ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 79 insertions, 0 deletions

diff --git a/net/sched/em_nbyte.c b/net/sched/em_nbyte.c
new file mode 100644
index 000000000..c65ffa5ff
--- /dev/null
+++ b/net/sched/em_nbyte.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * net/sched/em_nbyte.c	N-Byte ematch
+ *
+ * Authors:	Thomas Graf <tgraf@suug.ch>
+ */
+
+#include <linux/gfp.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/skbuff.h>
+#include <linux/tc_ematch/tc_em_nbyte.h>
+#include <net/pkt_cls.h>
+
+struct nbyte_data {
+	struct tcf_em_nbyte	hdr;
+	char			pattern[];
+};
+
+static int em_nbyte_change(struct net *net, void *data, int data_len,
+			   struct tcf_ematch *em)
+{
+	struct tcf_em_nbyte *nbyte = data;
+
+	if (data_len < sizeof(*nbyte) ||
+	    data_len < (sizeof(*nbyte) + nbyte->len))
+		return -EINVAL;
+
+	em->datalen = sizeof(*nbyte) + nbyte->len;
+	em->data = (unsigned long)kmemdup(data, em->datalen, GFP_KERNEL);
+	if (em->data == 0UL)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static int em_nbyte_match(struct sk_buff *skb, struct tcf_ematch *em,
+			  struct tcf_pkt_info *info)
+{
+	struct nbyte_data *nbyte = (struct nbyte_data *) em->data;
+	unsigned char *ptr = tcf_get_base_ptr(skb, nbyte->hdr.layer);
+
+	if (!ptr)
+		return 0;
+	ptr += nbyte->hdr.off;
+
+	if (!tcf_valid_offset(skb, ptr, nbyte->hdr.len))
+		return 0;
+
+	return !memcmp(ptr, nbyte->pattern, nbyte->hdr.len);
+}
+
+static struct tcf_ematch_ops em_nbyte_ops = {
+	.kind	  = TCF_EM_NBYTE,
+	.change	  = em_nbyte_change,
+	.match	  = em_nbyte_match,
+	.owner	  = THIS_MODULE,
+	.link	  = LIST_HEAD_INIT(em_nbyte_ops.link)
+};
+
+static int __init init_em_nbyte(void)
+{
+	return tcf_em_register(&em_nbyte_ops);
+}
+
+static void __exit exit_em_nbyte(void)
+{
+	tcf_em_unregister(&em_nbyte_ops);
+}
+
+MODULE_DESCRIPTION("ematch classifier for arbitrary skb multi-bytes");
+MODULE_LICENSE("GPL");
+
+module_init(init_em_nbyte);
+module_exit(exit_em_nbyte);
+
+MODULE_ALIAS_TCF_EMATCH(TCF_EM_NBYTE);