Re: [syzbot] [net?] general protection fault in kernel_sock_shutdown (4)

Arjan van de Ven
2026-04-24T18:07:19Z

Unfortunately the AI had a burp and did not write out the proper URL
for analysis data; it should have been

http://oops.fenrus.org/reports/lkml/69ea344f.a00a0220.17a17.0040.GAE_google.com/report.html

and in addition, it made a candidate patch (below)

From: Arjan van de Ven <arjan@linux.intel.com>
Subject: [PATCH] RDMA/rxe: fix double-release race on UDP tunnel socket teardown

This patch is based on a BUG as reported at
https://lore.kernel.org/r/69ea344f.a00a0220.17a17.0040.GAE@google.com.

The Soft RoCE (RXE) driver stores per-network-namespace UDP tunnel
sockets for IPv4 and IPv6 encapsulation. Two independent code paths
tear these sockets down: rxe_ns_exit(), called when a network
namespace is destroyed, and rxe_net_del(), called when an RDMA link
is deleted via netlink. Both paths read the per-namespace socket
pointer and call udp_tunnel_sock_release() on it.

A time-of-check/time-of-use (TOCTOU) race exists in rxe_net_del().
It reads the socket pointer via rxe_ns_pernet_sk4(), then passes it
to rxe_sock_put() for release. If rxe_ns_exit() runs concurrently
between the read and the release, it clears the pointer and calls
udp_tunnel_sock_release() first, causing sock_release() to set
sock->ops = NULL. When rxe_net_del() then calls
udp_tunnel_sock_release() on the same socket, kernel_sock_shutdown()
dereferences the now-NULL sock->ops, triggering a KASAN null-ptr-deref
at offset 0x68 (the shutdown function pointer in struct proto_ops).

A minimal alternative would guard against NULL sock->ops inside
udp_tunnel_sock_release() before calling kernel_sock_shutdown(). That
treats the symptom rather than the root cause and leaves the
double-release of socket state intact.

Add rxe_ns_pernet_take_sk4() and rxe_ns_pernet_take_sk6() which use
xchg() to atomically swap the per-namespace socket pointer to NULL
and return the old value. Replace the non-atomic reads in
rxe_net_del() with these take variants, and release the socket
directly via udp_tunnel_sock_release() without going through
rxe_sock_put().

Whichever teardown path executes take first claims ownership of the
socket; the second caller gets NULL and skips the release, closing
the double-release window.

Link: https://lore.kernel.org/r/69ea344f.a00a0220.17a17.0040.GAE@google.com
Oops-Analysis: http://oops.fenrus.org/reports/lkml/69ea344f.a00a0220.17a17.0040.GAE_google.com/report.html
Fixes: 13f2a53c2a71 ("RDMA/rxe: Add net namespace support for IPv4/IPv6 sockets")
Fixes: f1327abd6abe ("RDMA/rxe: Support RDMA link creation and destruction per net namespace")
Assisted-by: GitHub Copilot patcher:claude linux-kernel-oops-x86.
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: linux-rdma@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: Zhu Yanjun <zyjzyj2000@gmail.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Leon Romanovsky <leon@kernel.org>

---
drivers/infiniband/sw/rxe/rxe_net.c | 8 ++++----
drivers/infiniband/sw/rxe/rxe_ns.c | 14 ++++++++++++++
drivers/infiniband/sw/rxe/rxe_ns.h | 7 +++++++
3 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_net.c b/drivers/infiniband/sw/rxe/rxe_net.c
index 50a2cb5405e22..4f604636cb7b4 100644
--- a/drivers/infiniband/sw/rxe/rxe_net.c
+++ b/drivers/infiniband/sw/rxe/rxe_net.c
@@ -655,13 +655,13 @@ void rxe_net_del(struct ib_device *dev)

net = dev_net(ndev);

- sk = rxe_ns_pernet_sk4(net);
+ sk = rxe_ns_pernet_take_sk4(net);
if (sk)
- rxe_sock_put(sk, rxe_ns_pernet_set_sk4, net);
+ udp_tunnel_sock_release(sk->sk_socket);

- sk = rxe_ns_pernet_sk6(net);
+ sk = rxe_ns_pernet_take_sk6(net);
if (sk)
- rxe_sock_put(sk, rxe_ns_pernet_set_sk6, net);
+ udp_tunnel_sock_release(sk->sk_socket);

dev_put(ndev);
}
diff --git a/drivers/infiniband/sw/rxe/rxe_ns.c b/drivers/infiniband/sw/rxe/rxe_ns.c
index 8b9d734229b24..d9d376e3c670f 100644
--- a/drivers/infiniband/sw/rxe/rxe_ns.c
+++ b/drivers/infiniband/sw/rxe/rxe_ns.c
@@ -91,6 +91,13 @@ void rxe_ns_pernet_set_sk4(struct net *net, struct sock *sk)
synchronize_rcu();
}

+struct sock *rxe_ns_pernet_take_sk4(struct net *net)
+{
+ struct rxe_ns_sock *ns_sk = net_generic(net, rxe_pernet_id);
+
+ return xchg((__force struct sock **)&ns_sk->rxe_sk4, NULL);
+}
+
#if IS_ENABLED(CONFIG_IPV6)
struct sock *rxe_ns_pernet_sk6(struct net *net)
{
@@ -111,6 +118,13 @@ void rxe_ns_pernet_set_sk6(struct net *net, struct sock *sk)
rcu_assign_pointer(ns_sk->rxe_sk6, sk);
synchronize_rcu();
}
+
+struct sock *rxe_ns_pernet_take_sk6(struct net *net)
+{
+ struct rxe_ns_sock *ns_sk = net_generic(net, rxe_pernet_id);
+
+ return xchg((__force struct sock **)&ns_sk->rxe_sk6, NULL);
+}
#endif /* IPV6 */

int rxe_namespace_init(void)
diff --git a/drivers/infiniband/sw/rxe/rxe_ns.h b/drivers/infiniband/sw/rxe/rxe_ns.h
index 4da2709e6b714..9d9a5106b77c8 100644
--- a/drivers/infiniband/sw/rxe/rxe_ns.h
+++ b/drivers/infiniband/sw/rxe/rxe_ns.h
@@ -5,10 +5,17 @@

struct sock *rxe_ns_pernet_sk4(struct net *net);
void rxe_ns_pernet_set_sk4(struct net *net, struct sock *sk);
+struct sock *rxe_ns_pernet_take_sk4(struct net *net);

#if IS_ENABLED(CONFIG_IPV6)
void rxe_ns_pernet_set_sk6(struct net *net, struct sock *sk);
struct sock *rxe_ns_pernet_sk6(struct net *net);
+struct sock *rxe_ns_pernet_take_sk6(struct net *net);
#else /* IPv6 */
static inline struct sock *rxe_ns_pernet_sk6(struct net *net)
{
@@ -18,6 +25,10 @@ static inline void rxe_ns_pernet_set_sk6(struct net *net, struct sock *sk)
{
}

+static inline struct sock *rxe_ns_pernet_take_sk6(struct net *net)
+{
+ return NULL;
+}
#endif /* IPv6 */

int rxe_namespace_init(void);