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

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

Posted by Jeongjun Park 5 months, 2 weeks ago

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.

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@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=1d9c0edea5907af239e0
Fixes: 3be8037960bc ("media: vidtv: add error checks")
Signed-off-by: Jeongjun Park <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);
--

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

Posted by Daniel Almeida 5 months, 2 weeks ago

Hi Jeongjun,

> On 22 Aug 2025, at 03:58, Jeongjun Park <aha310510@gmail.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@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=1d9c0edea5907af239e0
> Fixes: 3be8037960bc ("media: vidtv: add error checks")
> Signed-off-by: Jeongjun Park <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);
> --

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

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

Posted by Jeongjun Park 5 months, 2 weeks ago

Hello Daniel,


Daniel Almeida <dwlsalmeida@gmail.com> wrote:
>
> Hi Jeongjun,
>
> > On 22 Aug 2025, at 03:58, Jeongjun Park <aha310510@gmail.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?

Oops, I think I made the explanation difficult to understand and confusing.
I'll try to rewrite it so it's as easy to understand as possible.

>
> >
> > 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@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=1d9c0edea5907af239e0
> > Fixes: 3be8037960bc ("media: vidtv: add error checks")
> > Signed-off-by: Jeongjun Park <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);
> > --
>
> 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”

If I do that, the patch subject will change. Should I just change the
subject and send it to you, or should I also send it with the v2 tag
included?

>
> — Daniel

Regards,
Jeongjun Park

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

Posted by Daniel Almeida 5 months, 2 weeks ago

[…]

>>> --
>> 
>> 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”
> 
> If I do that, the patch subject will change. Should I just change the
> subject and send it to you, or should I also send it with the v2 tag
> included?

Just change the subject and send it to the list with the v2 tag.

Also, I just realize that you should rewrite this further: “Set local
pointers to NULL upon transfer of memory ownership” or something around
these lines.

— Daniel

> 
>> 
>> — Daniel
> 
> Regards,
> Jeongjun Park