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netfilter: ctnetlink: make it safer when updating ct->status

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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 a963d710f3 ("netfilter: ctnetlink: Fix regression in CTA_STATUS
processing"), which makes me feel a little confusing.

Fixes: 76507f69c4 ("[NETFILTER]: nf_conntrack: use RCU for conntrack hash")
Signed-off-by: Liping Zhang <zlpnobody@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Liping Zhang
2017-04-17 21:18:57 +08:00
committed by Pablo Neira Ayuso
parent 88be4c09d9
commit 53b56da83d
2 changed files with 33 additions and 13 deletions
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13
include/uapi/linux/netfilter/nf_conntrack_common.h
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@@ -82,10 +82,6 @@ enum ip_conntrack_status {
IPS_DYING_BIT = 9,
IPS_DYING = (1 << IPS_DYING_BIT),
/* Bits that cannot be altered from userland. */
IPS_UNCHANGEABLE_MASK = (IPS_NAT_DONE_MASK | IPS_NAT_MASK |
IPS_EXPECTED | IPS_CONFIRMED | IPS_DYING),
/* Connection has fixed timeout. */
IPS_FIXED_TIMEOUT_BIT = 10,
IPS_FIXED_TIMEOUT = (1 << IPS_FIXED_TIMEOUT_BIT),
@@ -101,6 +97,15 @@ enum ip_conntrack_status {
/* Conntrack got a helper explicitly attached via CT target. */
IPS_HELPER_BIT = 13,
IPS_HELPER = (1 << IPS_HELPER_BIT),
/* Be careful here, modifying these bits can make things messy,
* so don't let users modify them directly.
*/
IPS_UNCHANGEABLE_MASK = (IPS_NAT_DONE_MASK | IPS_NAT_MASK |
IPS_EXPECTED | IPS_CONFIRMED | IPS_DYING |
IPS_SEQ_ADJUST | IPS_TEMPLATE),
__IPS_MAX_BIT = 14,
};
/* Connection tracking event types */