[PATCH bpf-next v7 1/2] bpf: Allow ksock connect/send calls from wq

[Mahe Tardy <mahe.tardy@gmail.com>]

The initial ksock implementation, commit 7ae4eb14c5f9 ("bpf: Add ksock
kfuncs"), kept LSM checks from the kfunc calls and disallowed
asynchronous workqueues because worker credentials differ from those of
the triggering task. However, discussions at Plumbers 2026[^1] revealed
that bypassing LSM checks for BPF-created sockets could be acceptable.

This patch allows workqueue use while retaining LSM checks for now,
paving the way to call bpf_ksock_connect() and bpf_ksock_send() from
non-sleepable programs, such as tracing programs, in future patches.

Note that bpf_ksock_create() still checks:
* for current to not be a kernel thread (thus excluding bpf workqueue
  callbacks) because the socket is created within a userspace task
  network namespace. It should, most of the time, be the process that
  triggered the SYSCALL program, but could be another task when called
  from bpf_task_work callbacks.
* for current->nsproxy to be non-NULL since when called from a
  bpf_task_work callback and the task is in the do_exit() phase, nsproxy
  is torn down just before the remaining task work is executed.

[^1]: https://lpc.events/event/20/contributions/2430/

Tested-by: Alan Maguire (Oracle) <almagui@kernel.org>
Signed-off-by: Mahe Tardy <mahe.tardy@gmail.com>
---
 net/core/bpf_ksock.c | 24 ++++--------------------
 1 file changed, 4 insertions(+), 20 deletions(-)

diff --git a/net/core/bpf_ksock.c b/net/core/bpf_ksock.c
index e9943aeeadd3..7bf796193ab6 100644
--- a/net/core/bpf_ksock.c
+++ b/net/core/bpf_ksock.c
@@ -37,15 +37,6 @@ static void ksock_release_work_fn(struct work_struct *work)
 	kfree(ks);
 }

-static bool bpf_ksock_has_user_task_context(void)
-{
-	/*
-	 * Task work can run from do_exit() after exit_nsproxy_namespaces()
-	 * cleared current->nsproxy, while current is still not a kthread.
-	 */
-	return !(current->flags & PF_KTHREAD) && current->nsproxy;
-}
-
 __bpf_kfunc_start_defs();

 /**
@@ -59,7 +50,7 @@ __bpf_kfunc_start_defs();
  * This function may sleep (sock_create), so it can only be used
  * in sleepable BPF programs (SYSCALL).
  * It cannot be called from a BPF workqueue callback because that callback
- * does not retain the invoking task's namespace or security context.
+ * does not retain the invoking task's namespace.
  *
  * @opts:	Pointer to struct bpf_ksock_create_opts with socket parameters.
  * @opts__sz:	Size of the opts struct.
@@ -74,11 +65,10 @@ bpf_ksock_create(const struct bpf_ksock_create_opts *opts, u32 opts__sz,
 	int err;

 	/*
-	 * sock_create() derives the network namespace, credentials, and cgroup
-	 * from current. Kernel threads, including BPF workqueue callbacks, do
-	 * not carry the context of the task that invoked the BPF program.
+	 * sock_create() derives the network namespace from current and task
+	 * work can run from do_exit() after exit_nsproxy_namespaces()
 	 */
-	if (!bpf_ksock_has_user_task_context()) {
+	if ((current->flags & PF_KTHREAD) || !current->nsproxy) {
 		err = -EOPNOTSUPP;
 		goto err_out;
 	}
@@ -165,9 +155,6 @@ __bpf_kfunc int bpf_ksock_connect(struct bpf_ksock *ks,
 	struct sockaddr_storage sa;
 	int addrlen;

-	if (!bpf_ksock_has_user_task_context())
-		return -EOPNOTSUPP;
-
 	if (!addr || addr__sz != sizeof(*addr))
 		return -EINVAL;

@@ -247,9 +234,6 @@ __bpf_kfunc int bpf_ksock_send(struct bpf_ksock *ks, const void *data,
 	};
 	int ret;

-	if (!bpf_ksock_has_user_task_context())
-		return -EOPNOTSUPP;
-
 	ret = kernel_sendmsg(ks->sock, &msg, &iov, 1, data__sz);

 	return ret;
--
2.43.0