Messages in this thread Patch in this message | | | From | Siddh Raman Pant <> | 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 |
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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.com Closes: https://syzkaller.appspot.com/bug?extid=bbe84a4010eeea00982d Signed-off-by: Siddh Raman Pant <code@siddh.me> --- 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_llcp_sock *sock, { struct sk_buff *skb; int err, headroom, tailroom; + unsigned long irq_flags; if (sock->ssap == 0) return NULL; + 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 = sock->dev->tx_headroom; tailroom = sock->dev->tx_tailroom; + read_unlock_irqrestore(&sock->rw_dev_lock, irq_flags); + skb = 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; pr_debug("Send UI frame len %zd\n", len); @@ -746,6 +758,18 @@ int nfc_llcp_send_ui_frame(struct nfc_llcp_sock *sock, u8 ssap, u8 dsap, if (local == NULL) return -ENODEV; + read_lock_irqsave(&sock->rw_dev_lock, irq_flags); + + if (!sock->dev) { + read_unlock_irqrestore(&sock->rw_dev_lock, irq_flags); + return -ENODEV; + } + + headroom = sock->dev->tx_headroom; + tailroom = sock->dev->tx_tailroom; + + read_unlock_irqrestore(&sock->rw_dev_lock, irq_flags); + msg_data = kmalloc(len, GFP_USER | __GFP_NOWARN); if (msg_data == NULL) return -ENOMEM; @@ -755,9 +779,6 @@ int nfc_llcp_send_ui_frame(struct nfc_llcp_sock *sock, u8 ssap, u8 dsap, return -EFAULT; } - headroom = sock->dev->tx_headroom; - tailroom = sock->dev->tx_tailroom; - remaining_len = len; msg_ptr = msg_data; 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); +static inline void nfc_llcp_sock_close(struct nfc_llcp_sock *llcp_sock, int err) +{ + struct sock *sk = &llcp_sock->sk; + unsigned long irq_flags; + + if (err) + sk->sk_err = err; + + sk->sk_state = LLCP_CLOSED; + sk->sk_state_change(sk); + + write_lock_irqsave(&llcp_sock->rw_dev_lock, irq_flags); + llcp_sock->dev = 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); 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_local *local, bool device, nfc_llcp_accept_unlink(accept_sk); - if (err) - accept_sk->sk_err = err; - accept_sk->sk_state = LLCP_CLOSED; - accept_sk->sk_state_change(sk); + nfc_llcp_sock_close(lsk, err); bh_unlock_sock(accept_sk); } } - if (err) - sk->sk_err = err; - sk->sk_state = LLCP_CLOSED; - sk->sk_state_change(sk); + nfc_llcp_sock_close(llcp_sock, err); bh_unlock_sock(sk); @@ -130,10 +140,7 @@ static void nfc_llcp_socket_release(struct nfc_llcp_local *local, bool device, nfc_llcp_socket_purge(llcp_sock); - if (err) - sk->sk_err = err; - sk->sk_state = LLCP_CLOSED; - sk->sk_state_change(sk); + nfc_llcp_sock_close(llcp_sock, err); bh_unlock_sock(sk); 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, int type, gfp_t gfp, int k sk->sk_type = type; sk->sk_destruct = llcp_sock_destruct; + rwlock_init(&llcp_sock->rw_dev_lock); + llcp_sock->ssap = 0; llcp_sock->dsap = LLCP_SAP_SDP; llcp_sock->rw = LLCP_MAX_RW + 1; -- 2.42.0
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