c > b/sound/core/seq/oss/seq_oss_midi.c > index 1e3bf086f867..07efb38f58ac 100644 > --- a/sound/core/seq/oss/seq_oss_midi.c > +++ b/sound/core/seq/oss/seq_oss_midi.c > @@ -270,7 +270,9 @@ snd_seq_oss_midi_clear_all(void) > void > snd_seq_oss_midi_setup(struct seq_oss_devinfo *dp) > { > + spin_lock_irq(®ister_lock); > dp->max_mididev = max_midi_devs; > + spin_unlock_irq(®ister_lock); > } > > /* > -- > 2.35.3 > >
diff --git a/sound/core/seq/oss/seq_oss_midi.c b/sound/core/seq/oss/seq_oss_midi.c index 1e3bf086f867..07efb38f58ac 100644 --- a/sound/core/seq/oss/seq_oss_midi.c +++ b/sound/core/seq/oss/seq_oss_midi.c @@ -270,7 +270,9 @@ snd_seq_oss_midi_clear_all(void) void snd_seq_oss_midi_setup(struct seq_oss_devinfo *dp) { + spin_lock_irq(®ister_lock); dp->max_mididev = max_midi_devs; + spin_unlock_irq(®ister_lock); } /*
ALSA OSS sequencer refers to a global variable max_midi_devs at creating a new port, storing it to its own field. Meanwhile this variable may be changed by other sequencer events at snd_seq_oss_midi_check_exit_port() in parallel, which may cause a data race. OTOH, this data race itself is almost harmless, as the access to the MIDI device is done via get_mdev() and it's protected with a refcount, hence its presence is guaranteed. Though, it's sill better to address the data-race from the code sanity POV, and this patch adds the proper spinlock for the protection. Reported-by: Abhishek Shah <abhishek.shah@columbia.edu> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/CAEHB2493pZRXs863w58QWnUTtv3HHfg85aYhLn5HJHCwxqtHQg@mail.gmail.com Signed-off-by: Takashi Iwai <tiwai@suse.de> --- sound/core/seq/oss/seq_oss_midi.c | 2 ++ 1 file changed, 2 insertions(+)