selftests/bpf: Test rhtab kptr cancellation semanticsgrafted

Resizable hash-map updates and deletions must not perform full special-field
destruction in their caller context. In particular, a referenced kptr must
remain attached to the allocation until the memory allocator destructor can
release it safely.

Add separate coverage for both affected paths. The update test stores a task
kptr, replaces the ordinary value bytes with BPF_EXIST, and verifies that the
kptr survived. The delete test removes an element and exchanges its kptr
through the still-valid map-value pointer before the allocation is reclaimed.

Both cases observe a NULL kptr when rhtab uses bpf_obj_free_fields(). They
recover and release the reference after rhtab switches to cancellation
semantics.

Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
[ kkd: Split update and delete coverage and rewrote the commit log ]
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904104203.345917-5-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 56 insertions, 0 deletions

diff --git a/net/batman-adv/bitarray.h b/net/batman-adv/bitarray.h
new file mode 100644
index 000000000..2b9f5dbb3
--- /dev/null
+++ b/net/batman-adv/bitarray.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) B.A.T.M.A.N. contributors:
+ *
+ * Simon Wunderlich, Marek Lindner
+ */
+
+#ifndef _NET_BATMAN_ADV_BITARRAY_H_
+#define _NET_BATMAN_ADV_BITARRAY_H_
+
+#include "main.h"
+
+#include <linux/bitops.h>
+#include <linux/compiler.h>
+#include <linux/stddef.h>
+#include <linux/types.h>
+
+/**
+ * batadv_test_bit() - check if bit is set in the current window
+ *
+ * @seq_bits: pointer to the sequence number bitmap of received packets
+ * @last_seqno: latest sequence number in seq_bits
+ * @curr_seqno: sequence number to test for
+ *
+ * Return: true if the corresponding bit in the given seq_bits indicates true
+ * and curr_seqno is within range of last_seqno. Otherwise returns false.
+ */
+static inline bool batadv_test_bit(const unsigned long *seq_bits,
+				   u32 last_seqno, u32 curr_seqno)
+{
+	s32 diff;
+
+	diff = last_seqno - curr_seqno;
+	if (diff < 0 || diff >= BATADV_TQ_LOCAL_WINDOW_SIZE)
+		return false;
+	return test_bit(diff, seq_bits) != 0;
+}
+
+/**
+ * batadv_set_bit() - Turn corresponding bit on, so we can remember that we got
+ *  the packet
+ * @seq_bits: bitmap of the packet receive window
+ * @n: relative sequence number of newly received packet
+ */
+static inline void batadv_set_bit(unsigned long *seq_bits, s32 n)
+{
+	/* if too old, just drop it */
+	if (n < 0 || n >= BATADV_TQ_LOCAL_WINDOW_SIZE)
+		return;
+
+	set_bit(n, seq_bits); /* turn the position on */
+}
+
+bool batadv_bit_get_packet(void *priv, unsigned long *seq_bits,
+			   s32 seq_num_diff, int set_mark);
+
+#endif /* _NET_BATMAN_ADV_BITARRAY_H_ */