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, 99 insertions, 0 deletions

diff --git a/net/sched/em_cmp.c b/net/sched/em_cmp.c
new file mode 100644
index 000000000..48c1bce74
--- /dev/null
+++ b/net/sched/em_cmp.c
@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * net/sched/em_cmp.c	Simple packet data comparison ematch
+ *
+ * Authors:	Thomas Graf <tgraf@suug.ch>
+ */
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/skbuff.h>
+#include <linux/tc_ematch/tc_em_cmp.h>
+#include <linux/unaligned.h>
+#include <net/pkt_cls.h>
+
+static inline int cmp_needs_transformation(struct tcf_em_cmp *cmp)
+{
+	return unlikely(cmp->flags & TCF_EM_CMP_TRANS);
+}
+
+static int em_cmp_match(struct sk_buff *skb, struct tcf_ematch *em,
+			struct tcf_pkt_info *info)
+{
+	struct tcf_em_cmp *cmp = (struct tcf_em_cmp *) em->data;
+	unsigned char *ptr = tcf_get_base_ptr(skb, cmp->layer);
+	u32 val = 0;
+
+	if (!ptr)
+		return 0;
+	ptr += cmp->off;
+	if (!tcf_valid_offset(skb, ptr, cmp->align))
+		return 0;
+
+	switch (cmp->align) {
+	case TCF_EM_ALIGN_U8:
+		val = *ptr;
+		break;
+
+	case TCF_EM_ALIGN_U16:
+		val = get_unaligned_be16(ptr);
+
+		if (cmp_needs_transformation(cmp))
+			val = be16_to_cpu(val);
+		break;
+
+	case TCF_EM_ALIGN_U32:
+		/* Worth checking boundaries? The branching seems
+		 * to get worse. Visit again.
+		 */
+		val = get_unaligned_be32(ptr);
+
+		if (cmp_needs_transformation(cmp))
+			val = be32_to_cpu(val);
+		break;
+
+	default:
+		return 0;
+	}
+
+	if (cmp->mask)
+		val &= cmp->mask;
+
+	switch (cmp->opnd) {
+	case TCF_EM_OPND_EQ:
+		return val == cmp->val;
+	case TCF_EM_OPND_LT:
+		return val < cmp->val;
+	case TCF_EM_OPND_GT:
+		return val > cmp->val;
+	}
+
+	return 0;
+}
+
+static struct tcf_ematch_ops em_cmp_ops = {
+	.kind	  = TCF_EM_CMP,
+	.datalen  = sizeof(struct tcf_em_cmp),
+	.match	  = em_cmp_match,
+	.owner	  = THIS_MODULE,
+	.link	  = LIST_HEAD_INIT(em_cmp_ops.link)
+};
+
+static int __init init_em_cmp(void)
+{
+	return tcf_em_register(&em_cmp_ops);
+}
+
+static void __exit exit_em_cmp(void)
+{
+	tcf_em_unregister(&em_cmp_ops);
+}
+
+MODULE_DESCRIPTION("ematch classifier for basic data types(8/16/32 bit) against skb data");
+MODULE_LICENSE("GPL");
+
+module_init(init_em_cmp);
+module_exit(exit_em_cmp);
+
+MODULE_ALIAS_TCF_EMATCH(TCF_EM_CMP);