[PATCH 4.9 04/49] af_key: relax availability checks for skb size calculation

Greg Kroah-Hartman
2021-02-22T13:39:24Z

From: Cong Wang <cong.wang@bytedance.com>

[ Upstream commit afbc293add6466f8f3f0c3d944d85f53709c170f ]

xfrm_probe_algs() probes kernel crypto modules and changes the
availability of struct xfrm_algo_desc. But there is a small window
where ealg->available and aalg->available get changed between
count_ah_combs()/count_esp_combs() and dump_ah_combs()/dump_esp_combs(),
in this case we may allocate a smaller skb but later put a larger
amount of data and trigger the panic in skb_put().

Fix this by relaxing the checks when counting the size, that is,
skipping the test of ->available. We may waste some memory for a few
of sizeof(struct sadb_comb), but it is still much better than a panic.

Reported-by: syzbot+b2bf2652983d23734c5c@syzkaller.appspotmail.com
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/key/af_key.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/key/af_key.c b/net/key/af_key.c
index 76a008b1cbe5f..adc93329e6aac 100644
--- a/net/key/af_key.c
+++ b/net/key/af_key.c
@@ -2933,7 +2933,7 @@ static int count_ah_combs(const struct xfrm_tmpl *t)
break;
if (!aalg->pfkey_supported)
continue;
- if (aalg_tmpl_set(t, aalg) && aalg->available)
+ if (aalg_tmpl_set(t, aalg))
sz += sizeof(struct sadb_comb);
}
return sz + sizeof(struct sadb_prop);
@@ -2951,7 +2951,7 @@ static int count_esp_combs(const struct xfrm_tmpl *t)
if (!ealg->pfkey_supported)
continue;

- if (!(ealg_tmpl_set(t, ealg) && ealg->available))
+ if (!(ealg_tmpl_set(t, ealg)))
continue;

for (k = 1; ; k++) {
@@ -2962,7 +2962,7 @@ static int count_esp_combs(const struct xfrm_tmpl *t)
if (!aalg->pfkey_supported)
continue;

- if (aalg_tmpl_set(t, aalg) && aalg->available)
+ if (aalg_tmpl_set(t, aalg))
sz += sizeof(struct sadb_comb);
}
}
--
2.27.0