From: Liping Zhang <zlpnobody@xxxxxxxxx>
We can still delete the ct helper even if it is in use, this will cause
a use-after-free error. In more detail, I mean:
# nfct helper add ssdp inet udp
# iptables -t raw -A OUTPUT -p udp -j CT --helper ssdp
# nfct helper delete ssdp //--> succeed!
So add reference count to fix this issue, if ct helper is used by
others, reject the delete request.
Apply this patch:
# nfct helper delete ssdp
nfct v1.4.3: netlink error: Device or resource busy
Signed-off-by: Liping Zhang <zlpnobody@xxxxxxxxx>
---
Also note, nft ct helper obj only exists in nf-next tree, so after this
patch appeared in nf-next, I will send another patch to fix it.
include/net/netfilter/nf_conntrack_helper.h | 2 ++
net/netfilter/nf_conntrack_helper.c | 6 ++++++
net/netfilter/nfnetlink_cthelper.c | 17 +++++++++++------
3 files changed, 19 insertions(+), 6 deletions(-)
diff --git a/include/net/netfilter/nf_conntrack_helper.h b/include/net/netfilter/nf_conntrack_helper.h
index 65e1dcf..c7a9ad7 100644
--- a/include/net/netfilter/nf_conntrack_helper.h
+++ b/include/net/netfilter/nf_conntrack_helper.h
@@ -9,6 +9,7 @@
#ifndef _NF_CONNTRACK_HELPER_H
#define _NF_CONNTRACK_HELPER_H
+#include <linux/refcount.h>
#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_extend.h>
#include <net/netfilter/nf_conntrack_expect.h>
@@ -26,6 +27,7 @@ struct nf_conntrack_helper {
struct hlist_node hnode; /* Internal use. */
char name[NF_CT_HELPER_NAME_LEN]; /* name of the module */
+ refcount_t refcnt;
struct module *me; /* pointer to self */
const struct nf_conntrack_expect_policy *expect_policy;
diff --git a/net/netfilter/nf_conntrack_helper.c b/net/netfilter/nf_conntrack_helper.c
index 5275e9a..8fdd03b 100644
--- a/net/netfilter/nf_conntrack_helper.c
+++ b/net/netfilter/nf_conntrack_helper.c
@@ -167,6 +167,10 @@ nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
#endif
if (h != NULL && !try_module_get(h->me))
h = NULL;
+ if (h != NULL && !refcount_inc_not_zero(&h->refcnt)) {
+ module_put(h->me);
+ h = NULL;
+ }
return h;
}
@@ -174,6 +178,7 @@ EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
void nf_conntrack_helper_put(struct nf_conntrack_helper *helper)
{
+ refcount_dec(&helper->refcnt);
module_put(helper->me);
}
EXPORT_SYMBOL_GPL(nf_conntrack_helper_put);
@@ -398,6 +403,7 @@ int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
goto out;
}
}
+ refcount_set(&me->refcnt, 1);
hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
nf_ct_helper_count++;
out:
diff --git a/net/netfilter/nfnetlink_cthelper.c b/net/netfilter/nfnetlink_cthelper.c
index d455581..6e9e3c4 100644
--- a/net/netfilter/nfnetlink_cthelper.c
+++ b/net/netfilter/nfnetlink_cthelper.c
@@ -672,6 +672,7 @@ static int nfnl_cthelper_del(struct net *net, struct sock *nfnl,
tuple_set = true;
}
+ ret = -ENOENT;
list_for_each_entry_safe(nlcth, n, &nfnl_cthelper_list, list) {
cur = &nlcth->helper;
j++;
@@ -685,16 +686,20 @@ static int nfnl_cthelper_del(struct net *net, struct sock *nfnl,
tuple.dst.protonum != cur->tuple.dst.protonum))
continue;
- found = true;
- nf_conntrack_helper_unregister(cur);
- kfree(cur->expect_policy);
+ if (refcount_dec_if_one(&cur->refcnt)) {
+ found = true;
+ nf_conntrack_helper_unregister(cur);
+ kfree(cur->expect_policy);
- list_del(&nlcth->list);
- kfree(nlcth);
+ list_del(&nlcth->list);
+ kfree(nlcth);
+ } else {
+ ret = -EBUSY;
+ }
}
/* Make sure we return success if we flush and there is no helpers */
- return (found || j == 0) ? 0 : -ENOENT;
+ return (found || j == 0) ? 0 : ret;
}
static const struct nla_policy nfnl_cthelper_policy[NFCTH_MAX+1] = {
--
2.5.5
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