[PATCH] Squashfs: replace deprecated strncpy with strscpy

[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.

The previous code took special care of NUL-terminating the destination
buffer via a manual assignment. As such, there is no bug in the current
implementation. However, in an effort to rid the kernel of strscpy()
[2], Let's instead use strscpy() which guarantees this behavior [3]. To
ensure we can copy the same number of bytes as before, add 1 to the
length argument provided to strscpy().

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://github.com/KSPP/linux/issues/90 [2]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html  [3]
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Note: build-tested only.

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

diff --git a/fs/squashfs/namei.c b/fs/squashfs/namei.c
index 11e4539b9eae..6c4704ba8f42 100644
--- a/fs/squashfs/namei.c
+++ b/fs/squashfs/namei.c
@@ -80,8 +80,7 @@ static int get_dir_index_using_name(struct super_block *sb,
 	}
 
 	str = &index->name[SQUASHFS_NAME_LEN + 1];
-	strncpy(str, name, len);
-	str[len] = '\0';
+	strscpy(str, name, len + 1);
 
 	for (i = 0; i < i_count; i++) {
 		err = squashfs_read_metadata(sb, index, &index_start,

---
base-commit: 928a87efa42302a23bb9554be081a28058495f22
change-id: 20240328-strncpy-fs-squashfs-namei-c-9d01b8975e53

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