x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 864 insertions, 0 deletions

diff --git a/fs/smb/server/connection.c b/fs/smb/server/connection.c
new file mode 100644
index 000000000..4cb92d659
--- /dev/null
+++ b/fs/smb/server/connection.c
@@ -0,0 +1,864 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *   Copyright (C) 2016 Namjae Jeon <namjae.jeon@protocolfreedom.org>
+ *   Copyright (C) 2018 Samsung Electronics Co., Ltd.
+ */
+
+#include <linux/mutex.h>
+#include <linux/freezer.h>
+#include <linux/module.h>
+
+#include "server.h"
+#include "smb_common.h"
+#include "mgmt/ksmbd_ida.h"
+#include "mgmt/user_session.h"
+#include "connection.h"
+#include "vfs_cache.h"
+#include "compress.h"
+#include "transport_tcp.h"
+#include "transport_rdma.h"
+#include "misc.h"
+
+static DEFINE_MUTEX(init_lock);
+
+static struct ksmbd_conn_ops default_conn_ops;
+
+DEFINE_HASHTABLE(conn_list, CONN_HASH_BITS);
+DECLARE_RWSEM(conn_list_lock);
+
+#ifdef CONFIG_PROC_FS
+static struct proc_dir_entry *proc_clients;
+
+static const char *ksmbd_conn_state_string(struct ksmbd_conn *conn)
+{
+	switch (READ_ONCE(conn->status)) {
+	case KSMBD_SESS_NEW:
+		return "new";
+	case KSMBD_SESS_GOOD:
+		return "good";
+	case KSMBD_SESS_EXITING:
+		return "exiting";
+	case KSMBD_SESS_NEED_RECONNECT:
+		return "reconnect";
+	case KSMBD_SESS_NEED_NEGOTIATE:
+		return "negotiate";
+	case KSMBD_SESS_NEED_SETUP:
+		return "setup";
+	case KSMBD_SESS_RELEASING:
+		return "releasing";
+	default:
+		return "unknown";
+	}
+}
+
+static const char *ksmbd_conn_transport_string(struct ksmbd_conn *conn)
+{
+	if (conn->transport->ops->rdma_read || conn->transport->ops->rdma_write)
+		return "smbdirect";
+	return "tcp";
+}
+
+static void proc_show_conn_feature(struct seq_file *m, bool *separator,
+				   bool enabled, const char *name)
+{
+	if (!enabled)
+		return;
+	seq_printf(m, "%s%s", *separator ? "," : "", name);
+	*separator = true;
+}
+
+static void proc_show_conn_features(struct seq_file *m,
+				    struct ksmbd_conn *conn)
+{
+	bool separator = false;
+
+	proc_show_conn_feature(m, &separator,
+			       conn->sign || conn->signing_negotiated, "sign");
+	proc_show_conn_feature(m, &separator, conn->cipher_type, "encrypt");
+	proc_show_conn_feature(m, &separator,
+			       conn->compress_algorithm != SMB3_COMPRESS_NONE,
+			       "compress");
+	proc_show_conn_feature(m, &separator, conn->rdma_transform_ids,
+			       "rdma-transform");
+	proc_show_conn_feature(m, &separator, conn->posix_ext_supported, "posix");
+	if (!separator)
+		seq_puts(m, "none");
+}
+
+static int proc_show_clients(struct seq_file *m, void *v)
+{
+	struct ksmbd_conn *conn;
+	struct timespec64 now, t;
+	int i;
+
+	down_read(&conn_list_lock);
+	hash_for_each(conn_list, i, conn, hlist) {
+		unsigned int outstanding_credits, total_credits;
+		unsigned long id;
+		void *entry;
+		unsigned int sessions = 0;
+
+		jiffies_to_timespec64(jiffies - conn->last_active, &t);
+		ktime_get_real_ts64(&now);
+		t = timespec64_sub(now, t);
+
