(Very sorry for the delay in sending this.)
For connectionless transmission, llcp_sock_sendmsg() codepath will
eventually call nfc_alloc_send_skb() which takes in an nfc_dev as
an argument for calculating the total size for skb allocation.
virtual_ncidev_close() codepath eventually releases socket by calling
nfc_llcp_socket_release() (which sets the sk->sk_state to LLCP_CLOSED)
and afterwards the nfc_dev will be eventually freed.
When an ndev gets freed, llcp_sock_sendmsg() will result in an
use-after-free as it
(1) doesn't have any checks in place for avoiding the datagram sending.
(2) calls nfc_llcp_send_ui_frame(), which also has a do-while loop
which can race with freeing. This loop contains the call to
nfc_alloc_send_skb() where we dereference the nfc_dev pointer.
nfc_dev is being freed because we do not hold a reference to it when
we hold a reference to llcp_local. Thus, virtual_ncidev_close()
eventually calls nfc_release() due to refcount going to 0.
Since state has to be LLCP_BOUND for datagram sending, we can bail out
early in llcp_sock_sendmsg().
Please review and let me know if any errors are there, and hopefully
this gets accepted.
Thanks,
Siddh
Changes in v4:
- Fix put ordering and comments.
- Separate freeing in recv() into end labels.
- Remove obvious comment and add reasoning.
- Picked up r-bs by Suman.
Changes in v3:
- Fix missing freeing statements.
Changes in v2:
- Add net-next in patch subject.
- Removed unnecessary extra lock and hold nfc_dev ref when holding llcp_sock.
- Remove last formatting patch.
- Picked up r-b from Krzysztof for LLCP_BOUND patch.
Siddh Raman Pant (2):
nfc: llcp_core: Hold a ref to llcp_local->dev when holding a ref to
llcp_local
nfc: Do not send datagram if socket state isn't LLCP_BOUND
net/nfc/llcp_core.c | 55 ++++++++++++++++++++++++++++++++++-----------
net/nfc/llcp_sock.c | 5 +++++
2 files changed, 47 insertions(+), 13 deletions(-)
--
2.42.0
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: [email protected]
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 <[email protected]>
Reviewed-by: Suman Ghosh <[email protected]>
---
net/nfc/llcp_core.c | 55 ++++++++++++++++++++++++++++++++++-----------
1 file changed, 42 insertions(+), 13 deletions(-)
diff --git a/net/nfc/llcp_core.c b/net/nfc/llcp_core.c
index 1dac28136e6a..0ae89ab42aaa 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,
@@ -930,9 +945,7 @@ static void nfc_llcp_recv_connect(struct nfc_llcp_local *local,
if (sk_acceptq_is_full(parent)) {
reason = LLCP_DM_REJ;
- release_sock(&sock->sk);
- sock_put(&sock->sk);
- goto fail;
+ goto fail_put_sock;
}
if (sock->ssap == LLCP_SDP_UNBOUND) {
@@ -942,9 +955,7 @@ static void nfc_llcp_recv_connect(struct nfc_llcp_local *local,
if (ssap == LLCP_SAP_MAX) {
reason = LLCP_DM_REJ;
- release_sock(&sock->sk);
- sock_put(&sock->sk);
- goto fail;
+ goto fail_put_sock;
}
sock->ssap = ssap;
@@ -953,14 +964,18 @@ static void nfc_llcp_recv_connect(struct nfc_llcp_local *local,
new_sk = nfc_llcp_sock_alloc(NULL, parent->sk_type, GFP_ATOMIC, 0);
if (new_sk == NULL) {
reason = LLCP_DM_REJ;
- release_sock(&sock->sk);
- sock_put(&sock->sk);
- goto fail;
+ goto fail_put_sock;
}
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;
+ goto fail_free_new_sock;
+ }
+
+ new_sock->dev = local->dev;
new_sock->rw = sock->rw;
new_sock->miux = sock->miux;
new_sock->nfc_protocol = sock->nfc_protocol;
@@ -1004,8 +1019,13 @@ static void nfc_llcp_recv_connect(struct nfc_llcp_local *local,
return;
+fail_free_new_sock:
+ sock_put(&new_sock->sk);
+ nfc_llcp_sock_free(new_sock);
+fail_put_sock:
+ release_sock(&sock->sk);
+ sock_put(&sock->sk);
fail:
- /* Send DM */
nfc_llcp_send_dm(local, dsap, ssap, reason);
}
@@ -1597,7 +1617,16 @@ 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
As we know we cannot send the datagram (state can be set to LLCP_CLOSED
by nfc_llcp_socket_release()), there is no need to proceed further.
Thus, bail out early from llcp_sock_sendmsg().
Signed-off-by: Siddh Raman Pant <[email protected]>
Reviewed-by: Krzysztof Kozlowski <[email protected]>
Reviewed-by: Suman Ghosh <[email protected]>
---
net/nfc/llcp_sock.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/net/nfc/llcp_sock.c b/net/nfc/llcp_sock.c
index 645677f84dba..819157bbb5a2 100644
--- a/net/nfc/llcp_sock.c
+++ b/net/nfc/llcp_sock.c
@@ -796,6 +796,11 @@ static int llcp_sock_sendmsg(struct socket *sock, struct msghdr *msg,
}
if (sk->sk_type == SOCK_DGRAM) {
+ if (sk->sk_state != LLCP_BOUND) {
+ release_sock(sk);
+ return -ENOTCONN;
+ }
+
DECLARE_SOCKADDR(struct sockaddr_nfc_llcp *, addr,
msg->msg_name);
--
2.42.0
On Sat, 2023-12-09 at 16:34 +0530, Siddh Raman Pant wrote:
> 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: [email protected]
> 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 <[email protected]>
> Reviewed-by: Suman Ghosh <[email protected]>
> ---
> net/nfc/llcp_core.c | 55 ++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 42 insertions(+), 13 deletions(-)
>
> diff --git a/net/nfc/llcp_core.c b/net/nfc/llcp_core.c
> index 1dac28136e6a..0ae89ab42aaa 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,
> @@ -930,9 +945,7 @@ static void nfc_llcp_recv_connect(struct nfc_llcp_local *local,
>
> if (sk_acceptq_is_full(parent)) {
> reason = LLCP_DM_REJ;
'reason' is set to 'LLCP_DM_REJ' every time you jump to the
'fail_put_sock' or 'fail_free_new_sock' labels, you can as well move
the assignment after 'fail_put_sock:'
Cheers,
Paolo
On Tue, 12 Dec 2023 18:31:57 +0530, Paolo Abeni wrote:
> On Sat, 2023-12-09 at 16:34 +0530, Siddh Raman Pant wrote:
> > static struct nfc_llcp_sock *nfc_llcp_sock_get(struct nfc_llcp_local *local,
> > @@ -930,9 +945,7 @@ static void nfc_llcp_recv_connect(struct nfc_llcp_local *local,
> >
> > if (sk_acceptq_is_full(parent)) {
> > reason = LLCP_DM_REJ;
>
> 'reason' is set to 'LLCP_DM_REJ' every time you jump to the
> 'fail_put_sock' or 'fail_free_new_sock' labels, you can as well move
> the assignment after 'fail_put_sock:'
Sure, I'll send a patch with that.
Thanks,
Siddh