linux-kernel - Re: tcp: Checking a kmemdup() call in tcp_time

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Message-ID: <124b41aa-7ba5-f00c-ab73-cb8e6a2ae75f@gmail.com>
Date:   Sun, 13 Oct 2019 12:45:53 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Markus Elfring <Markus.Elfring@....de>, netdev@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Hideaki Yoshifuji <yoshfuji@...ux-ipv6.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org, Aditya Pakki <pakki001@....edu>,
        Kangjie Lu <kjlu@....edu>, Navid Emamdoost <emamd001@....edu>,
        Stephen McCamant <smccaman@....edu>
Subject: Re: tcp: Checking a kmemdup() call in tcp_time_wait()



On 10/12/19 7:51 AM, Markus Elfring wrote:
> Hello,
> 
> I tried another script for the semantic patch language out.
> This source code analysis approach points out that the implementation
> of the function “tcp_time_wait” contains also a call of the function “kmemdup”.
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/net/ipv4/tcp_minisocks.c?id=1c0cc5f1ae5ee5a6913704c0d75a6e99604ee30a#n306
> https://elixir.bootlin.com/linux/v5.4-rc2/source/net/ipv4/tcp_minisocks.c#L306
> 
> * Do you find the usage of the macro call “BUG_ON” still appropriate at this place?
>   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/checkpatch.pl?id=1c0cc5f1ae5ee5a6913704c0d75a6e99604ee30a#n4080
> 
> * Is there a need to adjust the error handling here?

Presumably the BUG would trigger if a really disturbing bug happened.

There is no chance a timewait socket could be created with a MD5 key, 
if the established socket that is the 'parent' of the timewait
has not a MD5 context itself.

The parent socket only could have MD5 context if tcp_md5sig_pool_populated
could have been set to true.

Once tcp_md5sig_pool_populated is true it can never go back to false.

So the bug here would be that a socket  had a successful MD5 context,
and following tcp_alloc_md5sig_pool() would return false.

We can discuss of all BUG() in general, some people simply disable
all of them (cf CONFIG_BUG), but this particular one does not seem
specially bad to me, compared to others.