ALSA: line6: Fix endless MIDI read loop

commit d683469b3c93d7e2afd39e6e1970f24700eb7a68 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/sound/usb/line6/driver.c b/sound/usb/line6/driver.c
index 09189249d0d19362b79b9327ff000dc5f83428a7..ea3a9bd05e687ec7ae95635783de4babba80c2e4 100644 (file)
--- a/sound/usb/line6/driver.c
+++ b/sound/usb/line6/driver.c
@@ -306,7 +306,7 @@ 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 36a610ba342ec190b7b44c4a842fe93251380241..c931d48801ebed6626fdbfd0491d672d29c917b3 100644 (file)
--- a/sound/usb/line6/midibuf.c
+++ b/sound/usb/line6/midibuf.c
@@ -163,7 +163,7 @@ 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