Re: [PATCH] media: bttv: Fix a NULL pointer dereference in setup_window_lock()

[Greg KH]

On Tue, Jan 25, 2022 at 01:05:13AM +0800, Zhou Qingyang wrote:
> In setup_window_lock(), the return value of videobuf_sg_alloc() is
> assigned to variable new and there is a dereference of it after
> that. the return value of videobuf_sg_alloc() could be NULL on
> failure of allocation, which could lead to a NULL pointer dereference.
> 
> Fix this bug by adding a NULL check of new.
> 
> This bug was found by a static analyzer.
> 
> Builds with 'make allyesconfig' show no new warnings,
> and our static analyzer no longer warns about this code.
> 
> Fixes: e5bd0260e7d3 ("V4L/DVB (5077): Bttv cropping support")
> Signed-off-by: Zhou Qingyang <zhou1615@xxxxxxx>
> ---
> 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.
> 
>  drivers/media/pci/bt8xx/bttv-driver.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/media/pci/bt8xx/bttv-driver.c b/drivers/media/pci/bt8xx/bttv-driver.c
> index 8cc9bec43688..6338f98d845d 100644
> --- a/drivers/media/pci/bt8xx/bttv-driver.c
> +++ b/drivers/media/pci/bt8xx/bttv-driver.c
> @@ -2182,6 +2182,8 @@ static int setup_window_lock(struct bttv_fh *fh, struct bttv *btv,
>  		struct bttv_buffer *new;
>  
>  		new = videobuf_sg_alloc(sizeof(*new));
> +		if (!new)
> +			return -ENOMEM;
>  		new->crop = btv->crop[!!fh->do_crop].rect;
>  		bttv_overlay_risc(btv, &fh->ov, fh->ovfmt, new);
>  		retval = bttv_switch_overlay(btv,fh,new);
> -- 
> 2.25.1
> 

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