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Message-ID: <476cccdcb57645784889fc82f0c7c10ff4c8b8c0.1701530776.git.code@siddh.me>
Date: Sat, 2 Dec 2023 21:10:58 +0530
From: Siddh Raman Pant <code@...dh.me>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
Samuel Ortiz <sameo@...ux.intel.com>,
syzbot+bbe84a4010eeea00982d@...kaller.appspotmail.com
Subject: [PATCH net-next v2 1/2] nfc: llcp_core: Hold a ref to llcp_local->dev when holding a ref to llcp_local
llcp_sock_sendmsg() calls nfc_llcp_send_ui_frame() which in turn calls
nfc_alloc_send_skb(), which accesses the nfc_dev from the llcp_sock for
getting the headroom and tailroom needed for skb allocation.
Parallelly the nfc_dev can be freed, as the refcount is decreased via
nfc_free_device(), leading to a UAF reported by Syzkaller, which can
be summarized as follows:
(1) llcp_sock_sendmsg() -> nfc_llcp_send_ui_frame()
-> nfc_alloc_send_skb() -> Dereference *nfc_dev
(2) virtual_ncidev_close() -> nci_free_device() -> nfc_free_device()
-> put_device() -> nfc_release() -> Free *nfc_dev
When a reference to llcp_local is acquired, we do not acquire the same
for the nfc_dev. This leads to freeing even when the llcp_local is in
use, and this is the case with the UAF described above too.
Thus, when we acquire a reference to llcp_local, we should acquire a
reference to nfc_dev, and release the references appropriately later.
References for llcp_local is initialized in nfc_llcp_register_device()
(which is called by nfc_register_device()). Thus, we should acquire a
reference to nfc_dev there.
nfc_unregister_device() calls nfc_llcp_unregister_device() which in
turn calls nfc_llcp_local_put(). Thus, the reference to nfc_dev is
appropriately released later.
Reported-and-tested-by: syzbot+bbe84a4010eeea00982d@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=bbe84a4010eeea00982d
Fixes: c7aa12252f51 ("NFC: Take a reference on the LLCP local pointer when creating a socket")
Signed-off-by: Siddh Raman Pant <code@...dh.me>
---
net/nfc/llcp_core.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
diff --git a/net/nfc/llcp_core.c b/net/nfc/llcp_core.c
index 1dac28136e6a..a574c653e5d2 100644
--- a/net/nfc/llcp_core.c
+++ b/net/nfc/llcp_core.c
@@ -145,6 +145,9 @@ 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)
{
+ if (!nfc_get_device(local->dev->idx))
+ return NULL;
+
kref_get(&local->ref);
return local;
@@ -180,6 +183,7 @@ int nfc_llcp_local_put(struct nfc_llcp_local *local)
if (local == NULL)
return 0;
+ nfc_put_device(local->dev);
return kref_put(&local->ref, local_release);
}
@@ -959,8 +963,17 @@ 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);
+ 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 +1610,11 @@ int nfc_llcp_register_device(struct nfc_dev *ndev)
if (local == NULL)
return -ENOMEM;
- local->dev = ndev;
+ /* Hold a reference to the device. */
+ local->dev = nfc_get_device(ndev->idx);
+ if (!local->dev)
+ return -ENODEV;
+
INIT_LIST_HEAD(&local->list);
kref_init(&local->ref);
mutex_init(&local->sdp_lock);
--
2.42.0
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