| Message ID | Pine.LNX.4.64.1101281642080.8546@pc-004.diku.dk |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Julia Lawall <julia@diku.dk> Date: Fri, 28 Jan 2011 16:43:40 +0100 (CET) > nlmsg_cancel can accept NULL as its second argument, so for similarity, > this patch extends genlmsg_cancel to be able to accept a NULL second > argument as well. > > Signed-off-by: Julia Lawall <julia@diku.dk> I did a scan of all of the cases where this interface is used, and I cannot find a situation where this capability would even be useful. The use pattern is always: hdr = genlmsg_put(skb, ...); if (!hdr) goto out; NLA_PUT_*(); NLA_PUT_*(); .... return genlmsg_end(skb, hdr); nla_put_failure: genlmsg_cancel(skb, hdr); out: return -EWHATEVER; Always, hdr will be non-NULL. We have to allocate the header first, then put the netlink attributes. Looking over users of nlmsg_cancel(), the situation seems to match identically. Therefore, it seems to me that it makes more sense to remove the NULL check from nlmsg_cancel() than to add the NULL check to genlmsg_cancel(). Thanks. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, 1 Feb 2011, David Miller wrote: > From: Julia Lawall <julia@diku.dk> > Date: Fri, 28 Jan 2011 16:43:40 +0100 (CET) > > > nlmsg_cancel can accept NULL as its second argument, so for similarity, > > this patch extends genlmsg_cancel to be able to accept a NULL second > > argument as well. > > > > Signed-off-by: Julia Lawall <julia@diku.dk> > > I did a scan of all of the cases where this interface is used, and > I cannot find a situation where this capability would even be useful. > > The use pattern is always: > > hdr = genlmsg_put(skb, ...); > if (!hdr) > goto out; > > NLA_PUT_*(); > NLA_PUT_*(); > .... > > return genlmsg_end(skb, hdr); > > nla_put_failure: > genlmsg_cancel(skb, hdr); > out: > return -EWHATEVER; > > Always, hdr will be non-NULL. > > We have to allocate the header first, then put the netlink > attributes. > > Looking over users of nlmsg_cancel(), the situation seems to > match identically. > > Therefore, it seems to me that it makes more sense to remove > the NULL check from nlmsg_cancel() than to add the NULL check > to genlmsg_cancel(). I saw lots of cases that could be done like this, but were not; they had goto nla_put_failure instead. I will double check. julia -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, 1 Feb 2011, David Miller wrote: > From: Julia Lawall <julia@diku.dk> > Date: Fri, 28 Jan 2011 16:43:40 +0100 (CET) > > > nlmsg_cancel can accept NULL as its second argument, so for similarity, > > this patch extends genlmsg_cancel to be able to accept a NULL second > > argument as well. > > > > Signed-off-by: Julia Lawall <julia@diku.dk> > > I did a scan of all of the cases where this interface is used, and > I cannot find a situation where this capability would even be useful. > > The use pattern is always: > > hdr = genlmsg_put(skb, ...); > if (!hdr) > goto out; > > NLA_PUT_*(); > NLA_PUT_*(); > .... > > return genlmsg_end(skb, hdr); > > nla_put_failure: > genlmsg_cancel(skb, hdr); > out: > return -EWHATEVER; This pattern occurred in eg: net/netlabel/netlabel_unlabeled.c in the function netlbl_unlabel_staticlist_gen and in other netlabel code, as well as in net/wireless/nl80211.c, but with the function nl80211hdr_put instead of genlmsg_put. I submitted patches for all of these cases, so that is perhaps why you don't see them. But someone suggested to change genlmsg_cancel as well, to be as permissive as nlmsg_cancel. For nlmsg_cancel, there are two occurrences in net/netfilter/nf_conntrack_netlink.c where nlmsg_cancel is reachable with the second argument NULL. For nlmsg_cancel the ability to accept NULL as a second argument comes from the fact that it only calls nlmsg_trim, which does nothing if NULL is the second argument. nlmsg_trim is also called by nla_nest_cancel. There are many calls to nla_nest_cancel with NULL as the second argument in the directory net/sched, for example in the function gred_dump in net/sched/sch_gred.c. net/sched also contains a call to nlmsg_trim with NULL as the second argument, in the function flow_dump, in net/sched/cls_flow.c. The whole thing seems somewhat sloppy. I'm sure that all of the above-cited occurrences could be rewritten as outlined above to skip over the cancel/trim function. julia -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Julia Lawall <julia@diku.dk> Date: Wed, 2 Feb 2011 07:17:29 +0100 (CET) > This pattern occurred in eg: > > net/netlabel/netlabel_unlabeled.c > > in the function netlbl_unlabel_staticlist_gen and in other netlabel code, > as well as in net/wireless/nl80211.c, but with the function nl80211hdr_put > instead of genlmsg_put. I submitted patches for all of these cases, so > that is perhaps why you don't see them. But someone suggested to change > genlmsg_cancel as well, to be as permissive as nlmsg_cancel. > > For nlmsg_cancel, there are two occurrences in > net/netfilter/nf_conntrack_netlink.c where nlmsg_cancel is reachable with > the second argument NULL. > > For nlmsg_cancel the ability to accept NULL as a second argument comes > from the fact that it only calls nlmsg_trim, which does nothing if NULL is > the second argument. nlmsg_trim is also called by nla_nest_cancel. There > are many calls to nla_nest_cancel with NULL as the second argument in the > directory net/sched, for example in the function gred_dump in > net/sched/sch_gred.c. net/sched also contains a call to nlmsg_trim with > NULL as the second argument, in the function flow_dump, in > net/sched/cls_flow.c. > > The whole thing seems somewhat sloppy. I'm sure that all of the > above-cited occurrences could be rewritten as outlined above to skip over > the cancel/trim function. Thanks for the analysis Julia. I think the only safe thing to do in net-2.6 and -stable is to add the NULL check to genlmsg_cancel() as your patch did. I we later want to move things such that, consistently, we never call *nlmsg_cancel() with a NULL second arg, that's fine. I'll apply your genlmsg_cancel() patch, thanks Julia. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/net/genetlink.h b/include/net/genetlink.h index 8a64b81..b4c7c1c 100644 --- a/include/net/genetlink.h +++ b/include/net/genetlink.h @@ -195,7 +195,8 @@ static inline int genlmsg_end(struct sk_buff *skb, void *hdr) */ static inline void genlmsg_cancel(struct sk_buff *skb, void *hdr) { - nlmsg_cancel(skb, hdr - GENL_HDRLEN - NLMSG_HDRLEN); + if (hdr) + nlmsg_cancel(skb, hdr - GENL_HDRLEN - NLMSG_HDRLEN); } /**
nlmsg_cancel can accept NULL as its second argument, so for similarity, this patch extends genlmsg_cancel to be able to accept a NULL second argument as well. Signed-off-by: Julia Lawall <julia@diku.dk> --- include/net/genetlink.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html