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Date:   Mon, 16 Oct 2023 10:01:20 -0700
From:   Kees Cook <kees@kernel.org>
To:     Dan Carpenter <dan.carpenter@linaro.org>,
        Simon Horman <horms@kernel.org>
CC:     Justin Stitt <justinstitt@google.com>,
        Thomas Sailer <t.sailer@alumni.ethz.ch>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, linux-hams@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-hardening@vger.kernel.org
Subject: Re: [PATCH] hamradio: replace deprecated strncpy with strscpy
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References: <20231012-strncpy-drivers-net-hamradio-baycom_epp-c-v1-1-8f4097538ee4@google.com> <20231015150619.GC1386676@kernel.org> <ede96908-76ff-473c-a5e1-39e2ce130df9@kadam.mountain>
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On October 15, 2023 10:47:53 PM PDT, Dan Carpenter <dan=2Ecarpenter@linaro=
=2Eorg> wrote:
>On Sun, Oct 15, 2023 at 05:06:19PM +0200, Simon Horman wrote:
>> On Thu, Oct 12, 2023 at 09:33:32PM +0000, Justin Stitt wrote:
>> > strncpy() is deprecated for use on NUL-terminated destination strings
>> > [1] and as such we should prefer more robust and less ambiguous strin=
g
>> > interfaces=2E
>> >=20
>> > We expect both hi=2Edata=2Emodename and hi=2Edata=2Edrivername to be
>> > NUL-terminated but not necessarily NUL-padded which is evident by its
>> > usage with sprintf:
>> > |       sprintf(hi=2Edata=2Emodename, "%sclk,%smodem,fclk=3D%d,bps=3D=
%d%s",
>> > |               bc->cfg=2Eintclk ? "int" : "ext",
>> > |               bc->cfg=2Eextmodem ? "ext" : "int", bc->cfg=2Efclk, b=
c->cfg=2Ebps,
>> > |               bc->cfg=2Eloopback ? ",loopback" : "");
>> >=20
>> > Note that this data is copied out to userspace with:
>> > |       if (copy_to_user(data, &hi, sizeof(hi)))
>> > =2E=2E=2E however, the data was also copied FROM the user here:
>> > |       if (copy_from_user(&hi, data, sizeof(hi)))
>>=20
>> Thanks Justin,
>>=20
>> I see that too=2E
>>=20
>> Perhaps I am off the mark here, and perhaps it's out of scope for this
>> patch, but I do think it would be nicer if the kernel only sent
>> intended data to user-space, even if any unintended payload came
>> from user-space=2E
>>=20
>
>It's kind of normal to pass user space data back to itself=2E  We
>generally only worry about info leaks=2E

True but since this used to zero the rest of the buffet, let's just keep t=
hat behavior and use strscpy_pad()=2E

-Kees

--=20
Kees Cook