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netfilter: nft_compat: make lists per netns 

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: f102d66b33 ("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>
This commit is contained in:
Florian Westphal 2019-01-14 14:28:49 +01:00 committed by Pablo Neira Ayuso
parent 12c44aba66
commit cf52572ebb
1 changed files with 89 additions and 40 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

129
net/netfilter/nft_compat.c
View File

@ -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)) {
@ -734,10 +749,6 @@ 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)
{
@ -749,6 +760,7 @@ 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;
@ -765,8 +777,10 @@ 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))
@ -810,7 +824,7 @@ 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:
@ -826,10 +840,6 @@ 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)
{
@ -841,6 +851,7 @@ 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;
@ -861,8 +872,9 @@ 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)
@ -907,7 +919,7 @@ 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:
@ -923,13 +935,74 @@ 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)
@ -942,45 +1015,21 @@ 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);