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Florian Westphal ad88b7a6aa netfilter: ecache: don't look for ecache extension on dying/unconfirmed conntracks
syzbot reported following splat:
BUG: KASAN: use-after-free in __nf_ct_ext_exist
include/net/netfilter/nf_conntrack_extend.h:53 [inline]
BUG: KASAN: use-after-free in nf_ct_deliver_cached_events+0x5c3/0x6d0
net/netfilter/nf_conntrack_ecache.c:205
nf_conntrack_confirm include/net/netfilter/nf_conntrack_core.h:65 [inline]
nf_confirm+0x3d8/0x4d0 net/netfilter/nf_conntrack_proto.c:154
[..]

While there is no reproducer yet, the syzbot report contains one
interesting bit of information:

Freed by task 27585:
[..]
 kfree+0x10a/0x2c0 mm/slab.c:3757
 nf_ct_ext_destroy+0x2ab/0x2e0 net/netfilter/nf_conntrack_extend.c:38
 nf_conntrack_free+0x8f/0xe0 net/netfilter/nf_conntrack_core.c:1418
 destroy_conntrack+0x1a2/0x270 net/netfilter/nf_conntrack_core.c:626
 nf_conntrack_put include/linux/netfilter/nf_conntrack_common.h:31 [inline]
 nf_ct_resolve_clash net/netfilter/nf_conntrack_core.c:915 [inline]
 ^^^^^^^^^^^^^^^^^^^
 __nf_conntrack_confirm+0x21ca/0x2830 net/netfilter/nf_conntrack_core.c:1038
 nf_conntrack_confirm include/net/netfilter/nf_conntrack_core.h:63 [inline]
 nf_confirm+0x3e7/0x4d0 net/netfilter/nf_conntrack_proto.c:154

This is whats happening:

1. a conntrack entry is about to be confirmed (added to hash table).
2. a clash with existing entry is detected.
3. nf_ct_resolve_clash() puts skb->nfct (the "losing" entry).
4. this entry now has a refcount of 0 and is freed to SLAB_TYPESAFE_BY_RCU
   kmem cache.

skb->nfct has been replaced by the one found in the hash.
Problem is that nf_conntrack_confirm() uses the old ct:

static inline int nf_conntrack_confirm(struct sk_buff *skb)
{
 struct nf_conn *ct = (struct nf_conn *)skb_nfct(skb);
 int ret = NF_ACCEPT;

  if (ct) {
    if (!nf_ct_is_confirmed(ct))
       ret = __nf_conntrack_confirm(skb);
    if (likely(ret == NF_ACCEPT))
	nf_ct_deliver_cached_events(ct); /* This ct has refcount 0! */
  }
  return ret;
}

As of "netfilter: conntrack: free extension area immediately", we can't
access conntrack extensions in this case.

To fix this, make sure we check the dying bit presence before attempting
to get the eache extension.

Reported-by: syzbot+c7aabc9fe93e7f3637ba@syzkaller.appspotmail.com
Fixes: 2ad9d7747c ("netfilter: conntrack: free extension area immediately")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
2019-10-26 12:36:42 +02:00
arch Kbuild fixes for v5.4 2019-10-05 12:56:59 -07:00
block block: sed-opal: fix sparse warning: convert __be64 data 2019-10-03 14:21:32 -06:00
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crypto Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
Documentation net/tls: add TlsDeviceRxResync statistic 2019-10-05 16:29:00 -07:00
drivers netdevsim: create devlink and netdev instances in namespace 2019-10-05 16:34:15 -07:00
fs Merge branch 'readdir' (readdir speedup and sanity checking) 2019-10-05 12:03:27 -07:00
include netfilter: nf_tables: support for multiple devices per netdev hook 2019-10-23 13:01:34 +02:00
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kernel Kbuild fixes for v5.4 2019-10-05 12:56:59 -07:00
lib Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-10-05 08:50:15 -07:00
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mm Merge branch 'hugepage-fallbacks' (hugepatch patches from David Rientjes) 2019-09-28 14:26:47 -07:00
net netfilter: ecache: don't look for ecache extension on dying/unconfirmed conntracks 2019-10-26 12:36:42 +02:00
samples rpmsg updates for v5.4 2019-09-22 10:58:15 -07:00
scripts scripts/setlocalversion: clear local variable to make it work for sh 2019-10-05 15:29:49 +09:00
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sound sound fixes for 5.4-rc1 2019-09-24 16:46:16 -07:00
tools selftests: netfilter: add ipvs tunnel test case 2019-10-11 10:05:27 +02:00
usr kbuild: update compile-test header list for v5.4-rc2 2019-10-05 15:29:49 +09:00
virt KVM/arm fixes for 5.4, take #1 2019-10-03 12:08:50 +02:00
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CREDITS CREDITS: Update email address 2019-09-13 17:21:38 +03:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
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MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-10-05 13:37:23 -07:00
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Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
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the problems which may result by upgrading your kernel.