Messages in this thread | | | Date | Thu, 29 Jul 2004 01:24:53 +0200 | From | Johannes Stezenbach <> | Subject | Re: 2.6.8-rc2-mm1 |
| |
On Wed, Jul 28, 2004 at 11:44:23PM +0100, viro@parcelfarce.linux.theplanet.co.uk wrote: > On Thu, Jul 29, 2004 at 12:24:55AM +0200, Johannes Stezenbach wrote: > > Signed-off-by: Johannes Stezenbach <js@convergence.de> > > > > --- linux-2.6.8-rc2/drivers/media/dvb/dvb-core/dvb_functions.c.orig 2004-07-29 00:19:50.000000000 +0200 > > +++ linux-2.6.8-rc2/drivers/media/dvb/dvb-core/dvb_functions.c 2004-07-29 00:20:05.000000000 +0200 > > @@ -36,7 +36,7 @@ int dvb_usercopy(struct inode *inode, st > > /* Copy arguments into temp kernel buffer */ > > switch (_IOC_DIR(cmd)) { > > case _IOC_NONE: > > - parg = NULL; > > + parg = (void *) arg; > > Mind explaining why it is the right thing to do? You are creating a kernel > pointer out of value passed to you by userland and feed it to a function > that expects a kernel pointer. Which is an invitation for trouble - if > it ends up dereferenced, we are screwed and won't notice that.
This is a hack introduced by someone years ago. The "pointer" is actually an integer argument, e.g. in include/linux/dvb/audio.h:
#define AUDIO_SET_MUTE _IO('o', 6)
actually takes an integer argument (!0 mute, 0 unmute), so one can write
if (ioctl(fd, AUDIO_SET_MUTE, 1) == -1) perror("mute");
It is unusual (maybe even wrong?), but we cannot change it without losing binary API compatibility. However, I see that sparse might flag this as a possible bug :-(
Johannes - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |