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

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Message-ID: <CAMo8BfLZi5NBr-rjGd8y88t8o=e9q-Mra05GJbH5OtUvXZhZgw@mail.gmail.com>
Date:   Fri, 22 Jun 2018 19:22:20 -0700
From:   Max Filippov <jcmvbkbc@...il.com>
To:     Stafford Horne <shorne@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>, linux-crypto@...r.kernel.org,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [RFC PATCH 1/2] crypto: Fix -Wstringop-truncation warnings

On Fri, Jun 22, 2018 at 7:07 PM, Stafford Horne <shorne@...il.com> wrote:
> 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
> limiting the size of the string copy to include the null terminator.

That could work if the destination buffer was zero-initialized,
but it's allocated on stack and is not initialized.
Replacing strncpy with strlcpy without changing its arguments
should do the right thing.

-- 
Thanks.
-- Max