linux-kernel - Re: [PATCH v3] media: vidtv: initialize local pointers upon transfer of memory ownership

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Message-Id: <96EC5D66-18D8-42E6-BD3F-F07F220EA5EE@collabora.com>
Date: Fri, 5 Sep 2025 09:53:46 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Jeongjun Park <aha310510@...il.com>
Cc: mchehab@...nel.org,
 linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 stable@...r.kernel.org,
 syzbot+1d9c0edea5907af239e0@...kaller.appspotmail.com
Subject: Re: [PATCH v3] media: vidtv: initialize local pointers upon transfer
 of memory ownership



> On 5 Sep 2025, at 02:18, Jeongjun Park <aha310510@...il.com> wrote:
> 
> vidtv_channel_si_init() creates a temporary list (program, service, event)
> and ownership of the memory itself is transferred to the PAT/SDT/EIT
> tables through vidtv_psi_pat_program_assign(),
> vidtv_psi_sdt_service_assign(), vidtv_psi_eit_event_assign().
> 
> The problem here is that the local pointer where the memory ownership
> transfer was completed is not initialized to NULL. This causes the
> vidtv_psi_pmt_create_sec_for_each_pat_entry() function to fail, and
> in the flow that jumps to free_eit, the memory that was freed by
> vidtv_psi_*_table_destroy() can be accessed again by
> vidtv_psi_*_event_destroy() due to the uninitialized local pointer, so it
> is freed once again.
> 
> Therefore, to prevent use-after-free and double-free vulnerability,
> local pointers must be initialized to NULL when transferring memory
> ownership.
> 
> Cc: <stable@...r.kernel.org>
> 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>
> ---
> v3: Improved patch description wording
> - Link to v2: https://lore.kernel.org/all/20250904054000.3848107-1-aha310510@gmail.com/
> v2: Improved patch description wording and CC stable mailing list
> - Link to v1: https://lore.kernel.org/all/20250822065849.1145572-1-aha310510@gmail.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);
> —
> 

Reviewed-by: Daniel Almeida <daniel.almeida@...labora.com>