Revert "HID: uhid: use strlcpy() instead of strncpy()"

David Herrmann · Jiri Kosina · commit 4d26d1d1e806 · 2018-11-19T14:32:27.000+01:00
This reverts commit 336fd4f. Please note that `strlcpy()` does *NOT* do what you think it does. strlcpy() *ALWAYS* reads the full input string, regardless of the 'length' parameter. That is, if the input is not zero-terminated, strlcpy() will *READ* beyond input boundaries. It does this, because it always returns the size it *would* copy if the target was big enough, not the truncated size it actually copied. The original code was perfectly fine. The hid device is zero-initialized and the strncpy() functions copied up to n-1 characters. The result is always zero-terminated this way. This is the third time someone tried to replace strncpy with strlcpy in this function, and gets it wrong. I now added a comment that should at least make people reconsider. Signed-off-by: David Herrmann <dh.herrmann@gmail.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
@@ -497,12 +497,13 @@ static int uhid_dev_create2(struct uhid_device *uhid,
 		goto err_free;
 	}
 
-	len = min(sizeof(hid->name), sizeof(ev->u.create2.name));
-	strlcpy(hid->name, ev->u.create2.name, len);
-	len = min(sizeof(hid->phys), sizeof(ev->u.create2.phys));
-	strlcpy(hid->phys, ev->u.create2.phys, len);
-	len = min(sizeof(hid->uniq), sizeof(ev->u.create2.uniq));
-	strlcpy(hid->uniq, ev->u.create2.uniq, len);
+	/* @hid is zero-initialized, strncpy() is correct, strlcpy() not */
+	len = min(sizeof(hid->name), sizeof(ev->u.create2.name)) - 1;
+	strncpy(hid->name, ev->u.create2.name, len);
+	len = min(sizeof(hid->phys), sizeof(ev->u.create2.phys)) - 1;
+	strncpy(hid->phys, ev->u.create2.phys, len);
+	len = min(sizeof(hid->uniq), sizeof(ev->u.create2.uniq)) - 1;
+	strncpy(hid->uniq, ev->u.create2.uniq, len);
 
 	hid->ll_driver = &uhid_hid_driver;
 	hid->bus = ev->u.create2.bus;
