[PATCH 4.20 005/171] netfilter: nft_compat: make lists per netns

Greg Kroah-Hartman
2019-03-12T18:11:02Z

[ Upstream commit cf52572ebbd7189a1966c2b5fc34b97078cd1dce ]

There are two problems with nft_compat since the netlink config
plane uses a per-netns mutex:

1. Concurrent add/del accesses to the same list
2. accesses to a list element after it has been free'd already.

This patch fixes the first problem.

Freeing occurs from a work queue, after transaction mutexes have been
released, i.e., it still possible for a new transaction (even from
same net ns) to find the to-be-deleted expression in the list.

The ->destroy functions are not allowed to have any such side effects,
i.e. the list_del() in the destroy function is not allowed.

This part of the problem is solved in the next patch.
I tried to make this work by serializing list access via mutex
and by moving list_del() to a deactivate callback, but
Taehee spotted following race on this approach:

NET #0 NET #1
>select_ops()
->init()
->select_ops()
->deactivate()
->destroy()
nft_xt_put()
kfree_rcu(xt, rcu_head);
->init() <-- use-after-free occurred.

Unfortunately, we can't increment reference count in
select_ops(), because we can't undo the refcount increase in
case a different expression fails in the same batch.

(The destroy hook will only be called in case the expression
was initialized successfully).

Fixes: f102d66b335a ("netfilter: nf_tables: use dedicated mutex to guard transactions")
Reported-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/nft_compat.c | 129 +++++++++++++++++++++++++------------
1 file changed, 89 insertions(+), 40 deletions(-)

diff --git a/net/netfilter/nft_compat.c b/net/netfilter/nft_compat.c
index 791f3e693e3d..d3412138e000 100644
--- a/net/netfilter/nft_compat.c
+++ b/net/netfilter/nft_compat.c
@@ -22,6 +22,7 @@
#include <linux/netfilter_bridge/ebtables.h>
#include <linux/netfilter_arp/arp_tables.h>
#include <net/netfilter/nf_tables.h>
+#include <net/netns/generic.h>

struct nft_xt {
struct list_head head;
@@ -43,6 +44,20 @@ struct nft_xt_match_priv {
void *info;
};

+struct nft_compat_net {
+ struct list_head nft_target_list;
+ struct list_head nft_match_list;
+};
+
+static unsigned int nft_compat_net_id __read_mostly;
+static struct nft_expr_type nft_match_type;
+static struct nft_expr_type nft_target_type;
+
+static struct nft_compat_net *nft_compat_pernet(struct net *net)
+{
+ return net_generic(net, nft_compat_net_id);
+}
+
static bool nft_xt_put(struct nft_xt *xt)
{
if (refcount_dec_and_test(&xt->refcnt)) {
@@ -735,10 +750,6 @@ static const struct nfnetlink_subsystem nfnl_compat_subsys = {
.cb = nfnl_nft_compat_cb,
};

-static LIST_HEAD(nft_match_list);
-
-static struct nft_expr_type nft_match_type;
-
static bool nft_match_cmp(const struct xt_match *match,
const char *name, u32 rev, u32 family)
{
@@ -750,6 +761,7 @@ static const struct nft_expr_ops *
nft_match_select_ops(const struct nft_ctx *ctx,
const struct nlattr * const tb[])
{
+ struct nft_compat_net *cn;
struct nft_xt *nft_match;
struct xt_match *match;
unsigned int matchsize;
@@ -766,8 +778,10 @@ nft_match_select_ops(const struct nft_ctx *ctx,
rev = ntohl(nla_get_be32(tb[NFTA_MATCH_REV]));
family = ctx->family;

+ cn = nft_compat_pernet(ctx->net);
+
/* Re-use the existing match if it's already loaded. */
- list_for_each_entry(nft_match, &nft_match_list, head) {
+ list_for_each_entry(nft_match, &cn->nft_match_list, head) {
struct xt_match *match = nft_match->ops.data;

if (nft_match_cmp(match, mt_name, rev, family))
@@ -811,7 +825,7 @@ nft_match_select_ops(const struct nft_ctx *ctx,

nft_match->ops.size = matchsize;

- list_add(&nft_match->head, &nft_match_list);
+ list_add(&nft_match->head, &cn->nft_match_list);

return &nft_match->ops;
err:
@@ -827,10 +841,6 @@ static struct nft_expr_type nft_match_type __read_mostly = {
.owner = THIS_MODULE,
};

-static LIST_HEAD(nft_target_list);
-
-static struct nft_expr_type nft_target_type;
-
static bool nft_target_cmp(const struct xt_target *tg,
const char *name, u32 rev, u32 family)
{
@@ -842,6 +852,7 @@ static const struct nft_expr_ops *
nft_target_select_ops(const struct nft_ctx *ctx,
const struct nlattr * const tb[])
{
+ struct nft_compat_net *cn;
struct nft_xt *nft_target;
struct xt_target *target;
char *tg_name;
@@ -862,8 +873,9 @@ nft_target_select_ops(const struct nft_ctx *ctx,
strcmp(tg_name, "standard") == 0)
return ERR_PTR(-EINVAL);

