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(110.226.61.26 [110.226.61.26]) by mx.zoho.in with SMTPS id 1700943995162403.864052366456; Sun, 26 Nov 2023 01:56:35 +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, syzbot+bbe84a4010eeea00982d@syzkaller.appspotmail.com Subject: [PATCH 2/4] nfc: Protect access to nfc_dev in an llcp_sock with a rwlock Date: Sun, 26 Nov 2023 01:56:17 +0530 Message-ID: <7c198c2aa08b34045b8f9e0afe3d0b3bf5802180.1700943019.git.code@siddh.me> X-Mailer: git-send-email 2.42.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ZohoMailClient: External Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" llcp_sock_sendmsg() calls nfc_llcp_send_ui_frame(), which accesses the nfc_dev from the llcp_sock for getting the headroom and tailroom needed for skb allocation. Parallely, the nfc_dev can be freed via the nfc_unregister_device() codepath (nfc_release() being called due to the class unregister in nfc_exit()), leading to the UAF reported by Syzkaller. We have the following call tree before freeing: nfc_unregister_device() -> nfc_llcp_unregister_device() -> local_cleanup() -> nfc_llcp_socket_release() nfc_llcp_socket_release() sets the state of sockets to LLCP_CLOSED, and this is encountered necessarily before any freeing of nfc_dev. Thus, add a rwlock in struct llcp_sock to synchronize access to nfc_dev. nfc_dev in an llcp_sock will be NULLed in a write critical section when socket state has been set to closed. Thus, we can avoid the UAF by bailing out from a read critical section upon seeing NULL. Since this is repeated multiple times in nfc_llcp_socket_release(), extract the behaviour into a new function. Reported-and-tested-by: syzbot+bbe84a4010eeea00982d@syzkaller.appspotmail.c= om Closes: https://syzkaller.appspot.com/bug?extid=3Dbbe84a4010eeea00982d Signed-off-by: Siddh Raman Pant --- net/nfc/llcp.h | 1 + net/nfc/llcp_commands.c | 27 ++++++++++++++++++++++++--- net/nfc/llcp_core.c | 31 +++++++++++++++++++------------ net/nfc/llcp_sock.c | 2 ++ 4 files changed, 46 insertions(+), 15 deletions(-) diff --git a/net/nfc/llcp.h b/net/nfc/llcp.h index d8345ed57c95..800cbe8e3d6b 100644 --- a/net/nfc/llcp.h +++ b/net/nfc/llcp.h @@ -102,6 +102,7 @@ struct nfc_llcp_local { struct nfc_llcp_sock { struct sock sk; struct nfc_dev *dev; + rwlock_t rw_dev_lock; struct nfc_llcp_local *local; u32 target_idx; u32 nfc_protocol; diff --git a/net/nfc/llcp_commands.c b/net/nfc/llcp_commands.c index 39c7c59bbf66..b132830bc206 100644 --- a/net/nfc/llcp_commands.c +++ b/net/nfc/llcp_commands.c @@ -315,13 +315,24 @@ static struct sk_buff *llcp_allocate_pdu(struct nfc_l= lcp_sock *sock, { struct sk_buff *skb; int err, headroom, tailroom; + unsigned long irq_flags; =20 if (sock->ssap =3D=3D 0) return NULL; =20 + read_lock_irqsave(&sock->rw_dev_lock, irq_flags); + + if (!sock->dev) { + read_unlock_irqrestore(&sock->rw_dev_lock, irq_flags); + pr_err("NFC device does not exit\n"); + return NULL; + } + headroom =3D sock->dev->tx_headroom; tailroom =3D sock->dev->tx_tailroom; =20 + read_unlock_irqrestore(&sock->rw_dev_lock, irq_flags); + skb =3D nfc_alloc_send_skb(&sock->sk, MSG_DONTWAIT, size + LLCP_HEADER_SIZE, headroom, tailroom, &err); @@ -739,6 +750,7 @@ int nfc_llcp_send_ui_frame(struct nfc_llcp_sock *sock, = u8 ssap, u8 dsap, u8 *msg_ptr, *msg_data; u16 remote_miu; int err, headroom, tailroom; + unsigned long irq_flags; =20 pr_debug("Send UI frame len %zd\n", len); =20 @@ -746,6 +758,18 @@ int nfc_llcp_send_ui_frame(struct nfc_llcp_sock *sock,= u8 ssap, u8 dsap, if (local =3D=3D NULL) return -ENODEV; =20 + read_lock_irqsave(&sock->rw_dev_lock, irq_flags); + + if (!sock->dev) { + read_unlock_irqrestore(&sock->rw_dev_lock, irq_flags); + return -ENODEV; + } + + headroom =3D sock->dev->tx_headroom; + tailroom =3D sock->dev->tx_tailroom; + + read_unlock_irqrestore(&sock->rw_dev_lock, irq_flags); + msg_data =3D kmalloc(len, GFP_USER | __GFP_NOWARN); if (msg_data =3D=3D NULL) return -ENOMEM; @@ -755,9 +779,6 @@ int nfc_llcp_send_ui_frame(struct nfc_llcp_sock *sock, = u8 ssap, u8 dsap, return -EFAULT; } =20 - headroom =3D sock->dev->tx_headroom; - tailroom =3D sock->dev->tx_tailroom; - remaining_len =3D len; msg_ptr =3D msg_data; =20 diff --git a/net/nfc/llcp_core.c b/net/nfc/llcp_core.c index 1dac28136e6a..a565712d7db8 100644 --- a/net/nfc/llcp_core.c +++ b/net/nfc/llcp_core.c @@ -20,6 +20,22 @@ static LIST_HEAD(llcp_devices); /* Protects llcp_devices list */ static DEFINE_SPINLOCK(llcp_devices_lock); =20 +static inline void nfc_llcp_sock_close(struct nfc_llcp_sock *llcp_sock, in= t err) +{ + struct sock *sk =3D &llcp_sock->sk; + unsigned long irq_flags; + + if (err) + sk->sk_err =3D err; + + sk->sk_state =3D LLCP_CLOSED; + sk->sk_state_change(sk); + + write_lock_irqsave(&llcp_sock->rw_dev_lock, irq_flags); + llcp_sock->dev =3D NULL; + write_unlock_irqrestore(&llcp_sock->rw_dev_lock, irq_flags); +} + static void nfc_llcp_rx_skb(struct nfc_llcp_local *local, struct sk_buff *= skb); =20 void nfc_llcp_sock_link(struct llcp_sock_list *l, struct sock *sk) @@ -96,19 +112,13 @@ static void nfc_llcp_socket_release(struct nfc_llcp_lo= cal *local, bool device, =20 nfc_llcp_accept_unlink(accept_sk); =20 - if (err) - accept_sk->sk_err =3D err; - accept_sk->sk_state =3D LLCP_CLOSED; - accept_sk->sk_state_change(sk); + nfc_llcp_sock_close(lsk, err); =20 bh_unlock_sock(accept_sk); } } =20 - if (err) - sk->sk_err =3D err; - sk->sk_state =3D LLCP_CLOSED; - sk->sk_state_change(sk); + nfc_llcp_sock_close(llcp_sock, err); =20 bh_unlock_sock(sk); =20 @@ -130,10 +140,7 @@ static void nfc_llcp_socket_release(struct nfc_llcp_lo= cal *local, bool device, =20 nfc_llcp_socket_purge(llcp_sock); =20 - if (err) - sk->sk_err =3D err; - sk->sk_state =3D LLCP_CLOSED; - sk->sk_state_change(sk); + nfc_llcp_sock_close(llcp_sock, err); =20 bh_unlock_sock(sk); =20 diff --git a/net/nfc/llcp_sock.c b/net/nfc/llcp_sock.c index 645677f84dba..ef1ab88a5e4f 100644 --- a/net/nfc/llcp_sock.c +++ b/net/nfc/llcp_sock.c @@ -983,6 +983,8 @@ struct sock *nfc_llcp_sock_alloc(struct socket *sock, i= nt type, gfp_t gfp, int k sk->sk_type =3D type; sk->sk_destruct =3D llcp_sock_destruct; =20 + rwlock_init(&llcp_sock->rw_dev_lock); + llcp_sock->ssap =3D 0; llcp_sock->dsap =3D LLCP_SAP_SDP; llcp_sock->rw =3D LLCP_MAX_RW + 1; --=20 2.42.0