[PATCH v2] keys: Replace deprecated strncpy in ecryptfs_fill_auth_tok

[Jarkko Sakkinen]

On Fri, Oct 10, 2025 at 06:13:41PM +0200, Thorsten Blum wrote:
> strncpy() is deprecated for NUL-terminated destination buffers; use
> strscpy_pad() instead to retain the zero-padding behavior of strncpy().
> 
> strscpy_pad() automatically determines the size of the fixed-length
> destination buffer via sizeof() when the optional size argument is
> omitted, making an explicit size unnecessary.
> 
> In encrypted_init(), the source string 'key_desc' is validated by
> valid_ecryptfs_desc() before calling ecryptfs_fill_auth_tok(), and is
> therefore NUL-terminated and satisfies the __must_be_cstr() requirement
> of strscpy_pad().
> 
> No functional changes.

It's a functional change (for better!) because it transforms to safer
semantics ;-) And yeah as years pass by commit messages like these
have more value than code changes themselves (as far backtracking
and bisecting is concerned).

So if you don't mind, I'll delete the very last one sentence paragraph,
and with that

Reviewed-by: Jarkko Sakkinen <jarkko at kernel.org>

Thank you.

> 
> Link: https://github.com/KSPP/linux/issues/90
> Signed-off-by: Thorsten Blum <thorsten.blum at linux.dev>
> ---
> Changes in v2:
> - Improve commit message as suggested by Jarkko and Kees
> - Link to v1: https://lore.kernel.org/lkml/20251009180316.394708-3-thorsten.blum@linux.dev/
> ---
>  security/keys/encrypted-keys/ecryptfs_format.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/security/keys/encrypted-keys/ecryptfs_format.c b/security/keys/encrypted-keys/ecryptfs_format.c
> index 8fdd76105ce3..2fc6f3a66135 100644
> --- a/security/keys/encrypted-keys/ecryptfs_format.c
> +++ b/security/keys/encrypted-keys/ecryptfs_format.c
> @@ -54,8 +54,7 @@ int ecryptfs_fill_auth_tok(struct ecryptfs_auth_tok *auth_tok,
>  	auth_tok->version = (((uint16_t)(major << 8) & 0xFF00)
>  			     | ((uint16_t)minor & 0x00FF));
>  	auth_tok->token_type = ECRYPTFS_PASSWORD;
> -	strncpy((char *)auth_tok->token.password.signature, key_desc,
> -		ECRYPTFS_PASSWORD_SIG_SIZE);
> +	strscpy_pad(auth_tok->token.password.signature, key_desc);
>  	auth_tok->token.password.session_key_encryption_key_bytes =
>  		ECRYPTFS_MAX_KEY_BYTES;
>  	/*
> -- 
> 2.51.0
> 

BR, Jarkko