+ cn = nft_compat_pernet(ctx->net);
/* Re-use the existing target if it's already loaded. */
- list_for_each_entry(nft_target, &nft_target_list, head) {
+ list_for_each_entry(nft_target, &cn->nft_target_list, head) {
struct xt_target *target = nft_target->ops.data;

if (!target->target)
@@ -908,7 +920,7 @@ nft_target_select_ops(const struct nft_ctx *ctx,
else
nft_target->ops.eval = nft_target_eval_xt;

- list_add(&nft_target->head, &nft_target_list);
+ list_add(&nft_target->head, &cn->nft_target_list);

return &nft_target->ops;
err:
@@ -924,13 +936,74 @@ static struct nft_expr_type nft_target_type __read_mostly = {
.owner = THIS_MODULE,
};

+static int __net_init nft_compat_init_net(struct net *net)
+{
+ struct nft_compat_net *cn = nft_compat_pernet(net);
+
+ INIT_LIST_HEAD(&cn->nft_target_list);
+ INIT_LIST_HEAD(&cn->nft_match_list);
+
+ return 0;
+}
+
+static void __net_exit nft_compat_exit_net(struct net *net)
+{
+ struct nft_compat_net *cn = nft_compat_pernet(net);
+ struct nft_xt *xt, *next;
+
+ if (list_empty(&cn->nft_match_list) &&
+ list_empty(&cn->nft_target_list))
+ return;
+
+ /* If there was an error that caused nft_xt expr to not be initialized
+ * fully and noone else requested the same expression later, the lists
+ * contain 0-refcount entries that still hold module reference.
+ *
+ * Clean them here.
+ */
+ mutex_lock(&net->nft.commit_mutex);
+ list_for_each_entry_safe(xt, next, &cn->nft_target_list, head) {
+ struct xt_target *target = xt->ops.data;
+
+ list_del_init(&xt->head);
+
+ if (refcount_read(&xt->refcnt))
+ continue;
+ module_put(target->me);
+ kfree(xt);
+ }
+
+ list_for_each_entry_safe(xt, next, &cn->nft_match_list, head) {
+ struct xt_match *match = xt->ops.data;
+
+ list_del_init(&xt->head);
+
+ if (refcount_read(&xt->refcnt))
+ continue;
+ module_put(match->me);
+ kfree(xt);
+ }
+ mutex_unlock(&net->nft.commit_mutex);
+}
+
+static struct pernet_operations nft_compat_net_ops = {
+ .init = nft_compat_init_net,
+ .exit = nft_compat_exit_net,
+ .id = &nft_compat_net_id,
+ .size = sizeof(struct nft_compat_net),
+};
+
static int __init nft_compat_module_init(void)
{
int ret;

+ ret = register_pernet_subsys(&nft_compat_net_ops);
+ if (ret < 0)
+ goto err_target;
+
ret = nft_register_expr(&nft_match_type);
if (ret < 0)
- return ret;
+ goto err_pernet;

ret = nft_register_expr(&nft_target_type);
if (ret < 0)
@@ -943,45 +1016,21 @@ static int __init nft_compat_module_init(void)
}

return ret;
-
err_target:
nft_unregister_expr(&nft_target_type);
err_match:
nft_unregister_expr(&nft_match_type);
+err_pernet:
+ unregister_pernet_subsys(&nft_compat_net_ops);
return ret;
}

static void __exit nft_compat_module_exit(void)
{
- struct nft_xt *xt, *next;
-
- /* list should be empty here, it can be non-empty only in case there
- * was an error that caused nft_xt expr to not be initialized fully
- * and noone else requested the same expression later.
- *
- * In this case, the lists contain 0-refcount entries that still
- * hold module reference.
- */
- list_for_each_entry_safe(xt, next, &nft_target_list, head) {
- struct xt_target *target = xt->ops.data;
-
- if (WARN_ON_ONCE(refcount_read(&xt->refcnt)))
- continue;
- module_put(target->me);
- kfree(xt);
- }
-
- list_for_each_entry_safe(xt, next, &nft_match_list, head) {
- struct xt_match *match = xt->ops.data;
-
- if (WARN_ON_ONCE(refcount_read(&xt->refcnt)))
- continue;
- module_put(match->me);
- kfree(xt);
- }
nfnetlink_subsys_unregister(&nfnl_compat_subsys);
nft_unregister_expr(&nft_target_type);
nft_unregister_expr(&nft_match_type);
+ unregister_pernet_subsys(&nft_compat_net_ops);
}

MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_NFT_COMPAT);
--
2.19.1