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nfc: llcp_core: Hold a ref to llcp_local->dev when holding a ref to llcp_local

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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@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=bbe84a4010eeea00982d
Fixes: c7aa12252f ("NFC: Take a reference on the LLCP local pointer when creating a socket")
Reviewed-by: Suman Ghosh <sumang@marvell.com>
Signed-off-by: Siddh Raman Pant <code@siddh.me>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Siddh Raman Pant 2023-12-19 23:19:43 +05:30 committed by David S. Miller
parent 7c5e046bdc
commit c95f919567
1 changed files with 36 additions and 3 deletions
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39
net/nfc/llcp_core.c
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@ -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 +974,17 @@ 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;
sock_put(&new_sock->sk);
release_sock(&sock->sk);
sock_put(&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 +1621,16 @@ 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);