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(122.170.35.155 [122.170.35.155]) by mx.zoho.in with SMTPS id 1701531671764225.8381284275174; Sat, 2 Dec 2023 21:11:11 +0530 (IST) From: Siddh Raman Pant To: Krzysztof Kozlowski , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Samuel Ortiz , syzbot+bbe84a4010eeea00982d@syzkaller.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 Date: Sat, 2 Dec 2023 21:10:58 +0530 Message-ID: <476cccdcb57645784889fc82f0c7c10ff4c8b8c0.1701530776.git.code@siddh.me> X-Mailer: git-send-email 2.42.0 In-Reply-To: References: MIME-Version: 1.0 X-ZohoMailClient: External X-Spam-Status: No, score=-0.9 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on agentk.vger.email Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (agentk.vger.email [0.0.0.0]); Sat, 02 Dec 2023 07:42:07 -0800 (PST) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1784185335467140822 X-GMAIL-MSGID: 1784185335467140822 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: c7aa12252f51 ("NFC: Take a reference on the LLCP local pointer when creating a socket") Signed-off-by: Siddh Raman Pant --- 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);