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, 114 insertions, 0 deletions

diff --git a/include/net/dropreason-qdisc.h b/include/net/dropreason-qdisc.h
new file mode 100644
index 000000000..fb151cd31
--- /dev/null
+++ b/include/net/dropreason-qdisc.h
@@ -0,0 +1,114 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _LINUX_DROPREASON_QDISC_H
+#define _LINUX_DROPREASON_QDISC_H
+#include <net/dropreason.h>
+
+#define DEFINE_QDISC_DROP_REASON(FN, FNe)	\
+	FN(UNSPEC)			\
+	FN(GENERIC)			\
+	FN(OVERLIMIT)			\
+	FN(CONGESTED)			\
+	FN(MAXFLOWS)			\
+	FN(FLOOD_PROTECTION)		\
+	FN(BAND_LIMIT)		\
+	FN(HORIZON_LIMIT)		\
+	FN(FLOW_LIMIT)			\
+	FN(L4S_STEP_NON_ECN)		\
+	FNe(MAX)
+
+#undef FN
+#undef FNe
+#define FN(reason)	QDISC_DROP_##reason,
+#define FNe(reason)	QDISC_DROP_##reason
+
+/**
+ * enum qdisc_drop_reason - reason why a qdisc dropped a packet
+ *
+ * Qdisc-specific drop reasons for packet drops that occur within the
+ * traffic control (TC) queueing discipline layer. These reasons provide
+ * detailed diagnostics about why packets were dropped by various qdisc
+ * algorithms, enabling fine-grained monitoring and troubleshooting of
+ * queue behavior.
+ */
+enum qdisc_drop_reason {
+	/**
+	 * @QDISC_DROP_UNSPEC: unspecified/invalid qdisc drop reason.
+	 * Value 0 serves as analogous to SKB_NOT_DROPPED_YET for enum skb_drop_reason.
+	 * Used for catching zero-initialized drop_reason fields.
+	 */
+	QDISC_DROP_UNSPEC = 0,
+	/**
+	 * @__QDISC_DROP_REASON: subsystem base value for qdisc drop reasons
+	 */
+	__QDISC_DROP_REASON = SKB_DROP_REASON_SUBSYS_QDISC <<
+				SKB_DROP_REASON_SUBSYS_SHIFT,
+	/**
+	 * @QDISC_DROP_GENERIC: generic/default qdisc drop, used when no
+	 * more specific reason applies
+	 */
+	QDISC_DROP_GENERIC,
+	/**
+	 * @QDISC_DROP_OVERLIMIT: packet dropped because the qdisc queue
+	 * length exceeded its configured limit (sch->limit). This typically
+	 * indicates the queue is full and cannot accept more packets.
+	 */
+	QDISC_DROP_OVERLIMIT,
+	/**
+	 * @QDISC_DROP_CONGESTED: packet dropped due to active congestion
+	 * control algorithms (e.g., CoDel, PIE, RED) detecting network
+	 * congestion. The qdisc proactively dropped the packet to signal
+	 * congestion to the sender and prevent bufferbloat.
+	 */
+	QDISC_DROP_CONGESTED,
+	/**
+	 * @QDISC_DROP_MAXFLOWS: packet dropped because the qdisc's flow
+	 * tracking table is full and no free slots are available to allocate
+	 * for a new flow. This indicates flow table exhaustion in flow-based
+	 * qdiscs that maintain per-flow state (e.g., SFQ).
+	 */
+	QDISC_DROP_MAXFLOWS,
+	/**
+	 * @QDISC_DROP_FLOOD_PROTECTION: packet dropped by flood protection
+	 * mechanism detecting unresponsive flows (potential DoS/flood).
+	 * Used by qdiscs implementing probabilistic drop algorithms like
+	 * BLUE (e.g., CAKE's Cobalt AQM).
+	 */
+	QDISC_DROP_FLOOD_PROTECTION,
+	/**
+	 * @QDISC_DROP_BAND_LIMIT: packet dropped because the priority band's
+	 * limit was reached. Used by qdiscs with priority bands that have
+	 * per-band packet limits (e.g., FQ).
+	 */
+	QDISC_DROP_BAND_LIMIT,
+	/**
+	 * @QDISC_DROP_HORIZON_LIMIT: packet dropped because its timestamp
+	 * is too far in the future (beyond the configured horizon).
+	 * Used by qdiscs with time-based scheduling (e.g., FQ).
+	 */
+	QDISC_DROP_HORIZON_LIMIT,
+	/**
+	 * @QDISC_DROP_FLOW_LIMIT: packet dropped because an individual flow
+	 * exceeded its per-flow packet/depth limit. Used by FQ and SFQ qdiscs
+	 * to enforce per-flow fairness and prevent a single flow from
+	 * monopolizing queue resources.
+	 */
+	QDISC_DROP_FLOW_LIMIT,
+	/**
+	 * @QDISC_DROP_L4S_STEP_NON_ECN: DualPI2 qdisc dropped a non-ECN-capable
+	 * packet because the L4S queue delay exceeded the step threshold.
+	 * Since the packet cannot be ECN-marked, it must be dropped to signal
+	 * congestion. See RFC 9332 for the DualQ Coupled AQM step mechanism.
+	 */
+	QDISC_DROP_L4S_STEP_NON_ECN,
+	/**
+	 * @QDISC_DROP_MAX: the maximum of qdisc drop reasons, which
+	 * shouldn't be used as a real 'reason' - only for tracing code gen
+	 */
+	QDISC_DROP_MAX,
+};
+
+#undef FN
+#undef FNe
+
+#endif