linux-kernel - Re: [PATCH net] ax25: Fix refcount leak issues of ax25

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Message-ID: <1e14f4f1-29dd-4fe5-8010-de7df0866e93@moroto.mountain>
Date: Sat, 4 May 2024 15:16:55 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Lars Kellogg-Stedman <lars@...bit.com>
Cc: Duoming Zhou <duoming@....edu.cn>, linux-hams@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	pabeni@...hat.com, kuba@...nel.org, edumazet@...gle.com,
	davem@...emloft.net, jreuter@...na.de
Subject: Re: [PATCH net] ax25: Fix refcount leak issues of ax25_dev

On Fri, May 03, 2024 at 07:40:32PM -0400, Lars Kellogg-Stedman wrote:
> On Fri, May 03, 2024 at 11:36:37PM +0300, Dan Carpenter wrote:
> > Could you test this diff?
> 
> With that diff applied, there is no kernel panic, but I see the same
> refcount errors that I saw before the latest series of patches from
> Duoming:

Wait, which panic is this?  The NULL dereference introduce by the
"ax25_dev" vs "res" typo?

> 
>   refcount_t: decrement hit 0; leaking memory.
>   refcount_t: underflow; use-after-free.

Hm...  Is there a missing netdev_hold() in ax25_bind() on the
"User already set interface with SO_BINDTODEVICE" path?  That would
fit with the commit 9fd75b66b8f6 ("ax25: Fix refcount leaks caused by
ax25_cb_del()") which introduced the bug.

I'm not really sure I understand how netdev_hold() works.

(My patch here is correct, but apparently that's not the bug).

regards,
dan carpenter