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

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Message-ID: <8e527ade-fe49-4697-8e36-589775c63354@moroto.mountain>
Date: Thu, 11 Jan 2024 10:15:40 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Kees Cook <keescook@...omium.org>
Cc: "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
	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 Wed, Jan 10, 2024 at 04:03:28PM -0800, Kees Cook wrote:
> 
> Oops, yes, thanks for fixing my confusion. Right, this is a direct write
> across members into the flex array, not a composite destination. Yay
> all the corner cases. :P

Is there a document somewhere which explains what will trigger a runtime
warning?  For example, if you write across members but it's not into a
flex array does that cause an issue?  Or if you read across members?

For example, this line reads from bulletin->vlan and
bulletin->vlan_padding.  This causes a compiler warning in Clang and
GCC depending on the options but does it also trigger a runtime warning?
https://elixir.bootlin.com/linux/latest/source/drivers/net/ethernet/broadcom/bnx2x/bnx2x_sriov.c#L2655

(I wrote a patch for this a few months back but didn't send it because
of the merge window.  I forgot about it until now that we're in a merge
window again...  :P)

regards,
dan carpenter