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, 91 insertions, 0 deletions

diff --git a/drivers/usb/gadget/usbstring.c b/drivers/usb/gadget/usbstring.c
new file mode 100644
index 000000000..37a2f1b61
--- /dev/null
+++ b/drivers/usb/gadget/usbstring.c
@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: LGPL-2.1+
+/*
+ * Copyright (C) 2003 David Brownell
+ */
+
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/list.h>
+#include <linux/string.h>
+#include <linux/device.h>
+#include <linux/nls.h>
+
+#include <linux/usb/ch9.h>
+#include <linux/usb/gadget.h>
+
+
+/**
+ * usb_gadget_get_string - fill out a string descriptor 
+ * @table: of c strings encoded using UTF-8
+ * @id: string id, from low byte of wValue in get string descriptor
+ * @buf: at least 256 bytes, must be 16-bit aligned
+ *
+ * Finds the UTF-8 string matching the ID, and converts it into a
+ * string descriptor in utf16-le.
+ * Returns length of descriptor (always even) or negative errno
+ *
+ * If your driver needs stings in multiple languages, you'll probably
+ * "switch (wIndex) { ... }"  in your ep0 string descriptor logic,
+ * using this routine after choosing which set of UTF-8 strings to use.
+ * Note that US-ASCII is a strict subset of UTF-8; any string bytes with
+ * the eighth bit set will be multibyte UTF-8 characters, not ISO-8859/1
+ * characters (which are also widely used in C strings).
+ */
+int
+usb_gadget_get_string (const struct usb_gadget_strings *table, int id, u8 *buf)
+{
+	struct usb_string	*s;
+	int			len;
+
+	/* descriptor 0 has the language id */
+	if (id == 0) {
+		buf [0] = 4;
+		buf [1] = USB_DT_STRING;
+		buf [2] = (u8) table->language;
+		buf [3] = (u8) (table->language >> 8);
+		return 4;
+	}
+	for (s = table->strings; s && s->s; s++)
+		if (s->id == id)
+			break;
+
+	/* unrecognized: stall. */
+	if (!s || !s->s)
+		return -EINVAL;
+
+	/* string descriptors have length, tag, then UTF16-LE text */
+	len = min_t(size_t, USB_MAX_STRING_LEN, strlen(s->s));
+	len = utf8s_to_utf16s(s->s, len, UTF16_LITTLE_ENDIAN,
+			(wchar_t *) &buf[2], USB_MAX_STRING_LEN);
+	if (len < 0)
+		return -EINVAL;
+	buf [0] = (len + 1) * 2;
+	buf [1] = USB_DT_STRING;
+	return buf [0];
+}
+EXPORT_SYMBOL_GPL(usb_gadget_get_string);
+
+/**
+ * usb_validate_langid - validate usb language identifiers
+ * @langid: usb language identifier
+ *
+ * Returns true for valid language identifier, otherwise false.
+ */
+bool usb_validate_langid(u16 langid)
+{
+	u16 primary_lang = langid & 0x3ff;	/* bit [9:0] */
+	u16 sub_lang = langid >> 10;		/* bit [15:10] */
+
+	switch (primary_lang) {
+	case 0:
+	case 0x62 ... 0xfe:
+	case 0x100 ... 0x3ff:
+		return false;
+	}
+	if (!sub_lang)
+		return false;
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(usb_validate_langid);