From: Takashi Iwai tiwai@suse.de
commit 22dec134dbfa825b963f8a1807ad19b943e46a56 upstream.
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/CAEHB2493pZRXs863w58QWnUTtv3HHfg85aYhLn5HJHCwxqtHQ... Link: https://lore.kernel.org/r/20220823072717.1706-1-tiwai@suse.de Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- sound/core/seq/oss/seq_oss_midi.c | 2 ++ 1 file changed, 2 insertions(+)
--- 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); }
/*