+		spin_lock(&conn->credits_lock);
+		outstanding_credits = conn->outstanding_credits;
+		total_credits = conn->total_credits;
+		spin_unlock(&conn->credits_lock);
+
+		rcu_read_lock();
+		xa_for_each(&conn->sessions, id, entry)
+			sessions++;
+		rcu_read_unlock();
+#if IS_ENABLED(CONFIG_IPV6)
+		if (!conn->inet_addr)
+			seq_printf(m, "client:\t%pI6c\n", &conn->inet6_addr);
+		else
+#endif
+			seq_printf(m, "client:\t%pI4\n", &conn->inet_addr);
+		seq_printf(m, "transport:\t%s\n", ksmbd_conn_transport_string(conn));
+		seq_printf(m, "state:\t%s\n", ksmbd_conn_state_string(conn));
+		seq_printf(m, "dialect:\t0x%04x\n", conn->dialect);
+		seq_printf(m, "credits:\t%u/%u\n", outstanding_credits,
+			   total_credits);
+		seq_printf(m, "sessions:\t%u\n", sessions);
+		seq_printf(m, "open_files:\t%d\n",
+			   atomic_read(&conn->stats.open_files_count));
+		seq_printf(m, "requests:\t%lld\n",
+			   atomic64_read(&conn->stats.request_served));
+		seq_puts(m, "features:\t");
+		proc_show_conn_features(m, conn);
+		seq_printf(m, "\nlast_active:\t%ptT\n\n", &t);
+	}
+	up_read(&conn_list_lock);
+	return 0;
+}
+
+static int create_proc_clients(void)
+{
+	proc_clients = ksmbd_proc_create("clients",
+					 proc_show_clients, NULL);
+	if (!proc_clients)
+		return -ENOMEM;
+	return 0;
+}
+
+static void delete_proc_clients(void)
+{
+	if (proc_clients) {
+		proc_remove(proc_clients);
+		proc_clients = NULL;
+	}
+}
+#else
+static int create_proc_clients(void) { return 0; }
+static void delete_proc_clients(void) {}
+#endif
+
+static struct workqueue_struct *ksmbd_conn_wq;
+
+int ksmbd_conn_wq_init(void)
+{
+	ksmbd_conn_wq = alloc_workqueue("ksmbd-conn-release",
+					WQ_UNBOUND | WQ_MEM_RECLAIM, 0);
+	if (!ksmbd_conn_wq)
+		return -ENOMEM;
+	return 0;
+}
+
+void ksmbd_conn_wq_destroy(void)
+{
+	if (ksmbd_conn_wq) {
+		destroy_workqueue(ksmbd_conn_wq);
+		ksmbd_conn_wq = NULL;
+	}
+}
+
+/*
+ * __ksmbd_conn_release_work() - perform the final, once-per-struct cleanup
+ * of a ksmbd_conn whose refcount has just dropped to zero.
+ *
+ * This is the common release path used by ksmbd_conn_put() for the embedded
+ * state that outlives the connection thread: async_ida and the attached
+ * transport (which owns the socket and iov for TCP).  Called from a workqueue
+ * so that sleep-allowed teardown (sock_release -> tcp_close ->
+ * lock_sock_nested) never runs from an RCU softirq callback (free_opinfo_rcu)
+ * or any other non-sleeping putter context.
+ */
+static void __ksmbd_conn_release_work(struct work_struct *work)
+{
+	struct ksmbd_conn *conn =
+		container_of(work, struct ksmbd_conn, release_work);
+
+	ida_destroy(&conn->async_ida);
+	conn->transport->ops->free_transport(conn->transport);
+	kfree_sensitive(conn);
+}
+
+/**
+ * ksmbd_conn_get() - take a reference on @conn and return it.
+ *
+ * @conn: connection instance to get a reference to
+ *
+ * Returns @conn unchanged so callers can write
+ * "fp->conn = ksmbd_conn_get(work->conn);" in one expression.  Returns NULL
+ * if @conn is NULL.
