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, 68 insertions, 0 deletions

diff --git a/fs/nls/nls_utf8.c b/fs/nls/nls_utf8.c
new file mode 100644
index 000000000..a0fa0610e
--- /dev/null
+++ b/fs/nls/nls_utf8.c
@@ -0,0 +1,68 @@
+/*
+ * Module for handling utf8 just like any other charset.
+ * By Urban Widmark 2000
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/nls.h>
+#include <linux/errno.h>
+
+static unsigned char identity[256];
+
+static int uni2char(wchar_t uni, unsigned char *out, int boundlen)
+{
+	int n;
+
+	if (boundlen <= 0)
+		return -ENAMETOOLONG;
+
+	n = utf32_to_utf8(uni, out, boundlen);
+	if (n < 0) {
+		*out = '?';
+		return -EINVAL;
+	}
+	return n;
+}
+
+static int char2uni(const unsigned char *rawstring, int boundlen, wchar_t *uni)
+{
+	int n;
+	unicode_t u;
+
+	n = utf8_to_utf32(rawstring, boundlen, &u);
+	if (n < 0 || u > MAX_WCHAR_T) {
+		*uni = 0x003f;	/* ? */
+		return -EINVAL;
+	}
+	*uni = (wchar_t) u;
+	return n;
+}
+
+static struct nls_table table = {
+	.charset	= "utf8",
+	.uni2char	= uni2char,
+	.char2uni	= char2uni,
+	.charset2lower	= identity,	/* no conversion */
+	.charset2upper	= identity,
+};
+
+static int __init init_nls_utf8(void)
+{
+	int i;
+	for (i=0; i<256; i++)
+		identity[i] = i;
+
+        return register_nls(&table);
+}
+
+static void __exit exit_nls_utf8(void)
+{
+        unregister_nls(&table);
+}
+
+module_init(init_nls_utf8)
+module_exit(exit_nls_utf8)
+MODULE_DESCRIPTION("NLS UTF-8");
+MODULE_LICENSE("Dual BSD/GPL");