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, 74 insertions, 0 deletions

diff --git a/net/llc/llc_output.c b/net/llc/llc_output.c
new file mode 100644
index 000000000..5a6466fc6
--- /dev/null
+++ b/net/llc/llc_output.c
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * llc_output.c - LLC minimal output path
+ *
+ * Copyright (c) 1997 by Procom Technology, Inc.
+ * 		 2001-2003 by Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+
+#include <linux/if_arp.h>
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <linux/export.h>
+#include <net/llc.h>
+#include <net/llc_pdu.h>
+
+/**
+ *	llc_mac_hdr_init - fills MAC header fields
+ *	@skb: Address of the frame to initialize its MAC header
+ *	@sa: The MAC source address
+ *	@da: The MAC destination address
+ *
+ *	Fills MAC header fields, depending on MAC type. Returns 0, If MAC type
+ *	is a valid type and initialization completes correctly 1, otherwise.
+ */
+int llc_mac_hdr_init(struct sk_buff *skb,
+		     const unsigned char *sa, const unsigned char *da)
+{
+	int rc = -EINVAL;
+
+	switch (skb->dev->type) {
+	case ARPHRD_ETHER:
+	case ARPHRD_LOOPBACK:
+		rc = dev_hard_header(skb, skb->dev, ETH_P_802_2, da, sa,
+				     skb->len);
+		if (rc > 0)
+			rc = 0;
+		break;
+	default:
+		break;
+	}
+	return rc;
+}
+
+/**
+ *	llc_build_and_send_ui_pkt - unitdata request interface for upper layers
+ *	@sap: sap to use
+ *	@skb: packet to send
+ *	@dmac: destination mac address
+ *	@dsap: destination sap
+ *
+ *	Upper layers calls this function when upper layer wants to send data
+ *	using connection-less mode communication (UI pdu).
+ *
+ *	Accept data frame from network layer to be sent using connection-
+ *	less mode communication; timeout/retries handled by network layer;
+ *	package primitive as an event and send to SAP event handler
+ */
+int llc_build_and_send_ui_pkt(struct llc_sap *sap, struct sk_buff *skb,
+			      const unsigned char *dmac, unsigned char dsap)
+{
+	int rc;
+	llc_pdu_header_init(skb, LLC_PDU_TYPE_U, sap->laddr.lsap,
+			    dsap, LLC_PDU_CMD);
+	llc_pdu_init_as_ui_cmd(skb);
+	rc = llc_mac_hdr_init(skb, skb->dev->dev_addr, dmac);
+	if (likely(!rc))
+		rc = dev_queue_xmit(skb);
+	else
+		kfree_skb(skb);
+	return rc;
+}
+
+EXPORT_SYMBOL(llc_mac_hdr_init);
+EXPORT_SYMBOL(llc_build_and_send_ui_pkt);