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, 145 insertions, 0 deletions

diff --git a/include/net/gre.h b/include/net/gre.h
new file mode 100644
index 000000000..b55f67ecd
--- /dev/null
+++ b/include/net/gre.h
@@ -0,0 +1,145 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_GRE_H
+#define __LINUX_GRE_H
+
+#include <linux/skbuff.h>
+#include <net/ip_tunnels.h>
+
+struct gre_base_hdr {
+	__be16 flags;
+	__be16 protocol;
+} __packed;
+
+struct gre_full_hdr {
+	struct gre_base_hdr fixed_header;
+	__be16 csum;
+	__be16 reserved1;
+	__be32 key;
+	__be32 seq;
+} __packed;
+#define GRE_HEADER_SECTION 4
+
+#define GREPROTO_CISCO		0
+#define GREPROTO_PPTP		1
+#define GREPROTO_MAX		2
+#define GRE_IP_PROTO_MAX	2
+
+struct gre_protocol {
+	int  (*handler)(struct sk_buff *skb);
+	void (*err_handler)(struct sk_buff *skb, u32 info);
+};
+
+int gre_add_protocol(const struct gre_protocol *proto, u8 version);
+int gre_del_protocol(const struct gre_protocol *proto, u8 version);
+
+int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
+		     bool *csum_err, __be16 proto, int nhs);
+
+static inline bool netif_is_gretap(const struct net_device *dev)
+{
+	return dev->rtnl_link_ops &&
+	       !strcmp(dev->rtnl_link_ops->kind, "gretap");
+}
+
+static inline bool netif_is_ip6gretap(const struct net_device *dev)
+{
+	return dev->rtnl_link_ops &&
+	       !strcmp(dev->rtnl_link_ops->kind, "ip6gretap");
+}
+
+static inline int gre_calc_hlen(const unsigned long *o_flags)
+{
+	int addend = 4;
+
+	if (test_bit(IP_TUNNEL_CSUM_BIT, o_flags))
+		addend += 4;
+	if (test_bit(IP_TUNNEL_KEY_BIT, o_flags))
+		addend += 4;
+	if (test_bit(IP_TUNNEL_SEQ_BIT, o_flags))
+		addend += 4;
+	return addend;
+}
+
+static inline void gre_flags_to_tnl_flags(unsigned long *dst, __be16 flags)
+{
+	IP_TUNNEL_DECLARE_FLAGS(res) = { };
+
+	__assign_bit(IP_TUNNEL_CSUM_BIT, res, flags & GRE_CSUM);
+	__assign_bit(IP_TUNNEL_ROUTING_BIT, res, flags & GRE_ROUTING);
+	__assign_bit(IP_TUNNEL_KEY_BIT, res, flags & GRE_KEY);
+	__assign_bit(IP_TUNNEL_SEQ_BIT, res, flags & GRE_SEQ);
+	__assign_bit(IP_TUNNEL_STRICT_BIT, res, flags & GRE_STRICT);
+	__assign_bit(IP_TUNNEL_REC_BIT, res, flags & GRE_REC);
+	__assign_bit(IP_TUNNEL_VERSION_BIT, res, flags & GRE_VERSION);
+
+	ip_tunnel_flags_copy(dst, res);
+}
+
+static inline __be16 gre_tnl_flags_to_gre_flags(const unsigned long *tflags)
+{
+	__be16 flags = 0;
+
+	if (test_bit(IP_TUNNEL_CSUM_BIT, tflags))
+		flags |= GRE_CSUM;
+	if (test_bit(IP_TUNNEL_ROUTING_BIT, tflags))
+		flags |= GRE_ROUTING;
+	if (test_bit(IP_TUNNEL_KEY_BIT, tflags))
+		flags |= GRE_KEY;
+	if (test_bit(IP_TUNNEL_SEQ_BIT, tflags))
+		flags |= GRE_SEQ;
+	if (test_bit(IP_TUNNEL_STRICT_BIT, tflags))
+		flags |= GRE_STRICT;
+	if (test_bit(IP_TUNNEL_REC_BIT, tflags))
+		flags |= GRE_REC;
+	if (test_bit(IP_TUNNEL_VERSION_BIT, tflags))
+		flags |= GRE_VERSION;
+
+	return flags;
+}
+
+static inline void gre_build_header(struct sk_buff *skb, int hdr_len,
+				    const unsigned long *flags, __be16 proto,
+				    __be32 key, __be32 seq)
+{
+	IP_TUNNEL_DECLARE_FLAGS(cond) = { };
+	struct gre_base_hdr *greh;
+
+	skb_push(skb, hdr_len);
+
+	skb_set_inner_protocol(skb, proto);
+	skb_reset_transport_header(skb);
+	greh = (struct gre_base_hdr *)skb->data;
+	greh->flags = gre_tnl_flags_to_gre_flags(flags);
+	greh->protocol = proto;
+
+	__set_bit(IP_TUNNEL_KEY_BIT, cond);
+	__set_bit(IP_TUNNEL_CSUM_BIT, cond);
+	__set_bit(IP_TUNNEL_SEQ_BIT, cond);
+
+	if (ip_tunnel_flags_intersect(flags, cond)) {
+		__be32 *ptr = (__be32 *)(((u8 *)greh) + hdr_len - 4);
+
+		if (test_bit(IP_TUNNEL_SEQ_BIT, flags)) {
+			*ptr = seq;
+			ptr--;
+		}
+		if (test_bit(IP_TUNNEL_KEY_BIT, flags)) {
+			*ptr = key;
+			ptr--;
+		}
+		if (test_bit(IP_TUNNEL_CSUM_BIT, flags) &&
+		    !(skb_shinfo(skb)->gso_type &
+		      (SKB_GSO_GRE | SKB_GSO_GRE_CSUM))) {
+			*ptr = 0;
+			if (skb->ip_summed == CHECKSUM_PARTIAL) {
+				*(__sum16 *)ptr = csum_fold(lco_csum(skb));
+			} else {
+				skb->ip_summed = CHECKSUM_PARTIAL;
+				skb->csum_start = skb_transport_header(skb) - skb->head;
+				skb->csum_offset = sizeof(*greh);
+			}
+		}
+	}
+}
+
+#endif