From: Florian Westphal <f...@strlen.de> Date: Sat, 12 Mar 2016 11:14:42 +0100
> Zefir Kurtisi reported kernel panic with an openwrt specific patch. > However, it turns out that mainline has a similar bug waiting to happen. > > Once NF_HOOK() returns the skb is in undefined state and must not be > used. Moreover, the okfn must consume the skb to support async > processing (NF_QUEUE). > > Current okfn in this spot doesn't consume it and caller assumes that > NF_HOOK return value tells us if skb was freed or not, but thats wrong. > > It "works" because no in-tree user registers a NFPROTO_BRIDGE hook at > LOCAL_IN that returns STOLEN or NF_QUEUE verdicts. > > Once we add NF_QUEUE support for nftables bridge this will break -- > NF_QUEUE holds the skb for async processing, caller will erronoulsy > return RX_HANDLER_PASS and on reinject netfilter will access free'd skb. > > Fix this by pushing skb up the stack in the okfn instead. > > NB: It also seems dubious to use LOCAL_IN while bypassing PRE_ROUTING > completely in this case but this is how its been forever so it seems > preferable to not change this. > > Cc: Felix Fietkau <n...@openwrt.org> > Cc: Zefir Kurtisi <zefir.kurt...@neratec.com> > Signed-off-by: Florian Westphal <f...@strlen.de> Technically this is a netfilter change, but I'll apply it directly to my tree, thanks Florian.
