Re: [PATCH v2 1/1] RDMA/rxe: Fix Use-After-Free problem in rxe_net_del

[Zhu Yanjun <yanjun.zhu@linux.dev>]

gently ping

在 2026/5/18 19:35, Zhu Yanjun 写道:
> syzbot reported a general protection fault (KASAN: null-ptr-deref) in
> kernel_sock_shutdown() called during the software RoCE (rxe) link
> deletion path (rxe_dellink -> rxe_net_del).
> 
> The call trace is as below:
> "
> rdma_rxe: rxe_newlink: failed to add lo
> Oops: gen[  127.022080][ T5982] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000004: 0000 [#1] SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027]
> CPU: 1 UID: 0 PID: 5982 Comm: syz.3.20 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
> ...
> Call Trace:
>   <TASK>
>   udp_tunnel_sock_release+0x6d/0x80 net/ipv4/udp_tunnel_core.c:197
>   rxe_release_udp_tunnel drivers/infiniband/sw/rxe/rxe_net.c:294 [inline]
>   rxe_sock_put drivers/infiniband/sw/rxe/rxe_net.c:639 [inline]
>   rxe_net_del+0xfb/0x290 drivers/infiniband/sw/rxe/rxe_net.c:660
>   rxe_dellink+0x15/0x20 drivers/infiniband/sw/rxe/rxe.c:254
>   nldev_dellink+0x304/0x3d0 drivers/infiniband/core/nldev.c:1849
>   rdma_nl_rcv_msg drivers/infiniband/core/netlink.c:-1 [inline]
>   rdma_nl_rcv_skb drivers/infiniband/core/netlink.c:239 [inline]
>   rdma_nl_rcv+0x6d7/0xa10 drivers/infiniband/core/netlink.c:259
>   netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
>   netlink_unicast+0x780/0x920 net/netlink/af_netlink.c:1345
>   netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1895
>   sock_sendmsg_nosec+0x112/0x150 net/socket.c:797
>   __sock_sendmsg net/socket.c:812 [inline]
>   ____sys_sendmsg+0x55c/0x870 net/socket.c:2716
>   ___sys_sendmsg+0x2a5/0x360 net/socket.c:2770
>   __sys_sendmsg net/socket.c:2802 [inline]
>   __do_sys_sendmsg net/socket.c:2807 [inline]
>   __se_sys_sendmsg net/socket.c:2805 [inline]
>   __x64_sys_sendmsg+0x1c3/0x2a0 net/socket.c:2805
>   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>   do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f89172fcdd9
> RSP: 002b:00007ffe8bf8c018 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 00007f8917575fa0 RCX: 00007f89172fcdd9
> RDX: 0000000000000000 RSI: 00002000000002c0 RDI: 0000000000000006
> RBP: 00007f8917392d69 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f8917575fac R14: 00007f8917575fa0 R15: 00007f8917575fa0
>   </TASK>
> "
> 
> The root cause is a TOCTOU (Time-of-Check to Time-of-Use) race condition
> in rxe_net_del(). Previously, the function fetched the socket pointer
> via rxe_ns_pernet_sk4/6() outside the critical section, and then
> acquired the lock to release it via rxe_sock_put().
> 
> In a highly concurrent teardown environment, another thread could close
> and clear the pernet socket after it was fetched but before the lock
> was acquired. This causes rxe_sock_put() to operate on a dangling or
> already cleared socket pointer, leading to a NULL pointer dereference
> when kernel_sock_shutdown() attempts to access sock->sk.
> 
> Fix this by introducing a dedicated, per-netns mutex 'release_lock'
> and extending its scope. The socket pointers are now fetched, checked,
> and released entirely within the same locked critical section. This
> ensures the atomicity of the socket lookup and teardown sequence.
> 
> Since new mutex lock is introduced, remove the unnecessary rcu locks.
> 
> Reported-by: syzbot+d8f76778263ab65c2b21@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=d8f76778263ab65c2b21
> Fixes: f1327abd6abe ("RDMA/rxe: Support RDMA link creation and destruction per net namespace")
> Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
> ---
> V1 -> V2: Remove the unnecessary rcu locks, following Leon's advice.
