[PATCH 4.20 148/171] netfilter: nft_compat: dont use refcount_inc on newly allocated entry

Greg Kroah-Hartman
2019-03-12T17:52:21Z

[ Upstream commit 947e492c0fc2132ae5fca081a9c2952ccaab0404 ]

When I moved the refcount to refcount_t type I missed the fact that
refcount_inc() will result in use-after-free warning with
CONFIG_REFCOUNT_FULL=y builds.

The correct fix would be to init the reference count to 1 at allocation
time, but, unfortunately we cannot do this, as we can't undo that
in case something else fails later in the batch.

So only solution I see is to special-case the 'new entry' condition
and replace refcount_inc() with a "delayed" refcount_set(1) in this case,
as done here.

The .activate callback can be removed to simplify things, we only
need to make sure that deactivate() decrements/unlinks the entry
from the list at end of transaction phase (commit or abort).

Fixes: 12c44aba6618 ("netfilter: nft_compat: use refcnt_t type for nft_xt reference count")
Reported-by: Jordan Glover <Golden_Miller83@protonmail.ch>
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 | 62 ++++++++++++++------------------------
1 file changed, 23 insertions(+), 39 deletions(-)

diff --git a/net/netfilter/nft_compat.c b/net/netfilter/nft_compat.c
index 5fd94f7fdb94..0a4bad55a8aa 100644
--- a/net/netfilter/nft_compat.c
+++ b/net/netfilter/nft_compat.c
@@ -61,6 +61,21 @@ static struct nft_compat_net *nft_compat_pernet(struct net *net)
return net_generic(net, nft_compat_net_id);
}

+static void nft_xt_get(struct nft_xt *xt)
+{
+ /* refcount_inc() warns on 0 -> 1 transition, but we can't
+ * init the reference count to 1 in .select_ops -- we can't
+ * undo such an increase when another expression inside the same
+ * rule fails afterwards.
+ */
+ if (xt->listcnt == 0)
+ refcount_set(&xt->refcnt, 1);
+ else
+ refcount_inc(&xt->refcnt);
+
+ xt->listcnt++;
+}
+
static bool nft_xt_put(struct nft_xt *xt)
{
if (refcount_dec_and_test(&xt->refcnt)) {
@@ -291,7 +306,7 @@ nft_target_init(const struct nft_ctx *ctx, const struct nft_expr *expr,
return -EINVAL;

nft_xt = container_of(expr->ops, struct nft_xt, ops);
- refcount_inc(&nft_xt->refcnt);
+ nft_xt_get(nft_xt);
return 0;
}

@@ -505,7 +520,7 @@ __nft_match_init(const struct nft_ctx *ctx, const struct nft_expr *expr,
return ret;

nft_xt = container_of(expr->ops, struct nft_xt, ops);
- refcount_inc(&nft_xt->refcnt);
+ nft_xt_get(nft_xt);
return 0;
}

@@ -559,45 +574,16 @@ 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,
enum nft_trans_phase phase)
{
struct nft_xt *xt = container_of(expr->ops, struct nft_xt, ops);

- if (phase == NFT_TRANS_COMMIT)
- return;
-
- if (--xt->listcnt == 0)
- list_del_init(&xt->head);
+ if (phase == NFT_TRANS_ABORT || phase == NFT_TRANS_COMMIT) {
+ if (--xt->listcnt == 0)
+ list_del_init(&xt->head);
+ }
}

static void
@@ -853,7 +839,6 @@ 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;
@@ -871,7 +856,7 @@ nft_match_select_ops(const struct nft_ctx *ctx,

nft_match->ops.size = matchsize;

- nft_match->listcnt = 1;
+ nft_match->listcnt = 0;
list_add(&nft_match->head, &cn->nft_match_list);

return &nft_match->ops;
@@ -958,7 +943,6 @@ 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;
@@ -969,7 +953,7 @@ nft_target_select_ops(const struct nft_ctx *ctx,
else
nft_target->ops.eval = nft_target_eval_xt;

- nft_target->listcnt = 1;
+ nft_target->listcnt = 0;
list_add(&nft_target->head, &cn->nft_target_list);

return &nft_target->ops;
--
2.19.1