HID: simplify snto32()

jira LE-4321
cve CVE-2025-38556
Rebuild_History Non-Buildable kernel-4.18.0-553.76.1.el8_10
commit-author Dmitry Torokhov <dmitry.torokhov@gmail.com>
commit ae9b956

snto32() does exactly what sign_extend32() does, but handles
potentially malformed data coming from the device. Keep the checks,
but then call sign_extend32() to perform the actual conversion.

	Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Link: https://patch.msgid.link/20241003144656.3786064-1-dmitry.torokhov@gmail.com
	Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
(cherry picked from commit ae9b956)
	Signed-off-by: Jonathan Maple <jmaple@ciq.com>

Author: PlaidCat

drivers/hid/hid-core.c

@@ -1300,9 +1300,7 @@ int hid_open_report(struct hid_device *device)
 EXPORT_SYMBOL_GPL(hid_open_report);
 
 /*
- * Convert a signed n-bit integer to signed 32-bit integer. Common
- * cases are done through the compiler, the screwed things has to be
- * done by hand.
+ * Convert a signed n-bit integer to signed 32-bit integer.
  */
 
 static s32 snto32(__u32 value, unsigned n)
@@ -1313,12 +1311,7 @@ static s32 snto32(__u32 value, unsigned n)
 	if (n > 32)
 		n = 32;
 
-	switch (n) {
-	case 8:  return ((__s8)value);
-	case 16: return ((__s16)value);
-	case 32: return ((__s32)value);
-	}
-	return value & (1 << (n - 1)) ? value | (~0U << n) : value;
+	return sign_extend32(value, n - 1);
 }
 
 s32 hid_snto32(__u32 value, unsigned n)