> ---
>   drivers/infiniband/sw/rxe/rxe_net.c | 49 +++++++++++++++++++-----
>   drivers/infiniband/sw/rxe/rxe_ns.c  | 58 ++++++++++++++++-------------
>   drivers/infiniband/sw/rxe/rxe_ns.h  |  3 ++
>   3 files changed, 74 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/infiniband/sw/rxe/rxe_net.c b/drivers/infiniband/sw/rxe/rxe_net.c
> index 50a2cb5405e2..0bf5b0eabc7b 100644
> --- a/drivers/infiniband/sw/rxe/rxe_net.c
> +++ b/drivers/infiniband/sw/rxe/rxe_net.c
> @@ -135,13 +135,21 @@ static struct dst_entry *rxe_find_route6(struct rxe_qp *qp,
>   {
>   	struct dst_entry *ndst;
>   	struct flowi6 fl6 = {};
> +	struct sock *sk;
>   
>   	fl6.flowi6_oif = ndev->ifindex;
>   	memcpy(&fl6.saddr, saddr, sizeof(*saddr));
>   	memcpy(&fl6.daddr, daddr, sizeof(*daddr));
>   	fl6.flowi6_proto = IPPROTO_UDP;
>   
> -	ndst = ip6_dst_lookup_flow(net, rxe_ns_pernet_sk6(net), &fl6, NULL);
> +	rxe_ns_lock(net);
> +	sk = rxe_ns_pernet_sk6(net);
> +	if (sk)
> +		sock_hold(sk);
> +	rxe_ns_unlock(net);
> +
> +	ndst = ip6_dst_lookup_flow(net, sk, &fl6, NULL);
> +	sock_put(sk);
>   	if (IS_ERR(ndst)) {
>   		rxe_dbg_qp(qp, "no route to %pI6\n", daddr);
>   		return NULL;
> @@ -655,6 +663,8 @@ void rxe_net_del(struct ib_device *dev)
>   
>   	net = dev_net(ndev);
>   
> +	rxe_ns_lock(net);
> +
>   	sk = rxe_ns_pernet_sk4(net);
>   	if (sk)
>   		rxe_sock_put(sk, rxe_ns_pernet_set_sk4, net);
> @@ -663,6 +673,8 @@ void rxe_net_del(struct ib_device *dev)
>   	if (sk)
>   		rxe_sock_put(sk, rxe_ns_pernet_set_sk6, net);
>   
> +	rxe_ns_unlock(net);
> +
>   	dev_put(ndev);
>   }
>   
> @@ -754,52 +766,67 @@ static struct notifier_block rxe_net_notifier = {
>   
>   static int rxe_net_ipv4_init(struct net *net)
>   {
> -	struct sock *sk;
>   	struct socket *sock;
> +	struct sock *sk;
> +	int ret = 0;
>   
> +	rxe_ns_lock(net);
>   	sk = rxe_ns_pernet_sk4(net);
>   	if (sk) {
>   		sock_hold(sk);
> -		return 0;
> +		ret = 0;
> +		goto out_unlock;
>   	}
>   
>   	sock = rxe_setup_udp_tunnel(net, htons(ROCE_V2_UDP_DPORT), false);
>   	if (IS_ERR(sock)) {
>   		pr_err("Failed to create IPv4 UDP tunnel\n");
> -		return -1;
> +		ret = -1;
> +		goto out_unlock;
>   	}
> +
>   	rxe_ns_pernet_set_sk4(net, sock->sk);
>   
> -	return 0;
> +out_unlock:
> +	rxe_ns_unlock(net);
> +	return ret;
>   }
>   
>   static int rxe_net_ipv6_init(struct net *net)
>   {
> +	int ret = 0;
>   #if IS_ENABLED(CONFIG_IPV6)
> -	struct sock *sk;
>   	struct socket *sock;
> +	struct sock *sk;
>   
> +	rxe_ns_lock(net);
>   	sk = rxe_ns_pernet_sk6(net);
>   	if (sk) {
>   		sock_hold(sk);
> -		return 0;
> +		ret = 0;
> +		goto out_unlock;
>   	}
>   
>   	sock = rxe_setup_udp_tunnel(net, htons(ROCE_V2_UDP_DPORT), true);
>   	if (PTR_ERR(sock) == -EAFNOSUPPORT) {
>   		pr_warn("IPv6 is not supported, can not create a UDPv6 socket\n");
> -		return 0;
> +		ret = 0;
> +		goto out_unlock;
>   	}
>   
>   	if (IS_ERR(sock)) {
>   		pr_err("Failed to create IPv6 UDP tunnel\n");
> -		return -1;
> +		ret = -1;
> +		goto out_unlock;
>   	}
>   
>   	rxe_ns_pernet_set_sk6(net, sock->sk);
>   
> +out_unlock:
> +	rxe_ns_unlock(net);
> +
>   #endif
> -	return 0;
> +	return ret;
>   }
>   
>   int rxe_register_notifier(void)
> @@ -840,9 +867,11 @@ int rxe_net_init(struct net_device *ndev)
>   
>   err_out:
>   	/* If ipv6 error, release ipv4 resource */
> +	rxe_ns_lock(net);
>   	sk = rxe_ns_pernet_sk4(net);
>   	if (sk)
>   		rxe_sock_put(sk, rxe_ns_pernet_set_sk4, net);
> +	rxe_ns_unlock(net);
>   
>   	return err;
>   }
> diff --git a/drivers/infiniband/sw/rxe/rxe_ns.c b/drivers/infiniband/sw/rxe/rxe_ns.c
> index 8b9d734229b2..744a3d16f963 100644
> --- a/drivers/infiniband/sw/rxe/rxe_ns.c
> +++ b/drivers/infiniband/sw/rxe/rxe_ns.c
> @@ -14,8 +14,9 @@
>    * Per network namespace data
>    */
>   struct rxe_ns_sock {
> -	struct sock __rcu *rxe_sk4;
> -	struct sock __rcu *rxe_sk6;
> +	struct sock	*rxe_sk4;
> +	struct sock	*rxe_sk6;
> +	struct mutex	ns_mutex_lock;
>   };
>   
>   /*
> @@ -31,10 +32,26 @@ static int rxe_ns_init(struct net *net)
>   	/* defer socket create in the namespace to the first
>   	 * device create.
