[PATCH] init: replace deprecated strncpy with strscpy_pad

[Justin Stitt <justinstitt@google.com>]

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 [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 init/do_mounts.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 3c5fd993bc7e..6af29da8889e 100644
--- 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);

---
base-commit: 026e680b0a08a62b1d948e5a8ca78700bfac0e6e
change-id: 20240402-strncpy-init-do_mounts-c-e1d378c88049

Best regards,
--
Justin Stitt <justinstitt@google.com>