init: replace deprecated strncpy with strscpy_pad

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

data_page wants to be NUL-terminated and NUL-padded, use strscpy_pad to
provide both of these. data_page no longer awkwardly relies on
init_mount to perform its NUL-termination, although that sanity check is
left unchanged.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
Link: https://github.com/KSPP/linux/issues/90
Cc:  <linux-hardening@vger.kernel.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20240402-strncpy-init-do_mounts-c-v1-1-e16d7bc20974@google.com
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 3c5fd993bc7e3e955f322e506bdad8aea8e0edbb..6af29da8889ebf675b98cef92ad80923adec79f9 100644 (file)
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -159,8 +159,7 @@ static int __init do_mount_root(const char *name, const char *fs,
                if (!p)
                        return -ENOMEM;
                data_page = page_address(p);
-               /* zero-pad. init_mount() will make sure it's terminated */
-               strncpy(data_page, data, PAGE_SIZE);
+               strscpy_pad(data_page, data, PAGE_SIZE);
        }
 
        ret = init_mount(name, "/root", fs, flags, data_page);