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SubjectRe: [PATCH] Fix potential NULL pointer dereference in echoaudio midi.
On 02/11/06, Giuliano Pochini <pochini@shiny.it> wrote:
> On Tue, 31 Oct 2006 23:26:31 +0100
> Jesper Juhl <jesper.juhl@gmail.com> wrote:
>
> > On Tuesday 31 October 2006 23:13, David Rientjes wrote:
> > > On Tue, 31 Oct 2006, Jesper Juhl wrote:
> > >
> > > > In sound/pci/echoaudio/midi.c::snd_echo_midi_output_write(), there's a risk
> > > > of dereferencing a NULL 'chip->midi_out'.
> > > > This patch contains the obvious fix as also used a bit higher up in the
> > > > same function.
> > > >
> > >
> > > How about just adding an early test:
> > > if (!chip->midi_out)
> > > goto out;
>
>
> The point of that check is to make sure is doesn't access chip->midi_out
> when (surprise!) it is NULL. This can only happen in the rare (possible?)
> case snd_echo_midi_output_close() is called while the timer handler is
> running. I have another proposal which IMHO is smp-safer that just moving
> the check. In that case we should also put a spinlock around the
> chip->midi_out=0 in the snd_echo_midi_output_close() callback.
>
>
> Signed-off-by: Giuliano Pochini <pochini@shiny.it>
>
> --- alsa-kernel/pci/echoaudio/midi.c__orig 2006-11-02 20:39:45.000000000 +0100
> +++ alsa-kernel/pci/echoaudio/midi.c 2006-11-02 20:44:22.000000000 +0100
> @@ -213,7 +213,7 @@ static void snd_echo_midi_output_write(u
> sent = bytes = 0;
> spin_lock_irqsave(&chip->lock, flags);
> chip->midi_full = 0;
> - if (chip->midi_out && !snd_rawmidi_transmit_empty(chip->midi_out)) {
> + if (!snd_rawmidi_transmit_empty(chip->midi_out)) {
> bytes = snd_rawmidi_transmit_peek(chip->midi_out, buf,
> MIDI_OUT_BUFFER_SIZE - 1);
> DE_MID(("Try to send %d bytes...\n", bytes));
> @@ -264,9 +264,11 @@ static void snd_echo_midi_output_trigger
> }
> } else {
> if (chip->tinuse) {
> - del_timer(&chip->timer);
> chip->tinuse = 0;
> + spin_unlock_irq(&chip->lock);
> + del_timer_sync(&chip->timer);
> DE_MID(("Timer removed\n"));
> + return;
> }
> }
> spin_unlock_irq(&chip->lock);
>

Fine by me.
Let's just get one of the versions pushed into -mm or mainline :)

--
Jesper Juhl <jesper.juhl@gmail.com>
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