ALSA: line6: Fix endless MIDI read loop

The MIDI input event parser of the LINE6 driver may enter into an
endless loop when the unexpected data sequence is given, as it tries
to continue the secondary bytes without termination.  Also, when the
input data is too short, the parser returns a negative error, while
the caller doesn't handle it properly.  This would lead to the
unexpected behavior as well.

This patch addresses those issues by checking the return value
correctly and handling the one-byte event in the parser properly.

The bug was reported by syzkaller.

Reported-by: syzbot+cce32521ee0a824c21f7@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/000000000000033087059f8f8fa3@google.com
Link: https://lore.kernel.org/r/20200309095922.30269-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/line6/driver.c b/sound/usb/line6/driver.c
index b5a3f754a4f13e145e42172be822a2a4a1190dc7..4f096685ed6543fd892d473d2f02896ed292260a 100644 (file)
--- a/sound/usb/line6/driver.c
+++ b/sound/usb/line6/driver.c
@@ -305,7 +305,7 @@ static void line6_data_received(struct urb *urb)
                                line6_midibuf_read(mb, line6->buffer_message,
                                                LINE6_MIDI_MESSAGE_MAXLEN);
 
-                       if (done == 0)
+                       if (done <= 0)
                                break;
 
                        line6->message_length = done;

diff --git a/sound/usb/line6/midibuf.c b/sound/usb/line6/midibuf.c
index 8d6eefa0d9362a1c6c64d7b5cac955f9bc94bc5c..6a70463f82c4efcbd533c192844e072cae497cc2 100644 (file)
--- a/sound/usb/line6/midibuf.c
+++ b/sound/usb/line6/midibuf.c
@@ -159,7 +159,7 @@ int line6_midibuf_read(struct midi_buffer *this, unsigned char *data,
                        int midi_length_prev =
                            midibuf_message_length(this->command_prev);
 
-                       if (midi_length_prev > 0) {
+                       if (midi_length_prev > 1) {
                                midi_length = midi_length_prev - 1;
                                repeat = 1;
                        } else