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![Florian Westphal](/assets/img/avatar_default.png)
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nfct has been replaced by the one found in the hash.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>
381 lines
9 KiB
C
381 lines
9 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/* Event cache for netfilter. */
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/*
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* (C) 2005 Harald Welte <laforge@gnumonks.org>
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* (C) 2005 Patrick McHardy <kaber@trash.net>
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* (C) 2005-2006 Netfilter Core Team <coreteam@netfilter.org>
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* (C) 2005 USAGI/WIDE Project <http://www.linux-ipv6.org>
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/types.h>
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#include <linux/netfilter.h>
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#include <linux/skbuff.h>
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#include <linux/vmalloc.h>
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#include <linux/stddef.h>
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#include <linux/err.h>
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#include <linux/percpu.h>
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#include <linux/kernel.h>
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#include <linux/netdevice.h>
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#include <linux/slab.h>
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#include <linux/export.h>
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#include <net/netfilter/nf_conntrack.h>
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#include <net/netfilter/nf_conntrack_core.h>
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#include <net/netfilter/nf_conntrack_ecache.h>
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#include <net/netfilter/nf_conntrack_extend.h>
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static DEFINE_MUTEX(nf_ct_ecache_mutex);
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#define ECACHE_RETRY_WAIT (HZ/10)
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#define ECACHE_STACK_ALLOC (256 / sizeof(void *))
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enum retry_state {
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STATE_CONGESTED,
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STATE_RESTART,
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STATE_DONE,
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};
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static enum retry_state ecache_work_evict_list(struct ct_pcpu *pcpu)
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{
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struct nf_conn *refs[ECACHE_STACK_ALLOC];
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enum retry_state ret = STATE_DONE;
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struct nf_conntrack_tuple_hash *h;
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struct hlist_nulls_node *n;
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unsigned int evicted = 0;
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spin_lock(&pcpu->lock);
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hlist_nulls_for_each_entry(h, n, &pcpu->dying, hnnode) {
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struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(h);
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struct nf_conntrack_ecache *e;
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if (!nf_ct_is_confirmed(ct))
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continue;
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/* This ecache access is safe because the ct is on the
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* pcpu dying list and we hold the spinlock -- the entry
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* cannot be free'd until after the lock is released.
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*
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* This is true even if ct has a refcount of 0: the
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* cpu that is about to free the entry must remove it
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* from the dying list and needs the lock to do so.
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*/
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e = nf_ct_ecache_find(ct);
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if (!e || e->state != NFCT_ECACHE_DESTROY_FAIL)
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continue;
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/* ct is in NFCT_ECACHE_DESTROY_FAIL state, this means
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* the worker owns this entry: the ct will remain valid
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* until the worker puts its ct reference.
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*/
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if (nf_conntrack_event(IPCT_DESTROY, ct)) {
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ret = STATE_CONGESTED;
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break;
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}
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e->state = NFCT_ECACHE_DESTROY_SENT;
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refs[evicted] = ct;
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if (++evicted >= ARRAY_SIZE(refs)) {
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ret = STATE_RESTART;
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break;
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}
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}
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spin_unlock(&pcpu->lock);
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/* can't _put while holding lock */
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while (evicted)
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nf_ct_put(refs[--evicted]);
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return ret;
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}
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static void ecache_work(struct work_struct *work)
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{
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struct netns_ct *ctnet =
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container_of(work, struct netns_ct, ecache_dwork.work);
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int cpu, delay = -1;
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struct ct_pcpu *pcpu;
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local_bh_disable();
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for_each_possible_cpu(cpu) {
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enum retry_state ret;
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pcpu = per_cpu_ptr(ctnet->pcpu_lists, cpu);
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ret = ecache_work_evict_list(pcpu);
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switch (ret) {
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case STATE_CONGESTED:
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delay = ECACHE_RETRY_WAIT;
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goto out;
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case STATE_RESTART:
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delay = 0;
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break;
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case STATE_DONE:
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break;
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}
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}
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out:
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local_bh_enable();
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ctnet->ecache_dwork_pending = delay > 0;
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if (delay >= 0)
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schedule_delayed_work(&ctnet->ecache_dwork, delay);
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}
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int nf_conntrack_eventmask_report(unsigned int eventmask, struct nf_conn *ct,
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u32 portid, int report)
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{
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int ret = 0;
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struct net *net = nf_ct_net(ct);
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struct nf_ct_event_notifier *notify;
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struct nf_conntrack_ecache *e;
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rcu_read_lock();
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notify = rcu_dereference(net->ct.nf_conntrack_event_cb);
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if (!notify)
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goto out_unlock;
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e = nf_ct_ecache_find(ct);
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if (!e)
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goto out_unlock;
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if (nf_ct_is_confirmed(ct)) {
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struct nf_ct_event item = {
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.ct = ct,
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.portid = e->portid ? e->portid : portid,
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.report = report
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};
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/* This is a resent of a destroy event? If so, skip missed */
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unsigned long missed = e->portid ? 0 : e->missed;
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if (!((eventmask | missed) & e->ctmask))
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goto out_unlock;
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ret = notify->fcn(eventmask | missed, &item);
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if (unlikely(ret < 0 || missed)) {
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spin_lock_bh(&ct->lock);
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if (ret < 0) {
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/* This is a destroy event that has been
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* triggered by a process, we store the PORTID
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* to include it in the retransmission.
