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, 98 insertions, 0 deletions

diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
new file mode 100644
index 000000000..2945aa7fe
--- /dev/null
+++ b/include/trace/events/skb.h
@@ -0,0 +1,98 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM skb
+
+#if !defined(_TRACE_SKB_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_SKB_H
+
+#include <linux/skbuff.h>
+#include <linux/netdevice.h>
+#include <linux/tracepoint.h>
+
+#undef FN
+#define FN(reason)	TRACE_DEFINE_ENUM(SKB_DROP_REASON_##reason);
+DEFINE_DROP_REASON(FN, FN)
+
+#undef FN
+#undef FNe
+#define FN(reason)	{ SKB_DROP_REASON_##reason, #reason },
+#define FNe(reason)	{ SKB_DROP_REASON_##reason, #reason }
+
+/*
+ * Tracepoint for free an sk_buff:
+ */
+TRACE_EVENT(kfree_skb,
+
+	TP_PROTO(struct sk_buff *skb, void *location,
+		 enum skb_drop_reason reason, const struct sock *rx_sk),
+
+	TP_ARGS(skb, location, reason, rx_sk),
+
+	TP_STRUCT__entry(
+		__field(void *,		skbaddr)
+		__field(void *,		location)
+		__field(const void *,	rx_sk)
+		__field(unsigned short,	protocol)
+		__field(enum skb_drop_reason,	reason)
+	),
+
+	TP_fast_assign(
+		__entry->skbaddr = skb;
+		__entry->location = location;
+		__entry->rx_sk = rx_sk;
+		__entry->protocol = ntohs(skb->protocol);
+		__entry->reason = reason;
+	),
+
+	TP_printk("skbaddr=%p rx_sk=%p protocol=%u location=%pS reason: %s",
+		  __entry->skbaddr, __entry->rx_sk, __entry->protocol,
+		  __entry->location,
+		  __print_symbolic(__entry->reason,
+				   DEFINE_DROP_REASON(FN, FNe)))
+);
+
+#undef FN
+#undef FNe
+
+TRACE_EVENT(consume_skb,
+
+	TP_PROTO(struct sk_buff *skb, void *location),
+
+	TP_ARGS(skb, location),
+
+	TP_STRUCT__entry(
+		__field(	void *,	skbaddr)
+		__field(	void *,	location)
+	),
+
+	TP_fast_assign(
+		__entry->skbaddr = skb;
+		__entry->location = location;
+	),
+
+	TP_printk("skbaddr=%p location=%pS", __entry->skbaddr, __entry->location)
+);
+
+TRACE_EVENT(skb_copy_datagram_iovec,
+
+	TP_PROTO(const struct sk_buff *skb, int len),
+
+	TP_ARGS(skb, len),
+
+	TP_STRUCT__entry(
+		__field(	const void *,		skbaddr		)
+		__field(	int,			len		)
+	),
+
+	TP_fast_assign(
+		__entry->skbaddr = skb;
+		__entry->len = len;
+	),
+
+	TP_printk("skbaddr=%p len=%d", __entry->skbaddr, __entry->len)
+);
+
+#endif /* _TRACE_SKB_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>