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? 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? > + if (unlikely(ret != NET_XMIT_SUCCESS)) > + ret = net_xmit_errno(ret); > + > return ret; > } > > -- > 2.30.2 >
