linux-kernel - Re: [PATCH] crypto: hisilicon/hpre - Fix a erroneous check after snprintf()

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Message-ID: <71bf9b84-462f-405e-91aa-fb21fc6ffbd5@moroto.mountain>
Date:   Thu, 7 Sep 2023 14:15:33 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     Marion & Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Longfang Liu <liulongfang@...wei.com>,
        "David S. Miller" <davem@...emloft.net>,
        Zaibo Xu <xuzaibo@...wei.com>, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-crypto@...r.kernel.org
Subject: Re: [PATCH] crypto: hisilicon/hpre - Fix a erroneous check after
 snprintf()

On Tue, Sep 05, 2023 at 07:27:47AM +0200, Marion & Christophe JAILLET wrote:
> > 
> > The other snprintf in the same file also looks suspect.
> 
> It looks correct to me.
> 
> And HPRE_DBGFS_VAL_MAX_LEN being 20, it doesn't really matter. The string
> can't be truncated with just a "%u\n".
> 

drivers/crypto/hisilicon/hpre/hpre_main.c
   884          ret = snprintf(tbuf, HPRE_DBGFS_VAL_MAX_LEN, "%u\n", val);
   885          return simple_read_from_buffer(buf, count, pos, tbuf, ret);

You can't pass the return value from snprintf() to simple_read_from_buffer().
Otherwise the snprintf() checking turned a sprintf() write overflow into
a read overflow, which is less bad but not ideal.  It needs to be
scnprintf().

regards,
dan carpenter