bpf: mark a NULL kfunc argument precisegrafted

check_kfunc_arg() allows bpf_register_is_null() for nullable arguments
w/o marking the underlying scalar register precise. Hence a checkpoint
created on such a path would prune against arbitrary scalar value.

Fixes: 3bda08b63670 ("bpf: Allow NULL buffers in bpf_dynptr_slice(_rw)")
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260904-register-is-null-precise-fixes-v1-5-0f5a360ff15d@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 47 insertions, 0 deletions

diff --git a/security/selinux/include/hash.h b/security/selinux/include/hash.h
new file mode 100644
index 000000000..18956dbef
--- /dev/null
+++ b/security/selinux/include/hash.h
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef _SELINUX_HASH_H_
+#define _SELINUX_HASH_H_
+
+/*
+ * Based on MurmurHash3, written by Austin Appleby and placed in the
+ * public domain.
+ */
+static inline u32 av_hash(u32 key1, u32 key2, u32 key3, u32 mask)
+{
+	static const u32 c1 = 0xcc9e2d51;
+	static const u32 c2 = 0x1b873593;
+	static const u32 r1 = 15;
+	static const u32 r2 = 13;
+	static const u32 m = 5;
+	static const u32 n = 0xe6546b64;
+
+	u32 hash = 0;
+
+#define mix(input)                                         \
+	do {                                               \
+		u32 v = input;                             \
+		v *= c1;                                   \
+		v = (v << r1) | (v >> (32 - r1));          \
+		v *= c2;                                   \
+		hash ^= v;                                 \
+		hash = (hash << r2) | (hash >> (32 - r2)); \
+		hash = hash * m + n;                       \
+	} while (0)
+
+	mix(key1);
+	mix(key2);
+	mix(key3);
+
+#undef mix
+
+	hash ^= hash >> 16;
+	hash *= 0x85ebca6b;
+	hash ^= hash >> 13;
+	hash *= 0xc2b2ae35;
+	hash ^= hash >> 16;
+
+	return hash & mask;
+}
+
+#endif /* _SELINUX_HASH_H_ */