linux-kernel - Re: [PATCH v2 2/2] VMCI: Fix memcpy() run-time warning in dg_dispatch_as

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Date: Tue, 9 Jan 2024 06:31:41 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Kees Cook <keescook@...omium.org>,
 Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>,
 linux-hardening@...r.kernel.org, error27@...il.com, gustavoars@...nel.org,
 Bryan Tan <bryantan@...are.com>, Vishnu Dasa <vdasa@...are.com>,
 VMware PV-Drivers Reviewers <pv-drivers@...are.com>,
 Arnd Bergmann <arnd@...db.de>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 linux-kernel@...r.kernel.org, vegard.nossum@...cle.com,
 darren.kenny@...cle.com, syzkaller <syzkaller@...glegroups.com>
Subject: Re: [PATCH v2 2/2] VMCI: Fix memcpy() run-time warning in
 dg_dispatch_as_host()

On 1/9/24 03:07, Dan Carpenter wrote:
> On Mon, Jan 08, 2024 at 08:05:38PM -0600, Gustavo A. R. Silva wrote:
>>>> Gustavo quoted:
>>>> "Under FORTIFY_SOURCE we should not copy data across multiple members
>>>> in a structure."
>>>>
>>>> Reported-by: syzkaller <syzkaller@...glegroups.com>
>>>> Suggested-by: Vegard Nossum <vegard.nossum@...cle.com>
>>>> Suggested-by: Gustavo A. R. Silva <gustavoars@...nel.org>
>>>> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
>>>
>>> Thanks for getting this fixed!
>>>
>>> Yeah, it's a "false positive" in the sense that the code was expecting
>>
>> It's a false positive _bug_, and a legitimate _warning_ coming from fortified
>> memcpy().
> 
> It really feels like you're trying to sell the cost of this as a good
> thing...  We've already merged fortify so why are you still fighting

No, I'm just describing (here[1] and below), clear and concise, what fortify
is doing in this particular case, in response to your first intervention
in this thread[3].

"The warning is triggered because of a write beyond the boundaries of
`dg_info->msg`."[2]

You're arguing that fortify caused a problem. I'm describing the reason
why the feature triggered the warning. That's it, I guess.

Thanks
--
Gustavo

[1] https://lore.kernel.org/linux-hardening/9c742547-0021-464b-b7a8-7af46b0a4afa@embeddedor.com/
[2] https://lore.kernel.org/linux-hardening/7826922a-d642-424e-bede-bfc45be9254d@embeddedor.com/
[3] https://lore.kernel.org/linux-hardening/fc132bde-d42d-4aac-ba91-7a939a18091a@moroto.mountain/