From: Florian Westphal fw@strlen.de
[ Upstream commit c2577862eeb0be94f151f2f1fff662b028061b00 ]
When br_netfilter module is loaded, skbs may be diverted to the ipv4/ipv6 hooks, just like as if we were routing.
Unfortunately, bridge filter hooks with priority 0 may be skipped in this case.
Example: 1. an nftables bridge ruleset is loaded, with a prerouting hook that has priority 0. 2. interface is added to the bridge. 3. no tcp packet is ever seen by the bridge prerouting hook. 4. flush the ruleset 5. load the bridge ruleset again. 6. tcp packets are processed as expected.
After 1) the only registered hook is the bridge prerouting hook, but its not called yet because the bridge hasn't been brought up yet.
After 2), hook order is: 0 br_nf_pre_routing // br_netfilter internal hook 0 chain bridge f prerouting // nftables bridge ruleset
The packet is diverted to br_nf_pre_routing. If call-iptables is off, the nftables bridge ruleset is called as expected.
But if its enabled, br_nf_hook_thresh() will skip it because it assumes that all 0-priority hooks had been called previously in bridge context.
To avoid this, check for the br_nf_pre_routing hook itself, we need to resume directly after it, even if this hook has a priority of 0.
Unfortunately, this still results in different packet flow. With this fix, the eval order after in 3) is: 1. br_nf_pre_routing 2. ip(6)tables (if enabled) 3. nftables bridge
but after 5 its the much saner: 1. nftables bridge 2. br_nf_pre_routing 3. ip(6)tables (if enabled)
Unfortunately I don't see a solution here: It would be possible to move br_nf_pre_routing to a higher priority so that it will be called later in the pipeline, but this also impacts ebtables evaluation order, and would still result in this very ordering problem for all nftables-bridge hooks with the same priority as the br_nf_pre_routing one.
Searching back through the git history I don't think this has ever behaved in any other way, hence, no fixes-tag.
Reported-by: Radim Hrazdil rhrazdil@redhat.com Signed-off-by: Florian Westphal fw@strlen.de Signed-off-by: Pablo Neira Ayuso pablo@netfilter.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/bridge/br_netfilter_hooks.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-)
diff --git a/net/bridge/br_netfilter_hooks.c b/net/bridge/br_netfilter_hooks.c index 4b9d1d6bbf6f..55c7cdf5e7b8 100644 --- a/net/bridge/br_netfilter_hooks.c +++ b/net/bridge/br_netfilter_hooks.c @@ -1001,9 +1001,24 @@ int br_nf_hook_thresh(unsigned int hook, struct net *net, return okfn(net, sk, skb);
ops = nf_hook_entries_get_hook_ops(e); - for (i = 0; i < e->num_hook_entries && - ops[i]->priority <= NF_BR_PRI_BRNF; i++) - ; + for (i = 0; i < e->num_hook_entries; i++) { + /* These hooks have already been called */ + if (ops[i]->priority < NF_BR_PRI_BRNF) + continue; + + /* These hooks have not been called yet, run them. */ + if (ops[i]->priority > NF_BR_PRI_BRNF) + break; + + /* take a closer look at NF_BR_PRI_BRNF. */ + if (ops[i]->hook == br_nf_pre_routing) { + /* This hook diverted the skb to this function, + * hooks after this have not been run yet. + */ + i++; + break; + } + }
nf_hook_state_init(&state, hook, NFPROTO_BRIDGE, indev, outdev, sk, net, okfn);