linux-kernel - Re: [PATCH v2 1/2] crypto: Fix -Wstringop-truncation warnings

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Date:   Mon, 25 Jun 2018 22:40:21 +0900
From:   Stafford Horne <shorne@...il.com>
To:     Christophe LEROY <christophe.leroy@....fr>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>, arnd@...db.de,
        Eric Biggers <ebiggers3@...il.com>,
        linux-crypto@...r.kernel.org, Max Filippov <jcmvbkbc@...il.com>,
        Nick Desaulniers <nick.desaulniers@...il.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v2 1/2] crypto: Fix -Wstringop-truncation warnings

On Mon, Jun 25, 2018 at 02:59:58PM +0200, Christophe LEROY wrote:
> 
> 
> Le 25/06/2018 à 14:45, Stafford Horne a écrit :
> > As of GCC 9.0.0 the build is reporting warnings like:
> > 
> >      crypto/ablkcipher.c: In function ‘crypto_ablkcipher_report’:
> >      crypto/ablkcipher.c:374:2: warning: ‘strncpy’ specified bound 64 equals destination size [-Wstringop-truncation]
> >        strncpy(rblkcipher.geniv, alg->cra_ablkcipher.geniv ?: "<default>",
> >        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >         sizeof(rblkcipher.geniv));
> >         ~~~~~~~~~~~~~~~~~~~~~~~~~
> > 
> > This means the strnycpy might create a non null terminated string.  Fix this by
> > explicitly performing '\0' termination.
> > 
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Cc: Arnd Bergmann <arnd@...db.de>
> > Cc: Max Filippov <jcmvbkbc@...il.com>
> > Cc: Eric Biggers <ebiggers3@...il.com>
> > Cc: Nick Desaulniers <nick.desaulniers@...il.com>
> > Signed-off-by: Stafford Horne <shorne@...il.com>
> > ---
> >   crypto/ablkcipher.c | 2 ++
> >   crypto/blkcipher.c  | 1 +
> >   2 files changed, 3 insertions(+)
> > 
> > diff --git a/crypto/ablkcipher.c b/crypto/ablkcipher.c
> > index d880a4897159..1edb5000d783 100644
> > --- a/crypto/ablkcipher.c
> > +++ b/crypto/ablkcipher.c
> > @@ -373,6 +373,7 @@ static int crypto_ablkcipher_report(struct sk_buff *skb, struct crypto_alg *alg)
> >   	strncpy(rblkcipher.type, "ablkcipher", sizeof(rblkcipher.type));
> >   	strncpy(rblkcipher.geniv, alg->cra_ablkcipher.geniv ?: "<default>",
> >   		sizeof(rblkcipher.geniv));
> 
> Is it worth copying something we are going to discard at the following line
> ? Shouldn't you limit the copy to      sizeof(rblkcipher.geniv) - 1   ?

Hi,

I thought about that, I just did it like this as I thought it might be easier to
read and I noticed a few other areas in the kernel that did this way.  After a
closer look I can see we have both patterns, perhaps we need a mcro/helper.

I don't mind either way, I can fix, if the crypto maintainers want to adjust the
patch that would work too.

-Stafford

> > +	rblkcipher.geniv[sizeof(rblkcipher.geniv) - 1] = '\0';
> >   	rblkcipher.blocksize = alg->cra_blocksize;
> >   	rblkcipher.min_keysize = alg->cra_ablkcipher.min_keysize;
> > @@ -447,6 +448,7 @@ static int crypto_givcipher_report(struct sk_buff *skb, struct crypto_alg *alg)
> >   	strncpy(rblkcipher.type, "givcipher", sizeof(rblkcipher.type));
> >   	strncpy(rblkcipher.geniv, alg->cra_ablkcipher.geniv ?: "<built-in>",
> >   		sizeof(rblkcipher.geniv));
> 
> Same comment here.
> 
> Christophe
> 
> > +	rblkcipher.geniv[sizeof(rblkcipher.geniv) - 1] = '\0';
> >   	rblkcipher.blocksize = alg->cra_blocksize;
> >   	rblkcipher.min_keysize = alg->cra_ablkcipher.min_keysize;
> > diff --git a/crypto/blkcipher.c b/crypto/blkcipher.c
> > index 01c0d4aa2563..dd4dcab3766a 100644
> > --- a/crypto/blkcipher.c
> > +++ b/crypto/blkcipher.c
> > @@ -512,6 +512,7 @@ static int crypto_blkcipher_report(struct sk_buff *skb, struct crypto_alg *alg)
> >   	strncpy(rblkcipher.type, "blkcipher", sizeof(rblkcipher.type));
> >   	strncpy(rblkcipher.geniv, alg->cra_blkcipher.geniv ?: "<default>",
> >   		sizeof(rblkcipher.geniv));
> > +	rblkcipher.geniv[sizeof(rblkcipher.geniv) - 1] = '\0';
> >   	rblkcipher.blocksize = alg->cra_blocksize;
> >   	rblkcipher.min_keysize = alg->cra_blkcipher.min_keysize;
> >