+ */
+struct ksmbd_conn *ksmbd_conn_get(struct ksmbd_conn *conn)
+{
+	if (!conn)
+		return NULL;
+
+	atomic_inc(&conn->refcnt);
+	return conn;
+}
+
+/**
+ * ksmbd_conn_put() - drop a reference and, if it was the last, queue the
+ * release onto ksmbd_conn_wq so it runs from process context.
+ *
+ * @conn: connection instance to put a reference to
+ *
+ * Callable from any context including RCU softirq callbacks and non-sleeping
+ * locks; the actual release is deferred to the workqueue.  ksmbd_conn_wq is
+ * created in ksmbd_server_init() before any conn can be allocated and is
+ * destroyed in ksmbd_server_exit() after rcu_barrier(), so it is always
+ * non-NULL while a conn reference is held.
+ */
+void ksmbd_conn_put(struct ksmbd_conn *conn)
+{
+	if (!conn)
+		return;
+
+	if (atomic_dec_and_test(&conn->refcnt))
+		queue_work(ksmbd_conn_wq, &conn->release_work);
+}
+
+/**
+ * ksmbd_conn_free() - free resources of the connection instance
+ *
+ * @conn:	connection instance to be cleaned up
+ *
+ * During the thread termination, the corresponding conn instance
+ * resources(sock/memory) are released and finally the conn object is freed.
+ */
+void ksmbd_conn_free(struct ksmbd_conn *conn)
+{
+	down_write(&conn_list_lock);
+	hash_del(&conn->hlist);
+	up_write(&conn_list_lock);
+
+	/*
+	 * request_buf / preauth_info / mechToken are only ever accessed by the
+	 * connection handler thread that owns @conn.  ksmbd_conn_free() is
+	 * called from the transport free_transport() path when that thread is
+	 * exiting, so it is safe to release them unconditionally even when
+	 * ksmbd_conn_put() below is not the final putter (oplock / ksmbd_file
+	 * holders only retain the conn pointer, not these per-thread buffers).
+	 */
+	xa_destroy(&conn->sessions);
+	kvfree(conn->request_buf);
+	kfree_sensitive(conn->preauth_info);
+	kfree(conn->mechToken);
+	ksmbd_preauth_session_destroy(conn);
+	ksmbd_conn_put(conn);
+}
+
+/**
+ * ksmbd_conn_alloc() - initialize a new connection instance
+ *
+ * Return:	ksmbd_conn struct on success, otherwise NULL
+ */
+struct ksmbd_conn *ksmbd_conn_alloc(void)
+{
+	struct ksmbd_conn *conn;
+
+	conn = kzalloc_obj(struct ksmbd_conn, KSMBD_DEFAULT_GFP);
+	if (!conn)
+		return NULL;
+
+	conn->need_neg = true;
+	ksmbd_conn_set_new(conn);
+	conn->local_nls = load_nls("utf8");
+	if (!conn->local_nls)
+		conn->local_nls = load_nls_default();
+	if (IS_ENABLED(CONFIG_UNICODE))
+		conn->um = utf8_load(UNICODE_AGE(12, 1, 0));
+	else
+		conn->um = ERR_PTR(-EOPNOTSUPP);
+	if (IS_ERR(conn->um))
+		conn->um = NULL;
+	INIT_WORK(&conn->release_work, __ksmbd_conn_release_work);
+	atomic_set(&conn->req_running, 0);
+	atomic_set(&conn->r_count, 0);
+	atomic_set(&conn->refcnt, 1);
+	conn->total_credits = 1;
+	conn->outstanding_credits = 0;
+
+	/*
+	 * The command sequence window starts as the set { 0 } when the
+	 * connection is established.
