On Fri, 28 Jan 2011, Paul Moore wrote: > On Fri, 2011-01-28 at 15:58 +0100, Julia Lawall wrote: > > On Fri, 28 Jan 2011, Paul Moore wrote: > > > > > On Fri, 2011-01-28 at 15:17 +0100, Julia Lawall wrote: > > > > genlmsg_cancel subtracts some constants from its second argument before > > > > calling nlmsg_cancel. nlmsg_cancel then calls nlmsg_trim on the same > > > > arguments. nlmsg_trim tests for NULL before doing any computation, but a > > > > NULL second argument to genlmsg_cancel is no longer NULL due to the initial > > > > subtraction. Nothing else happens in this execution, so the call to > > > > genlmsg_cancel is simply unnecessary in this case. > > > > > > > > The semantic match that finds this problem is as follows: > > > > (http://coccinelle.lip6.fr/) > > > > > > > > // <smpl> > > > > @@ > > > > expression data; > > > > @@ > > > > > > > > if (data == NULL) { ... > > > > * genlmsg_cancel(..., data); > > > > ... > > > > return ...; > > > > } > > > > // </smpl> > > > > > > > > Signed-off-by: Julia Lawall <julia@xxxxxxx> > > > > > > In all of the cases below, these functions are called multiple times to > > > generate data chunks (additional netlink attributes) which are appended > > > to an existing skbuff. I believe that the calls to genlmsg_cancel() are > > > still needed to help cleanup in the case where the functions fail on the > > > Nth call. > > > > > > If I'm wrong, feel free to enlighten me. > > > > Perhaps something is needed, but I don't see how the current code can > > work. The call is genlmsg_cancel(cb_arg->skb, NULL) in each case. > > Ah yes, you're right. You will have to forgive me as it has been quite > a while since I have looked at NetLabel's netlink code. > > You also might consider putting a NULL check in genlmsg_cancel() similar > to the check nlmsg_trim(); that seems like a worthwhile addition. OK, I'll do that. julia -- To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
