Re: [syzbot] [net?] [nfc?] KASAN: slab-use-after-free Read in nfc_alloc_send_skb

From: Siddh Raman Pant
Date: Sat Dec 09 2023 - 04:27:27 EST


#syz test https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git main

---
net/nfc/llcp_core.c | 40 +++++++++++++++++++++++++++++++++++++---
1 file changed, 37 insertions(+), 3 deletions(-)

diff --git a/net/nfc/llcp_core.c b/net/nfc/llcp_core.c
index 1dac28136e6a..fadc8a9ec4df 100644
--- a/net/nfc/llcp_core.c
+++ b/net/nfc/llcp_core.c
@@ -145,6 +145,13 @@ static void nfc_llcp_socket_release(struct nfc_llcp_local *local, bool device,

static struct nfc_llcp_local *nfc_llcp_local_get(struct nfc_llcp_local *local)
{
+ /* Since using nfc_llcp_local may result in usage of nfc_dev, whenever
+ * we hold a reference to local, we also need to hold a reference to
+ * the device to avoid UAF.
+ */
+ if (!nfc_get_device(local->dev->idx))
+ return NULL;
+
kref_get(&local->ref);

return local;
@@ -177,10 +184,18 @@ static void local_release(struct kref *ref)

int nfc_llcp_local_put(struct nfc_llcp_local *local)
{
+ struct nfc_dev *dev;
+ int ret;
+
if (local == NULL)
return 0;

- return kref_put(&local->ref, local_release);
+ dev = local->dev;
+
+ ret = kref_put(&local->ref, local_release);
+ nfc_put_device(dev);
+
+ return ret;
}

static struct nfc_llcp_sock *nfc_llcp_sock_get(struct nfc_llcp_local *local,
@@ -959,8 +974,18 @@ static void nfc_llcp_recv_connect(struct nfc_llcp_local *local,
}

new_sock = nfc_llcp_sock(new_sk);
- new_sock->dev = local->dev;
+
new_sock->local = nfc_llcp_local_get(local);
+ if (!new_sock->local) {
+ reason = LLCP_DM_REJ;
+ release_sock(&sock->sk);
+ sock_put(&sock->sk);
+ sock_put(&new_sock->sk);
+ nfc_llcp_sock_free(new_sock);
+ goto fail;
+ }
+
+ new_sock->dev = local->dev;
new_sock->rw = sock->rw;
new_sock->miux = sock->miux;
new_sock->nfc_protocol = sock->nfc_protocol;
@@ -1597,7 +1622,16 @@ int nfc_llcp_register_device(struct nfc_dev *ndev)
if (local == NULL)
return -ENOMEM;

- local->dev = ndev;
+ /* As we are going to initialize local's refcount, we need to get the
+ * nfc_dev to avoid UAF, otherwise there is no point in continuing.
+ * See nfc_llcp_local_get().
+ */
+ local->dev = nfc_get_device(ndev->idx);
+ if (!local->dev) {
+ kfree(local);
+ return -ENODEV;
+ }
+
INIT_LIST_HEAD(&local->list);
kref_init(&local->ref);
mutex_init(&local->sdp_lock);
--
2.42.0