linux-hardening - Re: [PATCH 7/7] netfilter: xtables: refactor deprecated strncpy

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Date:   Wed, 9 Aug 2023 01:20:34 +0200 (CEST)
From:   Jan Engelhardt <jengelh@...i.de>
To:     Justin Stitt <justinstitt@...gle.com>
cc:     Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        linux-hardening@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] netfilter: xtables: refactor deprecated strncpy


On Wednesday 2023-08-09 00:48, Justin Stitt wrote:

>Prefer `strscpy` as it's a more robust interface.
>
>There may have existed a bug here due to both `tbl->repl.name` and
>`info->name` having a size of 32 as defined below:
>|  #define XT_TABLE_MAXNAMELEN 32
>
>This may lead to buffer overreads in some situations -- `strscpy` solves
>this by guaranteeing NUL-termination of the dest buffer.

It generally will not lead to overreads.
xt not only deals with strings on its own turf, it even takes
them from userspace-provided buffers, which means extra scrutiny is
absolutely required. Done in places like

x_tables.c:     if (strnlen(name, XT_EXTENSION_MAXNAMELEN) == XT_EXTENSION_MAXNAMELEN)


(Which is not to say the strncpy->strscpy mop-up is bad.)