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*/
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if (eventmask & (1 << IPCT_DESTROY)) {
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if (e->portid == 0 && portid != 0)
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e->portid = portid;
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e->state = NFCT_ECACHE_DESTROY_FAIL;
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} else {
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e->missed |= eventmask;
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}
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} else {
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e->missed &= ~missed;
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}
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spin_unlock_bh(&ct->lock);
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}
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}
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out_unlock:
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rcu_read_unlock();
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return ret;
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}
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EXPORT_SYMBOL_GPL(nf_conntrack_eventmask_report);
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/* deliver cached events and clear cache entry - must be called with locally
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* disabled softirqs */
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void nf_ct_deliver_cached_events(struct nf_conn *ct)
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{
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struct net *net = nf_ct_net(ct);
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unsigned long events, missed;
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struct nf_ct_event_notifier *notify;
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struct nf_conntrack_ecache *e;
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struct nf_ct_event item;
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int ret;
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rcu_read_lock();
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notify = rcu_dereference(net->ct.nf_conntrack_event_cb);
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if (notify == NULL)
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goto out_unlock;
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if (!nf_ct_is_confirmed(ct) || nf_ct_is_dying(ct))
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goto out_unlock;
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e = nf_ct_ecache_find(ct);
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if (e == NULL)
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goto out_unlock;
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events = xchg(&e->cache, 0);
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/* We make a copy of the missed event cache without taking
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* the lock, thus we may send missed events twice. However,
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* this does not harm and it happens very rarely. */
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missed = e->missed;
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if (!((events | missed) & e->ctmask))
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goto out_unlock;
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item.ct = ct;
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item.portid = 0;
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item.report = 0;
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ret = notify->fcn(events | missed, &item);
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if (likely(ret == 0 && !missed))
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goto out_unlock;
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spin_lock_bh(&ct->lock);
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if (ret < 0)
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e->missed |= events;
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else
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e->missed &= ~missed;
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spin_unlock_bh(&ct->lock);
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out_unlock:
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rcu_read_unlock();
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}
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EXPORT_SYMBOL_GPL(nf_ct_deliver_cached_events);
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void nf_ct_expect_event_report(enum ip_conntrack_expect_events event,
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struct nf_conntrack_expect *exp,
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u32 portid, int report)
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{
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struct net *net = nf_ct_exp_net(exp);
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struct nf_exp_event_notifier *notify;
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struct nf_conntrack_ecache *e;
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rcu_read_lock();
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notify = rcu_dereference(net->ct.nf_expect_event_cb);
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if (!notify)
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goto out_unlock;
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e = nf_ct_ecache_find(exp->master);
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if (!e)
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goto out_unlock;
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if (e->expmask & (1 << event)) {
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struct nf_exp_event item = {
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.exp = exp,
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.portid = portid,
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.report = report
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};
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notify->fcn(1 << event, &item);
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}
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out_unlock:
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rcu_read_unlock();
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}
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int nf_conntrack_register_notifier(struct net *net,
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struct nf_ct_event_notifier *new)
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{
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int ret;
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struct nf_ct_event_notifier *notify;
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mutex_lock(&nf_ct_ecache_mutex);
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notify = rcu_dereference_protected(net->ct.nf_conntrack_event_cb,
