From: Liping Zhang <liping.zhang@xxxxxxxxxxxxxx>
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 5e3c61f98175
("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 <liping.zhang@xxxxxxxxxxxxxx>
---
V2: Add nf_conntrack_get_ht wrapper function. I think in ____nf_conntrack_find
and nf_conntrack_tuple_taken, we can also use nf_conntrack_get_ht to simplify
the source code, but it is unrelated to this bug fix. So I'd rather take
another patch to do this thing.
include/net/netfilter/nf_conntrack_core.h | 2 ++
net/ipv4/netfilter/nf_conntrack_l3proto_ipv4_compat.c | 14 ++++++++++----
net/netfilter/nf_conntrack_core.c | 17 +++++++++++++++++
net/netfilter/nf_conntrack_standalone.c | 14 +++++++++-----
4 files changed, 38 insertions(+), 9 deletions(-)
diff --git a/include/net/netfilter/nf_conntrack_core.h b/include/net/netfilter/nf_conntrack_core.h
index 3e2f332..79d7ac5 100644
--- a/include/net/netfilter/nf_conntrack_core.h
+++ b/include/net/netfilter/nf_conntrack_core.h
@@ -51,6 +51,8 @@ bool nf_ct_invert_tuple(struct nf_conntrack_tuple *inverse,
const struct nf_conntrack_l3proto *l3proto,
const struct nf_conntrack_l4proto *l4proto);
+void nf_conntrack_get_ht(struct hlist_nulls_head **hash, unsigned int *hsize);
+
/* Find a connection corresponding to a tuple. */
struct nf_conntrack_tuple_hash *
nf_conntrack_find_get(struct net *net,
diff --git a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4_compat.c b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4_compat.c
index c6f3c40..6392371 100644
--- a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4_compat.c
+++ b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4_compat.c
@@ -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);
}
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index f204274..2d2472b 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -466,6 +466,23 @@ nf_ct_key_equal(struct nf_conntrack_tuple_hash *h,
net_eq(net, nf_ct_net(ct));
}
+/* must be called with rcu read lock held */
+void nf_conntrack_get_ht(struct hlist_nulls_head **hash, unsigned int *hsize)
+{
+ struct hlist_nulls_head *hptr;
+ unsigned int sequence, hsz;
+
+ do {
+ sequence = read_seqcount_begin(&nf_conntrack_generation);
+ hsz = nf_conntrack_htable_size;
+ hptr = nf_conntrack_hash;
+ } while (read_seqcount_retry(&nf_conntrack_generation, sequence));
+
+ *hash = hptr;
+ *hsize = hsz;
+}
+EXPORT_SYMBOL_GPL(nf_conntrack_get_ht);
+
/*
* Warning :
* - Caller must take a reference on returned object
diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
index c026c47..f430b2f 100644
--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -48,6 +48,8 @@ EXPORT_SYMBOL_GPL(print_tuple);
struct ct_iter_state {
struct seq_net_private p;
+ struct hlist_nulls_head *hash;
+ unsigned int htable_size;
unsigned int bucket;
u_int64_t time_now;
};
@@ -58,9 +60,10 @@ 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]));
+ n = rcu_dereference(
+ hlist_nulls_first_rcu(&st->hash[st->bucket]));
if (!is_a_nulls(n))
return n;
}
@@ -75,12 +78,11 @@ 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;
}
@@ -102,6 +104,8 @@ static void *ct_seq_start(struct seq_file *seq, loff_t *pos)
st->time_now = ktime_get_real_ns();
rcu_read_lock();
+
+ nf_conntrack_get_ht(&st->hash, &st->htable_size);
return ct_get_idx(seq, *pos);
}
--
2.5.5
--
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