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netfilter: conntrack: fix race between nf_conntrack proc read and hash resize

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When we do "cat /proc/net/nf_conntrack", and meanwhile resize the conntrack
hash table via /sys/module/nf_conntrack/parameters/hashsize, race will
happen, because reader can observe a newly allocated hash but the old size
(or vice versa). So oops will happen like follows：

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000017
  IP: [<ffffffffa0418e21>] seq_print_acct+0x11/0x50 [nf_conntrack]
  Call Trace:
  [<ffffffffa0412f4e>] ? ct_seq_show+0x14e/0x340 [nf_conntrack]
  [<ffffffff81261a1c>] seq_read+0x2cc/0x390
  [<ffffffff812a8d62>] proc_reg_read+0x42/0x70
  [<ffffffff8123bee7>] __vfs_read+0x37/0x130
  [<ffffffff81347980>] ? security_file_permission+0xa0/0xc0
  [<ffffffff8123cf75>] vfs_read+0x95/0x140
  [<ffffffff8123e475>] SyS_read+0x55/0xc0
  [<ffffffff817c2572>] entry_SYSCALL_64_fastpath+0x1a/0xa4

It is very easy to reproduce this kernel crash.
1. open one shell and input the following cmds:
  while : ; do
    echo $RANDOM > /sys/module/nf_conntrack/parameters/hashsize
  done
2. open more shells and input the following cmds:
  while : ; do
    cat /proc/net/nf_conntrack
  done
3. just wait a monent, oops will happen soon.

The solution in this patch is based on Florian's Commit 5e3c61f981
("netfilter: conntrack: fix lookup race during hash resize"). And
add a wrapper function nf_conntrack_get_ht to get hash and hsize
suggested by Florian Westphal.

Signed-off-by: Liping Zhang <[email protected]>
Signed-off-by: Pablo Neira Ayuso <[email protected]>
This commit is contained in:
Liping Zhang 2016-07-03 13:18:43 +08:00 • committed by Pablo Neira Ayuso
commit 64b87639c9
4 changed files with 38 additions and 9 deletions
Download patch file Download diff file Expand all files Collapse all files

14
net/ipv4/netfilter/nf_conntrack_l3proto_ipv4_compat.c
View file

@ -26,6 +26,8 @@
struct ct_iter_state {
struct seq_net_private p;
struct hlist_nulls_head *hash;
unsigned int htable_size;
unsigned int bucket;
};
@ -35,10 +37,10 @@ static struct hlist_nulls_node *ct_get_first(struct seq_file *seq)
struct hlist_nulls_node *n;
for (st->bucket = 0;
st->bucket < nf_conntrack_htable_size;
st->bucket < st->htable_size;
st->bucket++) {
n = rcu_dereference(
hlist_nulls_first_rcu(&nf_conntrack_hash[st->bucket]));
hlist_nulls_first_rcu(&st->hash[st->bucket]));
if (!is_a_nulls(n))
return n;
}
@ -53,11 +55,11 @@ static struct hlist_nulls_node *ct_get_next(struct seq_file *seq,
head = rcu_dereference(hlist_nulls_next_rcu(head));
while (is_a_nulls(head)) {
if (likely(get_nulls_value(head) == st->bucket)) {
if (++st->bucket >= nf_conntrack_htable_size)
if (++st->bucket >= st->htable_size)
return NULL;
}
head = rcu_dereference(
hlist_nulls_first_rcu(&nf_conntrack_hash[st->bucket]));
hlist_nulls_first_rcu(&st->hash[st->bucket]));
}
return head;
}
@ -75,7 +77,11 @@ static struct hlist_nulls_node *ct_get_idx(struct seq_file *seq, loff_t pos)
static void *ct_seq_start(struct seq_file *seq, loff_t *pos)
__acquires(RCU)
{
struct ct_iter_state *st = seq->private;
rcu_read_lock();
nf_conntrack_get_ht(&st->hash, &st->htable_size);
return ct_get_idx(seq, *pos);
}