From 8670c3a55e91cb27a4b4d4d4c4fa35b0149e1abf Mon Sep 17 00:00:00 2001 From: Patrick McHardy Date: Tue, 3 Mar 2015 20:04:18 +0000 Subject: [PATCH] netfilter: nf_tables: fix transaction race condition A race condition exists in the rule transaction code for rules that get added and removed within the same transaction. The new rule starts out as inactive in the current and active in the next generation and is inserted into the ruleset. When it is deleted, it is additionally set to inactive in the next generation as well. On commit the next generation is begun, then the actions are finalized. For the new rule this would mean clearing out the inactive bit for the previously current, now next generation. However nft_rule_clear() clears out the bits for *both* generations, activating the rule in the current generation, where it should be deactivated due to being deleted. The rule will thus be active until the deletion is finalized, removing the rule from the ruleset. Similarly, when aborting a transaction for the same case, the undo of insertion will remove it from the RCU protected rule list, the deletion will clear out all bits. However until the next RCU synchronization after all operations have been undone, the rule is active on CPUs which can still see the rule on the list. Generally, there may never be any modifications of the current generations' inactive bit since this defeats the entire purpose of atomicity. Change nft_rule_clear() to only touch the next generations bit to fix this. Signed-off-by: Patrick McHardy Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_tables_api.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c index a8c94620f20e..6fb532bf0fdb 100644 --- a/net/netfilter/nf_tables_api.c +++ b/net/netfilter/nf_tables_api.c @@ -227,7 +227,7 @@ nft_rule_deactivate_next(struct net *net, struct nft_rule *rule) static inline void nft_rule_clear(struct net *net, struct nft_rule *rule) { - rule->genmask = 0; + rule->genmask &= ~(1 << gencursor_next(net)); } static int -- 2.20.1