selftests/bpf: Test packet range of pointers sharing an idgrafted

Add tests where two packet pointers share an id and tightening one
pointer's umax from its var_off would put it less than their constant
distance from the other's umax: with an index & 0x38 capped at 50, the
base pointer keeps umax 50, so the pointer 8 bytes further on must keep
umax 58, even though its known bits allow at most 56.

These refused a valid program or accepted an out-of-bounds access before
the fix:

- check the advanced copy, load through the base: valid, was refused;
- check the base, load the byte at base + 1 through a copy advanced by
  8: was accepted;
- check base + 4, load 4 bytes at base + 2 through base + 8: reads two
  bytes past the checked range, was accepted;
- the same as the second with data_meta pointers checked against data:
  was accepted.

These pass with and without the fix and cover nearby paths:

- subtract an unknown scalar from a checked pointer and load below it
  (the range is kept across a new id);
- reach a load through two paths whose checks cover 8 and 7 bytes after
  the loaded pointer; the second path must not be pruned by the first;
- spill a copy of a pointer, check the pointer, fill the copy and load
  one byte past the checked range: the load is refused, and the copy
  has the range of the check.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20261001145255.855630-2-alexei.starovoitov@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

1 files changed, 77 insertions, 0 deletions

diff --git a/include/net/arp.h b/include/net/arp.h
new file mode 100644
index 000000000..e8747e071
--- /dev/null
+++ b/include/net/arp.h
@@ -0,0 +1,77 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* linux/net/inet/arp.h */
+#ifndef _ARP_H
+#define _ARP_H
+
+#include <linux/if_arp.h>
+#include <linux/hash.h>
+#include <net/neighbour.h>
+
+
+extern struct neigh_table arp_tbl;
+
+static inline u32 arp_hashfn(const void *pkey, const struct net_device *dev, u32 *hash_rnd)
+{
+	u32 key = *(const u32 *)pkey;
+	u32 val = key ^ hash32_ptr(dev);
+
+	return val * hash_rnd[0];
+}
+
+#ifdef CONFIG_INET
+static inline struct neighbour *__ipv4_neigh_lookup_noref(struct net_device *dev, u32 key)
+{
+	if (dev->flags & (IFF_LOOPBACK | IFF_POINTOPOINT))
+		key = INADDR_ANY;
+
+	return ___neigh_lookup_noref(&arp_tbl, neigh_key_eq32, arp_hashfn, &key, dev);
+}
+#else
+static inline
+struct neighbour *__ipv4_neigh_lookup_noref(struct net_device *dev, u32 key)
+{
+	return NULL;
+}
+#endif
+
+static inline struct neighbour *__ipv4_neigh_lookup(struct net_device *dev, u32 key)
+{
+	struct neighbour *n;
+
+	rcu_read_lock();
+	n = __ipv4_neigh_lookup_noref(dev, key);
+	if (n && !refcount_inc_not_zero(&n->refcnt))
+		n = NULL;
+	rcu_read_unlock();
+
+	return n;
+}
+
+static inline void __ipv4_confirm_neigh(struct net_device *dev, u32 key)
+{
+	struct neighbour *n;
+
+	rcu_read_lock();
+	n = __ipv4_neigh_lookup_noref(dev, key);
+	neigh_confirm(n);
+	rcu_read_unlock();
+}
+
+void arp_init(void);
+int arp_ioctl(struct net *net, unsigned int cmd, void __user *arg);
+void arp_send(int type, int ptype, __be32 dest_ip,
+	      struct net_device *dev, __be32 src_ip,
+	      const unsigned char *dest_hw,
+	      const unsigned char *src_hw, const unsigned char *th);
+int arp_mc_map(__be32 addr, u8 *haddr, struct net_device *dev, int dir);
+void arp_ifdown(struct net_device *dev);
+int arp_invalidate(struct net_device *dev, __be32 ip, bool force);
+
+struct sk_buff *arp_create(int type, int ptype, __be32 dest_ip,
+			   struct net_device *dev, __be32 src_ip,
+			   const unsigned char *dest_hw,
+			   const unsigned char *src_hw,
+			   const unsigned char *target_hw);
+void arp_xmit(struct sk_buff *skb);
+
+#endif	/* _ARP_H */