Re: [PATCH v2] sound/oss: remove offset from load_patch callbacks
From: Takashi Iwai
Date: Wed Mar 23 2011 - 10:47:15 EST
At Wed, 23 Mar 2011 10:06:22 -0400,
Dan Rosenberg wrote:
> On Wed, 2011-03-23 at 14:59 +0100, Takashi Iwai wrote:
> > At Wed, 23 Mar 2011 09:47:22 -0400,
> > Dan Rosenberg wrote:
> > > --- a/sound/oss/midi_synth.c
> > > +++ b/sound/oss/midi_synth.c
> > > @@ -508,16 +506,15 @@ midi_synth_load_patch(int dev, int format, const char __user *addr,
> > > * been transferred already.
> > > */
> > >
> > > - if(copy_from_user(&((char *) &sysex)[offs], &(addr)[offs], hdr_size - offs))
> > > + if (copy_from_user(&sysex, addr, hdr_size))
> > Please correct the comment in the above as well.
> > With this change, the transfer is no longer partial.
> Will do.
> > > --- a/sound/oss/opl3.c
> > > +++ b/sound/oss/opl3.c
> > ...
> > > @@ -834,7 +834,7 @@ static int opl3_load_patch(int dev, int format, const char __user *addr,
> > > * What the fuck is going on here? We leave junk in the beginning
> > > * of ins and then check the field pretty close to that beginning?
> > > */
> > > - if(copy_from_user(&((char *) &ins)[offs], addr + offs, sizeof(ins) - offs))
> > > + if (copy_from_user(&ins, addr, sizeof(ins)))
> > Ditto.
> > > return -EFAULT;
> > >
> > > if (ins.channel < 0 || ins.channel >= SBFM_MAXINSTR)
> > > diff --git a/sound/oss/sequencer.c b/sound/oss/sequencer.c
> > > index 5ea1098..2e842cb 100644
> > > --- a/sound/oss/sequencer.c
> > > +++ b/sound/oss/sequencer.c
> > > @@ -241,7 +241,7 @@ int sequencer_write(int dev, struct file *file, const char __user *buf, int coun
> > > return -ENXIO;
> > >
> > > fmt = (*(short *) &event_rec) & 0xffff;
> > > - err = synth_devs[dev]->load_patch(dev, fmt, buf, p + 4, c, 0);
> > > + err = synth_devs[dev]->load_patch(dev, fmt, buf, c, 0);
> > The address must be "buf + p + 4" instead of "buf", when you omit the
> > offset argument.
> Are you sure? Previously, the copy of the header was from (buf + p + 4)
> to (dst + p + 4) with length (hdr_size - (p + 4)), and now the copy is
> from buf to dst with length hdr_size. If I do as you suggest, then the
> copy will be from (buf + p + 4) to dst for the header.
Hm, looking back to the original code, I found that I almost forgot
the trickiness of patch-loading in OSS. Actually, it should be like:
err = synth_devs[dev]->load_patch(dev, fmt, buf + p, c, 0);
Here, "buf + p" points to the 4-byte event packet that is being
processed. And, these 4 bytes are also shared with the first 4 bytes
of struct sysex_info or struct sbi_instrument. That is,
sysex_info.key == fmt and sysex_info.device_no == dev.
The problem in the original code is that it tries to avoid extra
copying of these 4 bytes, but failed to handle correctly, by
misinterpreting offs parameter.
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