selftests/bpf: Reject graph kptr use after RCU unlockgrafted

Add a sleepable verifier test that loads a graph-node local kptr in an
explicit RCU read-side critical section, then passes its node to
bpf_rbtree_remove() after the section ends.

Before the verifier fix, the stale NON_OWN_REF flag makes the node look like
a live borrowed reference and the program is accepted. After the fix, the
pointer is demoted without NON_OWN_REF and the graph kfunc argument is
rejected.

Also exercise a graph kptr loaded while a spin lock provides implicit RCU
protection. The pointer must be invalidated when the lock is released, which
guards the required ordering between non-owning-reference invalidation and
RCU demotion.

Update the existing fault-protected load test state description. The
post-unlock pointer no longer carries NON_OWN_REF, but remains readable
because the load is rewritten to use BPF_PROBE_MEM.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 63 insertions, 0 deletions

diff --git a/include/net/inet_dscp.h b/include/net/inet_dscp.h
new file mode 100644
index 000000000..1aa9f04ed
--- /dev/null
+++ b/include/net/inet_dscp.h
@@ -0,0 +1,63 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * inet_dscp.h: helpers for handling differentiated services codepoints (DSCP)
+ *
+ * DSCP is defined in RFC 2474:
+ *
+ *        0   1   2   3   4   5   6   7
+ *      +---+---+---+---+---+---+---+---+
+ *      |         DSCP          |  CU   |
+ *      +---+---+---+---+---+---+---+---+
+ *
+ *        DSCP: differentiated services codepoint
+ *        CU:   currently unused
+ *
+ * The whole DSCP + CU bits form the DS field.
+ * The DS field is also commonly called TOS or Traffic Class (for IPv6).
+ *
+ * Note: the CU bits are now used for Explicit Congestion Notification
+ *       (RFC 3168).
+ */
+
+#ifndef _INET_DSCP_H
+#define _INET_DSCP_H
+
+#include <linux/types.h>
+
+/* Special type for storing DSCP values.
+ *
+ * A dscp_t variable stores a DS field with the CU (ECN) bits cleared.
+ * Using dscp_t allows to strictly separate DSCP and ECN bits, thus avoiding
+ * bugs where ECN bits are erroneously taken into account during FIB lookups
+ * or policy routing.
+ *
+ * Note: to get the real DSCP value contained in a dscp_t variable one would
+ * have to do a bit shift after calling inet_dscp_to_dsfield(). We could have
+ * a helper for that, but there's currently no users.
+ */
+typedef u8 __bitwise dscp_t;
+
+#define INET_DSCP_MASK 0xfc
+
+/* A few places in the IPv4 code need to ignore the three high order bits of
+ * DSCP because of backward compatibility (as these bits used to represent the
+ * IPv4 Precedence in RFC 791's TOS field and were ignored).
+ */
+#define INET_DSCP_LEGACY_TOS_MASK ((__force dscp_t)0x1c)
+
+static inline dscp_t inet_dsfield_to_dscp(__u8 dsfield)
+{
+	return (__force dscp_t)(dsfield & INET_DSCP_MASK);
+}
+
+static inline __u8 inet_dscp_to_dsfield(dscp_t dscp)
+{
+	return (__force __u8)dscp;
+}
+
+static inline bool inet_validate_dscp(__u8 val)
+{
+	return !(val & ~INET_DSCP_MASK);
+}
+
+#endif /* _INET_DSCP_H */