linux-kernel - Re: [PATCH v3] keys: Replace deprecated strncpy in ecryptfs_fill_auth

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Message-ID: <b9246396-c9d9-4452-a16c-f2c8166a32ee@molgen.mpg.de>
Date: Mon, 13 Oct 2025 18:11:38 +0200
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Thorsten Blum <thorsten.blum@...ux.dev>
Cc: Mimi Zohar <zohar@...ux.ibm.com>, David Howells <dhowells@...hat.com>,
 Jarkko Sakkinen <jarkko@...nel.org>, Paul Moore <paul@...l-moore.com>,
 James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>,
 linux-hardening@...r.kernel.org, Kees Cook <kees@...nel.org>,
 linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
 linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] keys: Replace deprecated strncpy in
 ecryptfs_fill_auth_tok

Dear Thorsten,


Thank you for the patch.

Am 13.10.25 um 17:26 schrieb Thorsten Blum:
> strncpy() is deprecated for NUL-terminated destination buffers; use
> strscpy_pad() instead to retain the NUL-padding behavior of strncpy().
> 
> The destination buffer is initialized using kzalloc() with a 'signature'
> size of ECRYPTFS_PASSWORD_SIG_SIZE + 1. strncpy() then copies up to
> ECRYPTFS_PASSWORD_SIG_SIZE bytes from 'key_desc', NUL-padding any
> remaining bytes if needed, but expects the last byte to be zero.
> 
> strscpy_pad() also copies the source string to 'signature', and NUL-pads
> the destination buffer if needed, but ensures it's always NUL-terminated
> without relying on it being zero-initialized.
> 
> 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().
> 
> Link: https://github.com/KSPP/linux/issues/90
> Reviewed-by: Kees Cook <kees@...nel.org>
> Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
> Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
> ---
> Changes in v3:
> - Improve commit message
> - Link to v2: https://lore.kernel.org/lkml/20251010161340.458707-2-thorsten.blum@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;
>   	/*

Reviewed-by: Paul Menzel <pmenzel@...gen.mpg.de>


Kind regards,

Paul