linux-kernel - Re: drivers/md/dm-cache-metadata.c:1705:9: warning: 'strncpy' specified bound 16 equals destination size

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Date:   Fri, 29 Sep 2023 10:49:45 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        justinstitt@...gle.com
Cc:     kernel test robot <lkp@...el.com>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...nel.org>,
        oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>
Subject: Re: drivers/md/dm-cache-metadata.c:1705:9: warning: 'strncpy'
 specified bound 16 equals destination size

On Thu, Sep 28, 2023 at 11:36:46AM +0200, Miguel Ojeda wrote:
> On Thu, Sep 28, 2023 at 12:24 AM kernel test robot <lkp@...el.com> wrote:
> >
> >    In function 'write_hints',
> >        inlined from 'dm_cache_write_hints' at drivers/md/dm-cache-metadata.c:1729:6:
> > >> drivers/md/dm-cache-metadata.c:1705:9: warning: 'strncpy' specified bound 16 equals destination size [-Wstringop-truncation]
> >     1705 |         strncpy(cmd->policy_name, policy_name, sizeof(cmd->policy_name));
> >          |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> This looks fine given the check above it. In any case, since it
> appears the code wants to terminate the string, this should use
> `strscpy*()`, right?

I agree. I can't tell if _pad is needed though. I think struct
dm_cache_metadata is only used internally? And I see at least the
initial allocation is zeroed:

        cmd = kzalloc(sizeof(*cmd), GFP_KERNEL);

Regardless, for background,

struct has:
        char policy_name[CACHE_POLICY_NAME_SIZE];

code does:
        const char *policy_name = dm_cache_policy_get_name(policy);

        if (!policy_name[0] ||
            (strlen(policy_name) > sizeof(cmd->policy_name) - 1))
                return -EINVAL;

        strncpy(cmd->policy_name, policy_name, sizeof(cmd->policy_name));


Justin, can you add this to your queue (if it's not already there)?

-Kees

-- 
Kees Cook