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, 94 insertions, 0 deletions

diff --git a/include/net/seg6.h b/include/net/seg6.h
new file mode 100644
index 000000000..82b3fbbcb
--- /dev/null
+++ b/include/net/seg6.h
@@ -0,0 +1,94 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ *  SR-IPv6 implementation
+ *
+ *  Author:
+ *  David Lebrun <david.lebrun@uclouvain.be>
+ */
+
+#ifndef _NET_SEG6_H
+#define _NET_SEG6_H
+
+#include <linux/net.h>
+#include <linux/ipv6.h>
+#include <linux/seg6.h>
+#include <linux/rhashtable-types.h>
+
+static inline void update_csum_diff4(struct sk_buff *skb, __be32 from,
+				     __be32 to)
+{
+	__be32 diff[] = { ~from, to };
+
+	skb->csum = ~csum_partial((char *)diff, sizeof(diff), ~skb->csum);
+}
+
+static inline void update_csum_diff16(struct sk_buff *skb, __be32 *from,
+				      __be32 *to)
+{
+	__be32 diff[] = {
+		~from[0], ~from[1], ~from[2], ~from[3],
+		to[0], to[1], to[2], to[3],
+	};
+
+	skb->csum = ~csum_partial((char *)diff, sizeof(diff), ~skb->csum);
+}
+
+struct seg6_pernet_data {
+	struct mutex lock;
+	struct in6_addr __rcu *tun_src;
+#ifdef CONFIG_IPV6_SEG6_HMAC
+	struct rhashtable hmac_infos;
+#endif
+};
+
+static inline struct seg6_pernet_data *seg6_pernet(struct net *net)
+{
+#if IS_ENABLED(CONFIG_IPV6)
+	return net->ipv6.seg6_data;
+#else
+	return NULL;
+#endif
+}
+
+extern int seg6_init(void);
+extern void seg6_exit(void);
+#ifdef CONFIG_IPV6_SEG6_LWTUNNEL
+extern int seg6_iptunnel_init(void);
+extern void seg6_iptunnel_exit(void);
+extern int seg6_local_init(void);
+extern void seg6_local_exit(void);
+#else
+static inline int seg6_iptunnel_init(void) { return 0; }
+static inline void seg6_iptunnel_exit(void) {}
+static inline int seg6_local_init(void) { return 0; }
+static inline void seg6_local_exit(void) {}
+#endif
+
+extern bool seg6_validate_srh(struct ipv6_sr_hdr *srh, int len, bool reduced);
+extern struct ipv6_sr_hdr *seg6_get_srh(struct sk_buff *skb, int flags);
+extern void seg6_icmp_srh(struct sk_buff *skb, struct inet6_skb_parm *opt);
+extern int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh,
+			     int proto);
+extern int seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh);
+extern int seg6_lookup_nexthop(struct sk_buff *skb, struct in6_addr *nhaddr,
+			       u32 tbl_id);
+
+/* If the packet which invoked an ICMP error contains an SRH return
+ * the true destination address from within the SRH, otherwise use the
+ * destination address in the IP header.
+ */
+static inline const struct in6_addr *seg6_get_daddr(struct sk_buff *skb,
+						    struct inet6_skb_parm *opt)
+{
+	struct ipv6_sr_hdr *srh;
+
+	if (opt->flags & IP6SKB_SEG6) {
+		srh = (struct ipv6_sr_hdr *)(skb->data + opt->srhoff);
+		return  &srh->segments[0];
+	}
+
+	return NULL;
+}
+
+
+#endif