linux-kernel - Re: [PATCH] media: vidtv: fix to initialize local pointers upon transfer of memory ownership

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Message-Id: <7FD2157E-6F0B-40E0-9984-7485845DAC51@gmail.com>
Date: Fri, 22 Aug 2025 10:40:16 -0300
From: Daniel Almeida <dwlsalmeida@...il.com>
To: Jeongjun Park <aha310510@...il.com>
Cc: mchehab@...nel.org,
 linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 syzbot+1d9c0edea5907af239e0@...kaller.appspotmail.com
Subject: Re: [PATCH] media: vidtv: fix to initialize local pointers upon
 transfer of memory ownership

Hi Jeongjun,

> On 22 Aug 2025, at 03:58, Jeongjun Park <aha310510@...il.com> wrote:
> 
> vidtv_channel_si_init() transfers ownership of each object to the correct
> table through functions such as vidtv_psi_*_assign().
> 
> However, since it does not set the local pointer to NULL afterwards, if it
> fails for various reasons and jumps to a place such as free_*it, memory
> that was freed in vidtv_psi_*_table_destroy() will be accessed and freed
> again, resulting in use-after-free and double-free vuln.

I get what you’re trying to say, but what you actually wrote is hard to
parse, can you improve the wording here?

> 
> Therefore, local pointers that have completed ownership transfer must be
> initialized to NULL to prevent re-access to already freed memory.
> 
> Reported-by: syzbot+1d9c0edea5907af239e0@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=1d9c0edea5907af239e0
> Fixes: 3be8037960bc ("media: vidtv: add error checks")
> Signed-off-by: Jeongjun Park <aha310510@...il.com>
> ---
> drivers/media/test-drivers/vidtv/vidtv_channel.c | 3 +++
> 1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/media/test-drivers/vidtv/vidtv_channel.c b/drivers/media/test-drivers/vidtv/vidtv_channel.c
> index f3023e91b3eb..3541155c6fc6 100644
> --- a/drivers/media/test-drivers/vidtv/vidtv_channel.c
> +++ b/drivers/media/test-drivers/vidtv/vidtv_channel.c
> @@ -461,12 +461,15 @@ int vidtv_channel_si_init(struct vidtv_mux *m)
> 
> /* assemble all programs and assign to PAT */
> vidtv_psi_pat_program_assign(m->si.pat, programs);
> + programs = NULL;
> 
> /* assemble all services and assign to SDT */
> vidtv_psi_sdt_service_assign(m->si.sdt, services);
> + services = NULL;
> 
> /* assemble all events and assign to EIT */
> vidtv_psi_eit_event_assign(m->si.eit, events);
> + events = NULL;
> 
> m->si.pmt_secs = vidtv_psi_pmt_create_sec_for_each_pat_entry(m->si.pat,
>     m->pcr_pid);
> --

The patch itself is ok, thanks a lot, however:

> media: vidtv: fix to initialize local pointers upon transfer of memory ownership

Can you please use imperative voice here? i.e.:

"media: vidtv: initialize local pointers upon transfer of memory ownership”

— Daniel