+	 */
+	conn->seq_low = 0;
+	conn->seq_high = 1;
+	__set_bit(0, conn->seq_bitmap);
+
+	init_waitqueue_head(&conn->req_running_q);
+	init_waitqueue_head(&conn->r_count_q);
+	INIT_LIST_HEAD(&conn->requests);
+	INIT_LIST_HEAD(&conn->async_requests);
+	INIT_LIST_HEAD(&conn->preauth_sess_table);
+	spin_lock_init(&conn->request_lock);
+	spin_lock_init(&conn->credits_lock);
+	ida_init(&conn->async_ida);
+	xa_init(&conn->sessions);
+
+	spin_lock_init(&conn->llist_lock);
+	INIT_LIST_HEAD(&conn->lock_list);
+
+	init_rwsem(&conn->session_lock);
+
+	return conn;
+}
+
+bool ksmbd_conn_lookup_dialect(struct ksmbd_conn *c)
+{
+	struct ksmbd_conn *t;
+	int bkt;
+	bool ret = false;
+
+	down_read(&conn_list_lock);
+	hash_for_each(conn_list, bkt, t, hlist) {
+		if (memcmp(t->ClientGUID, c->ClientGUID, SMB2_CLIENT_GUID_SIZE))
+			continue;
+
+		ret = true;
+		break;
+	}
+	up_read(&conn_list_lock);
+	return ret;
+}
+
+void ksmbd_conn_enqueue_request(struct ksmbd_work *work)
+{
+	struct ksmbd_conn *conn = work->conn;
+	struct list_head *requests_queue = NULL;
+
+	if (conn->ops->get_cmd_val(work) != SMB2_CANCEL_HE)
+		requests_queue = &conn->requests;
+
+	atomic_inc(&conn->req_running);
+	if (requests_queue) {
+		spin_lock(&conn->request_lock);
+		list_add_tail(&work->request_entry, requests_queue);
+		spin_unlock(&conn->request_lock);
+	}
+}
+
+void ksmbd_conn_try_dequeue_request(struct ksmbd_work *work)
+{
+	struct ksmbd_conn *conn = work->conn;
+
+	atomic_dec(&conn->req_running);
+	if (waitqueue_active(&conn->req_running_q))
+		wake_up(&conn->req_running_q);
+
+	if (list_empty(&work->request_entry) &&
+	    list_empty(&work->async_request_entry))
+		return;
+
+	spin_lock(&conn->request_lock);
+	list_del_init(&work->request_entry);
+	spin_unlock(&conn->request_lock);
+	if (work->asynchronous)
+		release_async_work(work);
+
+	wake_up_all(&conn->req_running_q);
+}
+
+static void ksmbd_conn_cancel_async_requests(struct ksmbd_conn *conn)
+{
+	struct ksmbd_work *work, *tmp;
+
+	ksmbd_debug(CONN, "Cancel pending async requests on releasing connection\n");
+	spin_lock(&conn->request_lock);
+	list_for_each_entry_safe(work, tmp, &conn->async_requests,
+				 async_request_entry) {
+		if (cmpxchg(&work->state, KSMBD_WORK_ACTIVE,
+			    KSMBD_WORK_CANCELLED) != KSMBD_WORK_ACTIVE)
+			continue;
+
+		ksmbd_debug(CONN, "Cancel async request id %d\n",
+			    work->async_id);
+		if (work->cancel_fn)
+			work->cancel_fn(work->cancel_argv);
+	}
+	spin_unlock(&conn->request_lock);
+}
+
+void ksmbd_conn_lock(struct ksmbd_conn *conn)
+{
+	mutex_lock(&conn->srv_mutex);
+}
+
+void ksmbd_conn_unlock(struct ksmbd_conn *conn)
+{
+	mutex_unlock(&conn->srv_mutex);
+}
+
+static bool ksmbd_session_is_bound_to_conn(struct ksmbd_session *sess,
+					   struct ksmbd_conn *conn)
+{
+	bool found;
+
+	rcu_read_lock();
+	found = xa_load(&conn->sessions, sess->id) == sess;
+	rcu_read_unlock();
+	if (found)
+		return true;
+
+	down_read(&sess->chann_lock);
