Commit d683469b authored Mar 09, 2020 by Takashi Iwai

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>

parent f2ecf903

sound/usb/line6/driver.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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;

sound/usb/line6/midibuf.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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

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