linux-kernel - Re: [PATCH] media: vidtv: Fix a wild pointer dereference in vidtv_channel_pmt_match

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Date:   Thu, 2 Dec 2021 14:42:19 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Zhou Qingyang <zhou1615@....edu>
Cc:     kjlu@....edu, "Daniel W. S. Almeida" <dwlsalmeida@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: vidtv: Fix a wild pointer dereference in
 vidtv_channel_pmt_match_sections()

On 30/11/2021 17:39, Zhou Qingyang wrote:
> In vidtv_channel_pmt_match_sections(), vidtv_psi_pmt_stream_init() is
> assigned to tail and &tail->descriptor is used in
> vidtv_psi_desc_assign(). There is a dereference of &tail->descriptor
> in vidtv_psi_desc_assign(), which could lead to a wild pointer
> dereference onfailure of vidtv_psi_pmt_stream_init().

onfailure -> on failure

> 
> Fix this bug by adding a check of tail.
> 
> This bug was found by a static analyzer. The analysis employs
> differential checking to identify inconsistent security operations
> (e.g., checks or kfrees) between two code paths and confirms that the
> inconsistent operations are not recovered in the current function or
> the callers, so they constitute bugs.
> 
> Note that, as a bug found by static analysis, it can be a false
> positive or hard to trigger. Multiple researchers have cross-reviewed
> the bug.
> 
> Builds with CONFIG_DVB_VIDTV=m show no new warnings,
> and our static analyzer no longer warns about this code.
> 
> Fixes: f90cf6079bf6 ("media: vidtv: add a bridge driver")
> Signed-off-by: Zhou Qingyang <zhou1615@....edu>
> ---
>  drivers/media/test-drivers/vidtv/vidtv_channel.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/media/test-drivers/vidtv/vidtv_channel.c b/drivers/media/test-drivers/vidtv/vidtv_channel.c
> index 7838e6272712..f2faa5504642 100644
> --- a/drivers/media/test-drivers/vidtv/vidtv_channel.c
> +++ b/drivers/media/test-drivers/vidtv/vidtv_channel.c
> @@ -318,6 +318,10 @@ vidtv_channel_pmt_match_sections(struct vidtv_channel *channels,
>  	struct vidtv_psi_table_pmt_stream *s = NULL;
>  	struct vidtv_channel *cur_chnl = channels;
>  	struct vidtv_psi_desc *desc = NULL;
> +	struct vidtv_mux *m = container_of(&channels,
> +					struct vidtv_mux,
> +					channels);
> +
>  	u16 e_pid; /* elementary stream pid */
>  	u16 curr_id;
>  	u32 j;
> @@ -341,6 +345,13 @@ vidtv_channel_pmt_match_sections(struct vidtv_channel *channels,
>  					tail = vidtv_psi_pmt_stream_init(tail,
>  									 s->type,
>  									 e_pid);
> +
> +					if (!tail) {
> +						vidtv_psi_pmt_stream_destroy(head);

I honestly can't tell if this is the right thing to do.

Daniel, can you take a look at this?

> +						dev_warn_ratelimited(m->dev,
> +							"No enough memory for vidtv_psi_pmt_stream_init");

No -> Not
Add newline at the end of the string.

> +						return;
> +					}
> 
>  					if (!head)
>  						head = tail;
> 

Regards,

	Hans