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lockdep_is_held(&nf_ct_ecache_mutex));
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if (notify != NULL) {
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ret = -EBUSY;
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goto out_unlock;
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}
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rcu_assign_pointer(net->ct.nf_conntrack_event_cb, new);
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ret = 0;
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out_unlock:
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mutex_unlock(&nf_ct_ecache_mutex);
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return ret;
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}
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EXPORT_SYMBOL_GPL(nf_conntrack_register_notifier);
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void nf_conntrack_unregister_notifier(struct net *net,
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struct nf_ct_event_notifier *new)
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{
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struct nf_ct_event_notifier *notify;
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mutex_lock(&nf_ct_ecache_mutex);
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notify = rcu_dereference_protected(net->ct.nf_conntrack_event_cb,
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lockdep_is_held(&nf_ct_ecache_mutex));
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BUG_ON(notify != new);
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RCU_INIT_POINTER(net->ct.nf_conntrack_event_cb, NULL);
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mutex_unlock(&nf_ct_ecache_mutex);
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/* synchronize_rcu() is called from ctnetlink_exit. */
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}
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EXPORT_SYMBOL_GPL(nf_conntrack_unregister_notifier);
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int nf_ct_expect_register_notifier(struct net *net,
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struct nf_exp_event_notifier *new)
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{
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int ret;
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struct nf_exp_event_notifier *notify;
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mutex_lock(&nf_ct_ecache_mutex);
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notify = rcu_dereference_protected(net->ct.nf_expect_event_cb,
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lockdep_is_held(&nf_ct_ecache_mutex));
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if (notify != NULL) {
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ret = -EBUSY;
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goto out_unlock;
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}
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rcu_assign_pointer(net->ct.nf_expect_event_cb, new);
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ret = 0;
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out_unlock:
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mutex_unlock(&nf_ct_ecache_mutex);
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return ret;
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}
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EXPORT_SYMBOL_GPL(nf_ct_expect_register_notifier);
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void nf_ct_expect_unregister_notifier(struct net *net,
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struct nf_exp_event_notifier *new)
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{
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struct nf_exp_event_notifier *notify;
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mutex_lock(&nf_ct_ecache_mutex);
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notify = rcu_dereference_protected(net->ct.nf_expect_event_cb,
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lockdep_is_held(&nf_ct_ecache_mutex));
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BUG_ON(notify != new);
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RCU_INIT_POINTER(net->ct.nf_expect_event_cb, NULL);
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mutex_unlock(&nf_ct_ecache_mutex);
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/* synchronize_rcu() is called from ctnetlink_exit. */
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}
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EXPORT_SYMBOL_GPL(nf_ct_expect_unregister_notifier);
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#define NF_CT_EVENTS_DEFAULT 1
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static int nf_ct_events __read_mostly = NF_CT_EVENTS_DEFAULT;
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static const struct nf_ct_ext_type event_extend = {
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.len = sizeof(struct nf_conntrack_ecache),
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.align = __alignof__(struct nf_conntrack_ecache),
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.id = NF_CT_EXT_ECACHE,
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};
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void nf_conntrack_ecache_pernet_init(struct net *net)
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{
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net->ct.sysctl_events = nf_ct_events;
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INIT_DELAYED_WORK(&net->ct.ecache_dwork, ecache_work);
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}
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void nf_conntrack_ecache_pernet_fini(struct net *net)
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{
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cancel_delayed_work_sync(&net->ct.ecache_dwork);
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}
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int nf_conntrack_ecache_init(void)
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{
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int ret = nf_ct_extend_register(&event_extend);
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if (ret < 0)
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pr_err("Unable to register event extension\n");
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BUILD_BUG_ON(__IPCT_MAX >= 16); /* ctmask, missed use u16 */
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return ret;
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}
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void nf_conntrack_ecache_fini(void)
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{
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nf_ct_extend_unregister(&event_extend);
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}
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