From 53b56da83d7899de375a9de153fd7f5397de85e6 Mon Sep 17 00:00:00 2001 From: Liping Zhang Date: Mon, 17 Apr 2017 21:18:57 +0800 Subject: netfilter: ctnetlink: make it safer when updating ct->status After converting to use rcu for conntrack hash, one CPU may update the ct->status via ctnetlink, while another CPU may process the packets and update the ct->status. So the non-atomic operation "ct->status |= status;" via ctnetlink becomes unsafe, and this may clear the IPS_DYING_BIT bit set by another CPU unexpectedly. For example: CPU0 CPU1 ctnetlink_change_status __nf_conntrack_find_get old = ct->status nf_ct_gc_expired - nf_ct_kill - test_and_set_bit(IPS_DYING_BIT new = old | status; - ct->status = new; <-- oops, _DYING_ is cleared! Now using a series of atomic bit operation to solve the above issue. Also note, user shouldn't set IPS_TEMPLATE, IPS_SEQ_ADJUST directly, so make these two bits be unchangable too. If we set the IPS_TEMPLATE_BIT, ct will be freed by nf_ct_tmpl_free, but actually it is alloced by nf_conntrack_alloc. If we set the IPS_SEQ_ADJUST_BIT, this may cause the NULL pointer deference, as the nfct_seqadj(ct) maybe NULL. Last, add some comments to describe the logic change due to the commit a963d710f367 ("netfilter: ctnetlink: Fix regression in CTA_STATUS processing"), which makes me feel a little confusing. Fixes: 76507f69c44e ("[NETFILTER]: nf_conntrack: use RCU for conntrack hash") Signed-off-by: Liping Zhang Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conntrack_netlink.c | 33 ++++++++++++++++++++++++--------- 1 file changed, 24 insertions(+), 9 deletions(-) (limited to 'net/netfilter') diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c index e5f97777b1f4..86deed6a8db4 100644 --- a/net/netfilter/nf_conntrack_netlink.c +++ b/net/netfilter/nf_conntrack_netlink.c @@ -1419,6 +1419,24 @@ ctnetlink_parse_nat_setup(struct nf_conn *ct, } #endif +static void +__ctnetlink_change_status(struct nf_conn *ct, unsigned long on, + unsigned long off) +{ + unsigned int bit; + + /* Ignore these unchangable bits */ + on &= ~IPS_UNCHANGEABLE_MASK; + off &= ~IPS_UNCHANGEABLE_MASK; + + for (bit = 0; bit < __IPS_MAX_BIT; bit++) { + if (on & (1 << bit)) + set_bit(bit, &ct->status); + else if (off & (1 << bit)) + clear_bit(bit, &ct->status); + } +} + static int ctnetlink_change_status(struct nf_conn *ct, const struct nlattr * const cda[]) { @@ -1438,10 +1456,7 @@ ctnetlink_change_status(struct nf_conn *ct, const struct nlattr * const cda[]) /* ASSURED bit can only be set */ return -EBUSY; - /* Be careful here, modifying NAT bits can screw up things, - * so don't let users modify them directly if they don't pass - * nf_nat_range. */ - ct->status |= status & ~(IPS_NAT_DONE_MASK | IPS_NAT_MASK); + __ctnetlink_change_status(ct, status, 0); return 0; } @@ -1628,7 +1643,7 @@ ctnetlink_change_seq_adj(struct nf_conn *ct, if (ret < 0) return ret; - ct->status |= IPS_SEQ_ADJUST; + set_bit(IPS_SEQ_ADJUST_BIT, &ct->status); } if (cda[CTA_SEQ_ADJ_REPLY]) { @@ -1637,7 +1652,7 @@ ctnetlink_change_seq_adj(struct nf_conn *ct, if (ret < 0) return ret; - ct->status |= IPS_SEQ_ADJUST; + set_bit(IPS_SEQ_ADJUST_BIT, &ct->status); } return 0; @@ -2289,10 +2304,10 @@ ctnetlink_update_status(struct nf_conn *ct, const struct nlattr * const cda[]) /* This check is less strict than ctnetlink_change_status() * because callers often flip IPS_EXPECTED bits when sending * an NFQA_CT attribute to the kernel. So ignore the - * unchangeable bits but do not error out. + * unchangeable bits but do not error out. Also user programs + * are allowed to clear the bits that they are allowed to change. */ - ct->status = (status & ~IPS_UNCHANGEABLE_MASK) | - (ct->status & IPS_UNCHANGEABLE_MASK); + __ctnetlink_change_status(ct, status, ~status); return 0; } -- cgit v1.2.3