+	found = xa_load(&sess->ksmbd_chann_list, (long)conn);
+	up_read(&sess->chann_lock);
+	return found;
+}
+
+void ksmbd_all_conn_set_status(struct ksmbd_session *sess, u32 status)
+{
+	struct ksmbd_conn *conn;
+	int bkt;
+
+	down_read(&conn_list_lock);
+	hash_for_each(conn_list, bkt, conn, hlist) {
+		if (ksmbd_session_is_bound_to_conn(sess, conn)) {
+			spin_lock(&conn->request_lock);
+			if (!ksmbd_conn_exiting(conn) &&
+			    !ksmbd_conn_releasing(conn))
+				WRITE_ONCE(conn->status, status);
+			spin_unlock(&conn->request_lock);
+		}
+	}
+	up_read(&conn_list_lock);
+}
+
+void ksmbd_conn_abort(struct ksmbd_conn *conn)
+{
+	bool shutdown = false;
+
+	spin_lock(&conn->request_lock);
+	if (!ksmbd_conn_exiting(conn) && !ksmbd_conn_releasing(conn)) {
+		ksmbd_conn_set_exiting(conn);
+		shutdown = true;
+	}
+	spin_unlock(&conn->request_lock);
+	wake_up_all(&conn->req_running_q);
+
+	if (shutdown && conn->transport->ops->shutdown)
+		conn->transport->ops->shutdown(conn->transport);
+}
+
+void ksmbd_conn_wait_idle(struct ksmbd_conn *conn)
+{
+	wait_event(conn->req_running_q, atomic_read(&conn->req_running) < 2);
+}
+
+int ksmbd_conn_wait_idle_sess(struct ksmbd_conn *curr_conn,
+			      struct ksmbd_session *sess)
+{
+	struct ksmbd_conn *conn;
+	int rc, retry_count = 0, max_timeout = 120;
+	int rcount, bkt;
+
+retry_idle:
+	if (retry_count >= max_timeout)
+		return -EIO;
+
+	/* A blocked byte-range lock cannot drain until teardown wakes it. */
+	ksmbd_wake_session_blocked_works(sess);
+
+	down_read(&conn_list_lock);
+	hash_for_each(conn_list, bkt, conn, hlist) {
+		if (ksmbd_session_is_bound_to_conn(sess, conn)) {
+			rcount = (conn == curr_conn) ? 2 : 1;
+			if (atomic_read(&conn->req_running) >= rcount) {
+				rc = wait_event_timeout(conn->req_running_q,
+					atomic_read(&conn->req_running) < rcount,
+					HZ);
+				if (!rc) {
+					up_read(&conn_list_lock);
+					retry_count++;
+					goto retry_idle;
+				}
+			}
+		}
+	}
+	up_read(&conn_list_lock);
+
+	return 0;
+}
+
+static int __ksmbd_conn_write(struct ksmbd_work *work,
+			      struct ksmbd_transport_write *tx)
+{
+	struct ksmbd_conn *conn = work->conn;
+	int sent;
+
+	if (!work->response_buf) {
+		pr_err("NULL response header\n");
+		return -EINVAL;
+	}
+
+	if (work->send_no_response)
+		return 0;
+
+	if (!work->iov_idx)
+		return -EINVAL;
+
+	tx->iov = work->iov;
+	tx->iov_cnt = work->iov_cnt;
+	tx->size = get_rfc1002_len(work->iov[0].iov_base) + 4;
+	tx->need_invalidate_rkey = work->need_invalidate_rkey;
+	tx->remote_key = work->remote_key;
+
+	ksmbd_conn_lock(conn);
+	sent = conn->transport->ops->writev(conn->transport, tx);
+	ksmbd_conn_unlock(conn);
+
+	if (sent < 0) {
+		pr_err("Failed to send message: %d\n", sent);
+		return sent;
+	}
+
+	return 0;
+}
+
+int ksmbd_conn_write(struct ksmbd_work *work)
+{
+	struct ksmbd_transport_write tx = {};
+
+	return __ksmbd_conn_write(work, &tx);
+}
+
+int ksmbd_conn_write_eor(struct ksmbd_work *work)
+{
