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    • David S. Miller's avatar
      Merge branch 'nfc-refcounting' · dff90e4a
      David S. Miller authored 
      @ 2023-12-19 17:49 Siddh Raman Pant
  2023-12-19 17:49 ` [PATCH net-next v7 1/2] nfc: llcp_core: Hold a ref to llcp_local->dev when holding a ref to llcp_local Siddh Raman Pant
  2023-12-19 17:49 ` [PATCH net-next v7 2/2] nfc: Do not send datagram if socket state isn't LLCP_BOUND Siddh Raman Pant
  0 siblings, 2 replies; 4+ messages in thread
Siddh Raman Pant says:

====================
[PATCH net-next v7 0/2] nfc: Fix UAF during datagram sending caused by missing refcounting

Changes in v7:
- Stupidly reverted ordering in recv() too, fix that.
- Remove redundant call to nfc_llcp_sock_free().

Changes in v6:
- Revert label introduction from v4, and thus also v5 entirely.

Changes in v5:
- Move reason = LLCP_DM_REJ under the fail_put_sock label.
- Checkpatch now warns about == NULL check for new_sk, so fix that,
  and also at other similar places in the same function.

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.

---

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.
====================
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      dff90e4a
    • Siddh Raman Pant's avatar
      nfc: Do not send datagram if socket state isn't LLCP_BOUND · 6ec0d752
      Siddh Raman Pant authored 
      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: default avatarSiddh Raman Pant <code@siddh.me>
Reviewed-by: default avatarKrzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: default avatarSuman Ghosh <sumang@marvell.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      6ec0d752
    • Siddh Raman Pant's avatar
      nfc: llcp_core: Hold a ref to llcp_local->dev when holding a ref to llcp_local · c95f9195
      Siddh Raman Pant authored 
      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: c7aa1225 ("NFC: Take a reference on the LLCP local pointer when creating a socket")
Reviewed-by: default avatarSuman Ghosh <sumang@marvell.com>
Signed-off-by: default avatarSiddh Raman Pant <code@siddh.me>
Reviewed-by: default avatarKrzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      c95f9195
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