>   	 */
> +	struct rxe_ns_sock *ns_sk = net_generic(net, rxe_pernet_id);
>   
> +	mutex_init(&ns_sk->ns_mutex_lock);
>   	return 0;
>   }
>   
> +void rxe_ns_lock(struct net *net)
> +{
> +	struct rxe_ns_sock *ns_sk = net_generic(net, rxe_pernet_id);
> +
> +	mutex_lock(&ns_sk->ns_mutex_lock);
> +}
> +
> +void rxe_ns_unlock(struct net *net)
> +{
> +	struct rxe_ns_sock *ns_sk = net_generic(net, rxe_pernet_id);
> +
> +	mutex_unlock(&ns_sk->ns_mutex_lock);
> +}
> +
>   static void rxe_ns_exit(struct net *net)
>   {
>   	/* called when the network namespace is removed
> @@ -42,23 +59,24 @@ static void rxe_ns_exit(struct net *net)
>   	struct rxe_ns_sock *ns_sk = net_generic(net, rxe_pernet_id);
>   	struct sock *sk;
>   
> -	rcu_read_lock();
> -	sk = rcu_dereference(ns_sk->rxe_sk4);
> -	rcu_read_unlock();
> +	rxe_ns_lock(net);
> +	sk = ns_sk->rxe_sk4;
>   	if (sk) {
> -		rcu_assign_pointer(ns_sk->rxe_sk4, NULL);
> +		ns_sk->rxe_sk4 = NULL;
>   		udp_tunnel_sock_release(sk->sk_socket);
>   	}
>   
>   #if IS_ENABLED(CONFIG_IPV6)
> -	rcu_read_lock();
> -	sk = rcu_dereference(ns_sk->rxe_sk6);
> -	rcu_read_unlock();
> +	sk = ns_sk->rxe_sk6;
>   	if (sk) {
> -		rcu_assign_pointer(ns_sk->rxe_sk6, NULL);
> +		ns_sk->rxe_sk6 = NULL;
>   		udp_tunnel_sock_release(sk->sk_socket);
>   	}
>   #endif
> +
> +	rxe_ns_unlock(net);
> +
> +	mutex_destroy(&ns_sk->ns_mutex_lock);
>   }
>   
>   /*
> @@ -74,42 +92,30 @@ static struct pernet_operations rxe_net_ops = {
>   struct sock *rxe_ns_pernet_sk4(struct net *net)
>   {
>   	struct rxe_ns_sock *ns_sk = net_generic(net, rxe_pernet_id);
> -	struct sock *sk;
> -
> -	rcu_read_lock();
> -	sk = rcu_dereference(ns_sk->rxe_sk4);
> -	rcu_read_unlock();
>   
> -	return sk;
> +	return ns_sk->rxe_sk4;
>   }
>   
>   void rxe_ns_pernet_set_sk4(struct net *net, struct sock *sk)
>   {
>   	struct rxe_ns_sock *ns_sk = net_generic(net, rxe_pernet_id);
>   
> -	rcu_assign_pointer(ns_sk->rxe_sk4, sk);
> -	synchronize_rcu();
> +	ns_sk->rxe_sk4 = sk;
>   }
>   
>   #if IS_ENABLED(CONFIG_IPV6)
>   struct sock *rxe_ns_pernet_sk6(struct net *net)
>   {
>   	struct rxe_ns_sock *ns_sk = net_generic(net, rxe_pernet_id);
> -	struct sock *sk;
> -
> -	rcu_read_lock();
> -	sk = rcu_dereference(ns_sk->rxe_sk6);
> -	rcu_read_unlock();
>   
> -	return sk;
> +	return ns_sk->rxe_sk6;
>   }
>   
>   void rxe_ns_pernet_set_sk6(struct net *net, struct sock *sk)
>   {
>   	struct rxe_ns_sock *ns_sk = net_generic(net, rxe_pernet_id);
>   
> -	rcu_assign_pointer(ns_sk->rxe_sk6, sk);
> -	synchronize_rcu();
> +	ns_sk->rxe_sk6 = sk;
>   }
>   #endif /* IPV6 */
>   
> diff --git a/drivers/infiniband/sw/rxe/rxe_ns.h b/drivers/infiniband/sw/rxe/rxe_ns.h
> index 4da2709e6b71..e6cc6b5a4806 100644
> --- a/drivers/infiniband/sw/rxe/rxe_ns.h
> +++ b/drivers/infiniband/sw/rxe/rxe_ns.h
> @@ -20,6 +20,9 @@ static inline void rxe_ns_pernet_set_sk6(struct net *net, struct sock *sk)
>   }
>   #endif /* IPv6 */
>   
> +void rxe_ns_lock(struct net *net);
> +void rxe_ns_unlock(struct net *net);
> +
>   int rxe_namespace_init(void);
>   void rxe_namespace_exit(void);
>