+	struct ksmbd_transport_write tx = {
+		.msg_flags = MSG_EOR,
+	};
+
+	return __ksmbd_conn_write(work, &tx);
+}
+
+int ksmbd_conn_rdma_read(struct ksmbd_conn *conn,
+			 void *buf, unsigned int buflen,
+			 struct smbdirect_buffer_descriptor_v1 *desc,
+			 unsigned int desc_len)
+{
+	int ret = -EINVAL;
+
+	if (conn->transport->ops->rdma_read)
+		ret = conn->transport->ops->rdma_read(conn->transport,
+						      buf, buflen,
+						      desc, desc_len);
+	return ret;
+}
+
+int ksmbd_conn_rdma_write(struct ksmbd_conn *conn,
+			  void *buf, unsigned int buflen,
+			  struct smbdirect_buffer_descriptor_v1 *desc,
+			  unsigned int desc_len)
+{
+	int ret = -EINVAL;
+
+	if (conn->transport->ops->rdma_write)
+		ret = conn->transport->ops->rdma_write(conn->transport,
+						       buf, buflen,
+						       desc, desc_len);
+	return ret;
+}
+
+bool ksmbd_conn_alive(struct ksmbd_conn *conn)
+{
+	if (!ksmbd_server_running())
+		return false;
+
+	if (ksmbd_conn_exiting(conn))
+		return false;
+
+	if (kthread_should_stop())
+		return false;
+
+	if (atomic_read(&conn->stats.open_files_count) > 0)
+		return true;
+
+	/*
+	 * Stop current session if the time that get last request from client
+	 * is bigger than deadtime user configured and opening file count is
+	 * zero.
+	 */
+	if (server_conf.deadtime > 0 &&
+	    time_after(jiffies, conn->last_active + server_conf.deadtime)) {
+		ksmbd_debug(CONN, "No response from client in %lu minutes\n",
+			    server_conf.deadtime / SMB_ECHO_INTERVAL);
+		return false;
+	}
+	return true;
+}
+
+/* "+2" for BCC field (ByteCount, 2 bytes) */
+#define SMB1_MIN_SUPPORTED_PDU_SIZE (sizeof(struct smb_hdr) + 2)
+#define SMB2_MIN_SUPPORTED_PDU_SIZE (sizeof(struct smb2_pdu))
+#define SMB2_TRANSFORM_MIN_SUPPORTED_PDU_SIZE	\
+	(sizeof(struct smb2_transform_hdr) + sizeof(struct smb2_hdr))
+
+/**
+ * ksmbd_conn_handler_loop() - session thread to listen on new smb requests
+ * @p:		connection instance
+ *
+ * One thread each per connection
+ *
+ * Return:	0 on success
+ */
+int ksmbd_conn_handler_loop(void *p)
+{
+	struct ksmbd_conn *conn = (struct ksmbd_conn *)p;
+	struct ksmbd_transport *t = conn->transport;
+	unsigned int pdu_size, max_allowed_pdu_size, max_req;
+	__le32 proto;
+	char hdr_buf[4] = {0,};
+	int size;
+
+	mutex_init(&conn->srv_mutex);
+	__module_get(THIS_MODULE);
+
+	max_req = server_conf.max_inflight_req;
+	conn->last_active = jiffies;
+	set_freezable();
+	while (ksmbd_conn_alive(conn)) {
+		if (try_to_freeze())
+			continue;
+
+		kvfree(conn->request_buf);
+		conn->request_buf = NULL;
+
+recheck:
+		if (atomic_read(&conn->req_running) + 1 > max_req) {
+			wait_event_interruptible(conn->req_running_q,
+				atomic_read(&conn->req_running) < max_req);
+			goto recheck;
+		}
+
+		size = t->ops->read(t, hdr_buf, sizeof(hdr_buf), -1);
+		if (size != sizeof(hdr_buf))
+			break;
+
+		pdu_size = get_rfc1002_len(hdr_buf);
+		ksmbd_debug(CONN, "RFC1002 header %u bytes\n", pdu_size);
+
