On Tue, Jul 18, 2023 at 3:29 PM Stanislav Fomichev <sdf@xxxxxxxxxx> wrote: > > On Tue, Jul 18, 2023 at 11:22 AM Yan Zhai <yan@xxxxxxxxxxxxxx> wrote: > > > > skb_do_redirect handles returns error code from both rx and tx path. > > The tx path codes are special, e.g. NET_XMIT_CN: they are > > non-negative, and can conflict with LWTUNNEL_XMIT_xxx values. Directly > > returning such code can cause unexpected behavior. We found at least > > one bug that will panic the kernel through KASAN report when we > > accidentally redirect packets to a down or carrier-down device at lwt > > xmit hook: > > > > https://gist.github.com/zhaiyan920/8fbac245b261fe316a7ef04c9b1eba48 > > > > Above bug is hit because NET_XMIT_CN is returned by noop_qdisc of the > > down device, and it propagates from dev_queue_xmit all way to the lwt > > logic. Although skb has been freed by the qdisc, it still continues to > > neighbor subsystem and triggers the bug. > > > > This change converts the tx code to proper errors that lwt can consume. > > > > Reported-by: Jordan Griege <jgriege@xxxxxxxxxxxxxx> > > Signed-off-by: Yan Zhai <yan@xxxxxxxxxxxxxx> > > --- > > net/core/filter.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/net/core/filter.c b/net/core/filter.c > > index 06ba0e56e369..c9cc501ecdc0 100644 > > --- a/net/core/filter.c > > +++ b/net/core/filter.c > > @@ -2129,6 +2129,11 @@ static inline int __bpf_tx_skb(struct net_device *dev, struct sk_buff *skb) > > ret = dev_queue_xmit(skb); > > dev_xmit_recursion_dec(); > > > > + // We should not return NET_XMIT_xxx here since it will conflict with > > + // LWTUNNEL_XMIT_xxx values. Convert the return value to errno instead. > > C++ comments; should be /* */. But, also, maybe they are not really needed? > *facepalm* yes I think we can remove them since the commit message already covers it... > ret = dev_queue_xmit(skb); > if (ret) > ret = net_xmit_errno(ret); > > We have a bunch of places with the pattern like this, so probably can > do the same here? > Personally I like an explicit name better, since not all the return codes use 0 to signal success, e.g. XDP_PASS, TC_ACT_PIPE. But I'd leave that for future improvements now that all other places use 0 on this. thanks Yan > > + if (unlikely(ret != NET_XMIT_SUCCESS)) > > + ret = net_xmit_errno(ret); > > + > > return ret; > > } > > > > -- > > 2.30.2 > > -- Yan
