linux-kernel - Re: [PATCH v4] net: 9p: avoid freeing uninit memory in p9pdu

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Date: Sun, 7 Jan 2024 13:14:12 +0300
From: Vitaly Chikunov <vt@...linux.org>
To: Fedor Pchelkin <pchelkin@...ras.ru>
Cc: Dominique Martinet <asmadeus@...ewreck.org>,
	Christian Schoenebeck <linux_oss@...debyte.com>,
	Eric Van Hensbergen <ericvh@...nel.org>,
	Latchesar Ionkov <lucho@...kov.net>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	v9fs@...ts.linux.dev, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Alexey Khoroshilov <khoroshilov@...ras.ru>,
	lvc-project@...uxtesting.org
Subject: Re: [PATCH v4] net: 9p: avoid freeing uninit memory in p9pdu_vreadf

Fedor,

On Sun, Jan 07, 2024 at 12:48:11PM +0300, Fedor Pchelkin wrote:
> On 24/01/07 10:56AM, Vitaly Chikunov wrote:
> > 
> > On Tue, Dec 12, 2023 at 08:21:30AM +0900, Dominique Martinet wrote:
> > > Christian Schoenebeck wrote on Thu, Dec 07, 2023 at 01:54:02PM +0100:
> > > > I just checked whether this could create a leak, but it looks clean, so LGTM:
> > > 
> > > Right, either version look good to me.
> > 
> > Also, there was unnoticed bug in v2[1] - `int i` is moved to outer block
> > and `i` counld be used uninitialized inside of `if (errcode) {`.
> 
> Could you elaborate, please? As I can see, `i` could be used
> uninitialized in `if (errcode) {` only when `*wnames` is not NULL. But
> when `*wnames` is not NULL, then `i` is initialized in the `for` loop. It
> is a bit tricky and not obvious from the first glance (and not the best
> decision after all), so with Christian's advice the patch was rewritten
> to v4 which was eventually accepted.
> 
> The bug you've noticed exists in v1 of the patch, not v2.

You are right, it only affects v1. I didn't notice that important difference
in v2. My excuses!

Thanks,

> 
> > Thanks,
> > 
> > [1] https://lore.kernel.org/all/20231205091952.24754-1-pchelkin@ispras.ru/