+		max_allowed_pdu_size = ksmbd_max_allowed_pdu_size(conn);
+
+		if (pdu_size > max_allowed_pdu_size) {
+			pr_err_ratelimited("PDU length(%u) exceeded maximum allowed pdu size(%u) on connection(%d)\n",
+					pdu_size, max_allowed_pdu_size,
+					READ_ONCE(conn->status));
+			break;
+		}
+
+		/*
+		 * Check maximum pdu size(0x00FFFFFF).
+		 */
+		if (pdu_size > MAX_STREAM_PROT_LEN)
+			break;
+
+		if (pdu_size < SMB1_MIN_SUPPORTED_PDU_SIZE)
+			break;
+
+		/* 4 for rfc1002 length field */
+		/* 1 for implied bcc[0] */
+		size = pdu_size + 4 + 1;
+		conn->request_buf = kvmalloc(size, KSMBD_DEFAULT_GFP);
+		if (!conn->request_buf)
+			break;
+
+		memcpy(conn->request_buf, hdr_buf, sizeof(hdr_buf));
+
+		/*
+		 * We already read 4 bytes to find out PDU size, now
+		 * read in PDU
+		 */
+		size = t->ops->read(t, conn->request_buf + 4, pdu_size, 2);
+		if (size < 0) {
+			pr_err("sock_read failed: %d\n", size);
+			break;
+		}
+
+		if (size != pdu_size) {
+			pr_err("PDU error. Read: %d, Expected: %d\n",
+			       size, pdu_size);
+			continue;
+		}
+
+		if (((struct smb2_hdr *)smb_get_msg(conn->request_buf))->ProtocolId ==
+		    SMB2_COMPRESSION_TRANSFORM_ID) {
+			/*
+			 * Convert the transform into a normal RFC1002-framed SMB2
+			 * request before protocol validation and work allocation.
+			 */
+			if (ksmbd_decompress_request(conn))
+				break;
+			pdu_size = get_rfc1002_len(conn->request_buf);
+		}
+
+		if (!ksmbd_smb_request(conn))
+			break;
+
+		proto = *(__le32 *)smb_get_msg(conn->request_buf);
+		if (proto == SMB2_PROTO_NUMBER &&
+		    pdu_size < SMB2_MIN_SUPPORTED_PDU_SIZE)
+			break;
+
+		if (proto == SMB2_TRANSFORM_PROTO_NUM &&
+		    pdu_size < SMB2_TRANSFORM_MIN_SUPPORTED_PDU_SIZE)
+			break;
+
+		if (!default_conn_ops.process_fn) {
+			pr_err("No connection request callback\n");
+			break;
+		}
+
+		if (default_conn_ops.process_fn(conn)) {
+			pr_err("Cannot handle request\n");
+			break;
+		}
+	}
+
+	ksmbd_conn_set_releasing(conn);
+	ksmbd_conn_cancel_async_requests(conn);
+	/* Wait till all reference dropped to the Server object*/
+	ksmbd_debug(CONN, "Wait for all pending requests(%d)\n", atomic_read(&conn->r_count));
+	wait_event(conn->r_count_q, atomic_read(&conn->r_count) == 0);
+
+	if (IS_ENABLED(CONFIG_UNICODE))
+		utf8_unload(conn->um);
+	unload_nls(conn->local_nls);
+	if (default_conn_ops.terminate_fn)
+		default_conn_ops.terminate_fn(conn);
+	t->ops->disconnect(t);
+	module_put(THIS_MODULE);
+	return 0;
+}
+
+void ksmbd_conn_init_server_callbacks(struct ksmbd_conn_ops *ops)
+{
+	default_conn_ops.process_fn = ops->process_fn;
+	default_conn_ops.terminate_fn = ops->terminate_fn;
+}
+
+void ksmbd_conn_r_count_inc(struct ksmbd_conn *conn)
+{
+	atomic_inc(&conn->r_count);
+}
+
+void ksmbd_conn_r_count_dec(struct ksmbd_conn *conn)
+{
+	/*
+	 * Checking waitqueue to dropping pending requests on
+	 * disconnection. waitqueue_active is safe because it
+	 * uses atomic operation for condition.
