[PATCH -stable,4.19.x 09/40] netfilter: nf_tables: don't skip expired elements during walk

Pablo Neira Ayuso
2024-06-13T01:02:24Z

commit 24138933b97b055d486e8064b4a1721702442a9b upstream.

There is an asymmetry between commit/abort and preparation phase if the
following conditions are met:

1. set is a verdict map ("1.2.3.4 : jump foo")
2. timeouts are enabled

In this case, following sequence is problematic:

1. element E in set S refers to chain C
2. userspace requests removal of set S
3. kernel does a set walk to decrement chain->use count for all elements
from preparation phase
4. kernel does another set walk to remove elements from the commit phase
(or another walk to do a chain->use increment for all elements from
abort phase)

If E has already expired in 1), it will be ignored during list walk, so its use count
won't have been changed.

Then, when set is culled, ->destroy callback will zap the element via
nf_tables_set_elem_destroy(), but this function is only safe for
elements that have been deactivated earlier from the preparation phase:
lack of earlier deactivate removes the element but leaks the chain use
count, which results in a WARN splat when the chain gets removed later,
plus a leak of the nft_chain structure.

Update pipapo_get() not to skip expired elements, otherwise flush
command reports bogus ENOENT errors.

Fixes: 3c4287f62044 ("nf_tables: Add set type for arbitrary concatenation of ranges")
Fixes: 8d8540c4f5e0 ("netfilter: nft_set_rbtree: add timeout support")
Fixes: 9d0982927e79 ("netfilter: nft_hash: add support for timeouts")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
net/netfilter/nf_tables_api.c | 4 ++++
net/netfilter/nft_set_hash.c | 2 --
net/netfilter/nft_set_rbtree.c | 2 --
3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index a9dfe3183565..a0cc186cc17d 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -4159,8 +4159,12 @@ static int nf_tables_dump_setelem(const struct nft_ctx *ctx,
const struct nft_set_iter *iter,
struct nft_set_elem *elem)
{
+ const struct nft_set_ext *ext = nft_set_elem_ext(set, elem->priv);
struct nft_set_dump_args *args;

+ if (nft_set_elem_expired(ext))
+ return 0;
+
args = container_of(iter, struct nft_set_dump_args, iter);
return nf_tables_fill_setelem(args->skb, set, elem);
}
diff --git a/net/netfilter/nft_set_hash.c b/net/netfilter/nft_set_hash.c
index f2be05731740..c899df945b0d 100644
--- a/net/netfilter/nft_set_hash.c
+++ b/net/netfilter/nft_set_hash.c
@@ -268,8 +268,6 @@ static void nft_rhash_walk(const struct nft_ctx *ctx, struct nft_set *set,

if (iter->count < iter->skip)
goto cont;
- if (nft_set_elem_expired(&he->ext))
- goto cont;
if (!nft_set_elem_active(&he->ext, iter->genmask))
goto cont;

diff --git a/net/netfilter/nft_set_rbtree.c b/net/netfilter/nft_set_rbtree.c
index daf5df18c580..fc069ffc38f7 100644
--- a/net/netfilter/nft_set_rbtree.c
+++ b/net/netfilter/nft_set_rbtree.c
@@ -556,8 +556,6 @@ static void nft_rbtree_walk(const struct nft_ctx *ctx,

if (iter->count < iter->skip)
goto cont;
- if (nft_set_elem_expired(&rbe->ext))
- goto cont;
if (!nft_set_elem_active(&rbe->ext, iter->genmask))
goto cont;

--
2.30.2