linux-kernel - Re: [PATCH v2] [PATCH] KEYS: trusted: fix -Wvarags warning

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Message-ID: <20181023000051.GA17367@flashbox>
Date:   Mon, 22 Oct 2018 17:00:51 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     ndesaulniers@...gle.com
Cc:     dhowells@...hat.com, jejb@...ux.vnet.ibm.com,
        David.Laight@...lab.com, denkenz@...il.com,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH v2] [PATCH] KEYS: trusted: fix -Wvarags warning

On Mon, Oct 22, 2018 at 04:43:57PM -0700, ndesaulniers@...gle.com wrote:
> Fixes the warning reported by Clang:
> security/keys/trusted.c:146:17: warning: passing an object that
> undergoes default
>       argument promotion to 'va_start' has undefined behavior [-Wvarargs]
>         va_start(argp, h3);
>                        ^
> security/keys/trusted.c:126:37: note: parameter of type 'unsigned
> char' is declared here
> unsigned char *h2, unsigned char h3, ...)
>                                ^
> Specifically, it seems that both the C90 (4.8.1.1) and C11 (7.16.1.4)
> standards explicitly call this out as undefined behavior:
> 
> The parameter parmN is the identifier of the rightmost parameter in
> the variable parameter list in the function definition (the one just
> before the ...). If the parameter parmN is declared with ... or with a
> type that is not compatible with the type that results after
> application of the default argument promotions, the behavior is
> undefined.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/41
> Link: https://www.eskimo.com/~scs/cclass/int/sx11c.html
> Suggested-by: David Laight <David.Laight@...lab.com>
> Suggested-by: Denis Kenzior <denkenz@...il.com>
> Suggested-by: James Bottomley <jejb@...ux.vnet.ibm.com>
> Suggested-by: Nathan Chancellor <natechancellor@...il.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Tested-by: Nathan Chancellor <natechancellor@...il.com>

> ---
> v1 -> v2:
> * Don't reorder args, just use default function promotion type
> of unsigned int.
> * Add !! boolean cast as per Denis in
> https://lkml.org/lkml/2018/10/12/838.
> * Tested with gcc-8 and clang-8.
> 
>  include/keys/trusted.h  | 2 +-
>  security/keys/trusted.c | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/include/keys/trusted.h b/include/keys/trusted.h
> index adbcb6817826..0071298b9b28 100644
> --- a/include/keys/trusted.h
> +++ b/include/keys/trusted.h
> @@ -38,7 +38,7 @@ enum {
>  
>  int TSS_authhmac(unsigned char *digest, const unsigned char *key,
>  			unsigned int keylen, unsigned char *h1,
> -			unsigned char *h2, unsigned char h3, ...);
> +			unsigned char *h2, unsigned int h3, ...);
>  int TSS_checkhmac1(unsigned char *buffer,
>  			  const uint32_t command,
>  			  const unsigned char *ononce,
> diff --git a/security/keys/trusted.c b/security/keys/trusted.c
> index ff6789365a12..335ce6d1cf6b 100644
> --- a/security/keys/trusted.c
> +++ b/security/keys/trusted.c
> @@ -123,7 +123,7 @@ static int TSS_rawhmac(unsigned char *digest, const unsigned char *key,
>   */
>  int TSS_authhmac(unsigned char *digest, const unsigned char *key,
>  			unsigned int keylen, unsigned char *h1,
> -			unsigned char *h2, unsigned char h3, ...)
> +			unsigned char *h2, unsigned int h3, ...)
>  {
>  	unsigned char paramdigest[SHA1_DIGEST_SIZE];
>  	struct sdesc *sdesc;
> @@ -139,7 +139,7 @@ int TSS_authhmac(unsigned char *digest, const unsigned char *key,
>  		return PTR_ERR(sdesc);
>  	}
>  
> -	c = h3;
> +	c = !!h3;
>  	ret = crypto_shash_init(&sdesc->shash);
>  	if (ret < 0)
>  		goto out;
> -- 
> 2.19.1.568.g152ad8e336-goog
> 

Thank you for the fix!
Nathan