+	 */
+	atomic_inc(&conn->refcnt);
+	if (!atomic_dec_return(&conn->r_count) && waitqueue_active(&conn->r_count_q))
+		wake_up(&conn->r_count_q);
+
+	ksmbd_conn_put(conn);
+}
+
+int ksmbd_conn_transport_init(void)
+{
+	int ret;
+
+	mutex_lock(&init_lock);
+	ret = ksmbd_tcp_init();
+	if (ret) {
+		pr_err("Failed to init TCP subsystem: %d\n", ret);
+		goto out;
+	}
+
+	ret = ksmbd_rdma_init();
+	if (ret) {
+		pr_err("Failed to init RDMA subsystem: %d\n", ret);
+		goto out;
+	}
+out:
+	mutex_unlock(&init_lock);
+	if (create_proc_clients())
+		pr_warn("Unable to create clients procfs entry\n");
+	return ret;
+}
+
+static void stop_sessions(void)
+{
+	struct ksmbd_conn *conn, *target;
+	struct ksmbd_transport *t;
+	bool any;
+	int bkt;
+
+	/*
+	 * Serialised via init_lock; no concurrent stop_sessions() can
+	 * touch conn->stop_called, so writing it under the read lock is
+	 * safe.
+	 */
+again:
+	target = NULL;
+	any = false;
+	down_read(&conn_list_lock);
+	hash_for_each(conn_list, bkt, conn, hlist) {
+		any = true;
+		if (conn->stop_called)
+			continue;
+		atomic_inc(&conn->refcnt);
+		conn->stop_called = true;
+		/*
+		 * Mark the connection EXITING while still holding the
+		 * read lock so the selection and the status transition
+		 * happen together.  Do not regress a connection that has
+		 * already advanced to RELEASING on its own (e.g. the
+		 * handler exited its receive loop for an unrelated
+		 * reason).
+		 */
+		spin_lock(&conn->request_lock);
+		if (!ksmbd_conn_releasing(conn))
+			ksmbd_conn_set_exiting(conn);
+		spin_unlock(&conn->request_lock);
+		target = conn;
+		break;
+	}
+	up_read(&conn_list_lock);
+
+	if (target) {
+		t = target->transport;
+		if (t->ops->shutdown)
+			t->ops->shutdown(t);
+		if (atomic_dec_and_test(&target->refcnt)) {
+			ida_destroy(&target->async_ida);
+			t->ops->free_transport(t);
+			kfree_sensitive(target);
+		}
+		goto again;
+	}
+
+	if (any) {
+		msleep(100);
+		goto again;
+	}
+}
+
+void ksmbd_conn_transport_destroy(void)
+{
+	delete_proc_clients();
+	mutex_lock(&init_lock);
+	ksmbd_tcp_destroy();
+	ksmbd_rdma_stop_listening();
+	stop_sessions();
+	mutex_unlock(&init_lock);
+}