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

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

[Zhou Qingyang]

In bttv_overlay(), 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: 7c018804c090 ("V4L/DVB (7197): bttv: Fix overlay divide error")
Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
---
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 6338f98d845d..5aa46593ddc6 100644
--- a/drivers/media/pci/bt8xx/bttv-driver.c
+++ b/drivers/media/pci/bt8xx/bttv-driver.c
@@ -2552,6 +2552,8 @@ static int bttv_overlay(struct file *file, void *f, unsigned int on)
 	if (on) {
 		fh->ov.tvnorm = btv->tvnorm;
 		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);
 	} else {
-- 
2.25.1

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

[Greg KH]

On Tue, Jan 25, 2022 at 01:26:24AM +0800, Zhou Qingyang wrote:
> In bttv_overlay(), 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: 7c018804c090 ("V4L/DVB (7197): bttv: Fix overlay divide error")
> Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
> ---
> 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 6338f98d845d..5aa46593ddc6 100644
> --- a/drivers/media/pci/bt8xx/bttv-driver.c
> +++ b/drivers/media/pci/bt8xx/bttv-driver.c
> @@ -2552,6 +2552,8 @@ static int bttv_overlay(struct file *file, void *f, unsigned int on)
>  	if (on) {
>  		fh->ov.tvnorm = btv->tvnorm;
>  		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);
>  	} else {
> -- 
> 2.25.1
> 

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