bpf: mark a NULL kfunc argument precisegrafted

check_kfunc_arg() allows bpf_register_is_null() for nullable arguments
w/o marking the underlying scalar register precise. Hence a checkpoint
created on such a path would prune against arbitrary scalar value.

Fixes: 3bda08b63670 ("bpf: Allow NULL buffers in bpf_dynptr_slice(_rw)")
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260904-register-is-null-precise-fixes-v1-5-0f5a360ff15d@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.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);