[PATCH 4.20 006/171] netfilter: nft_compat: destroy function must not have side effects

Greg Kroah-Hartman
2019-03-12T17:12:01Z

[ Upstream commit b2e3d68d1251a051a620f9086e18f7ffa6833b5b ]

The nft_compat destroy function deletes the nft_xt object from a list.
This isn't allowed anymore. Destroy functions are called asynchronously,
i.e. next batch can find the object that has a pending ->destroy()
invocation:

cpu0 cpu1
worker
->destroy for_each_entry()
if (x == ...
return x->ops;
list_del(x)
kfree_rcu(x)
expr->ops->... // ops was free'd

To resolve this, the list_del needs to occur before the transaction
mutex gets released. nf_tables has a 'deactivate' hook for this
purpose, so use that to unlink the object from the list.

Fixes: 0935d5588400 ("netfilter: nf_tables: asynchronous release")
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 | 48 +++++++++++++++++++++++++++++++++++++-
1 file changed, 47 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nft_compat.c b/net/netfilter/nft_compat.c
index d3412138e000..a354e9771697 100644
--- a/net/netfilter/nft_compat.c
+++ b/net/netfilter/nft_compat.c
@@ -29,6 +29,9 @@ struct nft_xt {
struct nft_expr_ops ops;
refcount_t refcnt;

+ /* used only when transaction mutex is locked */
+ unsigned int listcnt;
+
/* Unlike other expressions, ops doesn't have static storage duration.
* nft core assumes they do. We use kfree_rcu so that nft core can
* can check expr->ops->size even after nft_compat->destroy() frees
@@ -61,7 +64,7 @@ static struct nft_compat_net *nft_compat_pernet(struct net *net)
static bool nft_xt_put(struct nft_xt *xt)
{
if (refcount_dec_and_test(&xt->refcnt)) {
- list_del(&xt->head);
+ WARN_ON_ONCE(!list_empty(&xt->head));
kfree_rcu(xt, rcu_head);
return true;
}
@@ -556,6 +559,43 @@ nft_match_destroy(const struct nft_ctx *ctx, const struct nft_expr *expr)
__nft_match_destroy(ctx, expr, nft_expr_priv(expr));
}

+static void nft_compat_activate(const struct nft_ctx *ctx,
+ const struct nft_expr *expr,
+ struct list_head *h)
+{
+ struct nft_xt *xt = container_of(expr->ops, struct nft_xt, ops);
+
+ if (xt->listcnt == 0)
+ list_add(&xt->head, h);
+
+ xt->listcnt++;
+}
+
+static void nft_compat_activate_mt(const struct nft_ctx *ctx,
+ const struct nft_expr *expr)
+{
+ struct nft_compat_net *cn = nft_compat_pernet(ctx->net);
+
+ nft_compat_activate(ctx, expr, &cn->nft_match_list);
+}
+
+static void nft_compat_activate_tg(const struct nft_ctx *ctx,
+ const struct nft_expr *expr)
+{
+ struct nft_compat_net *cn = nft_compat_pernet(ctx->net);
+
+ nft_compat_activate(ctx, expr, &cn->nft_target_list);
+}
+
+static void nft_compat_deactivate(const struct nft_ctx *ctx,
+ const struct nft_expr *expr)
+{
+ struct nft_xt *xt = container_of(expr->ops, struct nft_xt, ops);
+
+ if (--xt->listcnt == 0)
+ list_del_init(&xt->head);
+}
+
static void
nft_match_large_destroy(const struct nft_ctx *ctx, const struct nft_expr *expr)
{
@@ -809,6 +849,8 @@ nft_match_select_ops(const struct nft_ctx *ctx,
nft_match->ops.eval = nft_match_eval;
nft_match->ops.init = nft_match_init;
nft_match->ops.destroy = nft_match_destroy;
+ nft_match->ops.activate = nft_compat_activate_mt;
+ nft_match->ops.deactivate = nft_compat_deactivate;
nft_match->ops.dump = nft_match_dump;
nft_match->ops.validate = nft_match_validate;
nft_match->ops.data = match;
@@ -825,6 +867,7 @@ nft_match_select_ops(const struct nft_ctx *ctx,

nft_match->ops.size = matchsize;

+ nft_match->listcnt = 1;
list_add(&nft_match->head, &cn->nft_match_list);

return &nft_match->ops;
@@ -911,6 +954,8 @@ nft_target_select_ops(const struct nft_ctx *ctx,
nft_target->ops.size = NFT_EXPR_SIZE(XT_ALIGN(target->targetsize));
nft_target->ops.init = nft_target_init;
nft_target->ops.destroy = nft_target_destroy;
+ nft_target->ops.activate = nft_compat_activate_tg;
+ nft_target->ops.deactivate = nft_compat_deactivate;
nft_target->ops.dump = nft_target_dump;
nft_target->ops.validate = nft_target_validate;
nft_target->ops.data = target;
@@ -920,6 +965,7 @@ nft_target_select_ops(const struct nft_ctx *ctx,
else
nft_target->ops.eval = nft_target_eval_xt;

+ nft_target->listcnt = 1;
list_add(&nft_target->head, &cn->nft_target_list);

return &nft_target->ops;
--
2.19.1